CERTIFICATE OF ORIGINALITY

I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree or diploma of a university or other institute of higher learning, except where due acknowledgement is made in the text.

(Signed) A CORDLESS GUN Research and Design of a New Product

CHATREE TANG-AMATAKUL

Graduate School of The Built Environment University of New South Wales 1989 UNIVERSITY Or N.S.W. 2 9 JUN 1990 LIBRARY CONTENTS

ABSTRACT ...... i ACKNOWLEDGMENTS ...... iii CHAPTER 1 INTRODUCTION AND BACKGROUND TO RESEARCH.

1.1 Introduction ...... 1

1.2 Overview of nailing ...... 2 1.3 The development of cordless ...... 5

CHAPTER 2 OVERALL METHODOLOGY AND STRATEGY. 2.1 Introduction ...... 9 2.2 Objectives ...... 9

2.3 Methodology ...... 10 2.4 Design process ...... 25

CHAPTER 3 NAILING IN WOODWORK.

3.1 Introduction ...... 26 3.2 Principle and practice ...... 26 3.3 Percussive force ...... 28 3.4 Types of nail and their uses ...... 30 3.5 Nail driving tools ...... 34

3.6 Conclusion ...... 43

CHAPTER 4 SUMMARY OF ENGINEERING FACTORS. 4.1 Ergonomic principles ...... 44 4.2 Design mechanism ...... 47

CHAPTER 5 EXPERIMENTAL AND MOCK UP TESTING. 5.1 Introduction ...... 53 5.2 Experimental testing of nailing principles ...... 53 5.3 Experimental testing of spring force

for driving nails ...... 60

5.4 Testing of mock up ...... 63

5.5 Conclusion ...... 70

5.6 Implications of the experimental and mock up testing ...... 71 CHAPTER 6 DESIGN.

6.1 Design criteria ...... 73 6.2 Design concepts ...... 77 6.3 Design development ...... 106

6.4 The final design ...... Ill 6.5 Conclusion Evaluation of the design .... 136 BIBLIOGRAPHY...... 138 ABSTRACT

The project investigates nailing and the tools available for manual and power nail driving. The problems of these tools are identified and a proposal developed for the design of a nail gun, which is safe, suitable for domestic as well as industrial applications, portable and suitable for the retail market. The methodology used practical experiments and a survey of the literature. This included experimental testing of the factors involved in nailing, surveying existing designs, a brief questionnaire/discussion with users, a literature review and consultation with engineering experts. The experimental and mock up test determined that a spring actuated mechanism of 4 Nm of stored energy could be used for driving nails, and that such a mechanism can be modified to be power driven. Further experiment established that it could be powered by a MAKITA rechargeable battery pack 9.6V. It was shown that this mechanism can drive a nail of 2.5 mm dia .* 50 mm into soft within 2 seconds. The final design is a portable power for driving common wire nails, which is both cordless and rechargeable. The design process shows the development of the design from initial concepts to a final design which meets the requirements of ergonomics, function, aesthetics and

i production. The design is presented as a set of orthographic drawings, photographs of a working mock up to show the mechanical/electrical principles and photographs of a full size block model.

ii ACKNOWLEDGMENTS

The author wishes to extend thanks to John Redmond,

Head of Department of Industrial Design, UNSW., for advice and encouragement during the conduct of the project. Appreciation is also expressed to David Bray,

Laboratory technician in the Faculty of Architecture ;

Bill Lawson, School of Architecture; Ron Dennis and

Kelvin Hunt, School of Mechanical and Industrial

Engineering; and Wolfgang Kohler the engineering consultant for the project, whose assistance has been invaluable.

I wish to thank my sponsor, Australian International

Development Assistance Bureau for the scholarship that enable me to undertake the course; my English tutor,

Mrs. Gabi Duigu for grammatically checking the various drafts.

Lastly I would like to thank my wife, Chaveewan for special encouragement throughout.

iii CHAPTER 1

INTRODUCTION AND BACKGROUND TO RESEARCH

1.1 Introduction. Although the design of most common hand tools has evolved over many years, many of them are difficult to use and in some cases unsafe. Problems mentioned by ergonomists include carpal tunnel syndrome, vasoconstriction, tenosynovitis and epicondy1its . (Tichauer and Crage, 1977.).

Fig.1.1 Showing the effect of a tool improperly designed for user health. (a) . Improper design: The need for ulnar or radial deviation of the wrist ( the posture with bent wrist ) when using the tool can

cause Tenosynovitis.

(b) . Re-design: The re-designed handle allows more normal alignment of the wrist.

1 In recent years ergonomics has become of crucial importance in industrial design. Many new as well as re­ designed products have shown the benefit of an ergonomic

approach.

Among the tools that could benefit from a re-assessment

is the which has certain disadvantages in its

present form. For example fingers can easily be hit and it is inconvenient to use when driving a nail upwards or at an awkward angle.

In recent years many hand tools such as , , planners, and drivers etc. have been designed to be power driven, using a variety of power sources, such as pneumatics, powder explosives, internal combustion and electricity. A recent type of power source which seems to be increasingly applied is the rechargeable battery, or nickel-cadmium cell. Tools using this type of power source are called " cordless tools" or " rechargeable power tools". The operator is free to use them virtually anywhere and in complete safety with no inconvenient cable reels to deal with.

1.2 Overview of nailing. At present, nailing can be undertaken by two methods. One is by use of the conventional hammer which comes

with a variety of heads. Another method is by use of a

nail gun which is available with different kinds of power source such as pneumatics, electricity and

explosives. Manual hammering is often a cause of injury

2 to the user. Quite often the user's fingers are hit by

the hammer as the nail must be held when starting to

hammer. This is especially so when using small nails.

Fig.1.2 Fingers may be struck whilst holding the

nail when starting to hammer.

The second difficulty is that sometimes nailing is not

successful as the nail bends during hammering,

especially when nailing into hard wood. The design

itself can also cause confusion for beginners. The

center of gravity of the hammer is located at the head,

and the grip position is far from the center of gravity.

This makes the tool unbalanced to hold. Unskilled users

often try to hold the hammer close to the head as it

makes the hammer more balanced in their hands; however

this is not an effective way to hammer. Another

difficulty in using a hammer is that it is difficult to

nail upwards such as when working on a ceiling because

the posture of the user becomes awkward, involving bending of the neck and ulnar deviation of the wrist.

3 Fig.1.3 Nailing upward causes difficulty to the user because of awkward posture. However, from the point of view of a skilled worker, these difficulties are not a major concern. The only disadvantage they find is that the process is slow. While nail guns resolve some of these problems, some problems remain: Existing nail guns using electric, pneumatic and explosive power, are not available as general tools for the house-holder or handy-person. They are generally designed for factory or manufacturing processes as their powerful action can cause serious accidents, when used by unskilled operators. Injuries caused by ricocheting nails are a particular hazard. Another disadvantage of existing units is that they normally require a special type of nail for each brand of gun. Very few models can use the general flat head or bullet head nail which is available in most hardware shops.

4 1.3 The development of cordless tools. The first cordless power tools were developed in the

early 1970s. The objective was to eliminate mains cables

running around sites and workshops. Typically the users would carry a bulky and heavy battery pack attached to the belt with a short lead connecting it to the tool. By

the early 1980s, nickel-cadmium technology meant that not only could battery packs be integral to the tool but charging time was down to one hour or less ( Building Trades Journal, Jan. 1986 ).

In recent years cordless tools have become widely used and a variety of types of tools are available on the market, such as cordless drills, jigsaws, drivers, torches and mowers etc. A more recent innovation in cordless tools has been the rechargeable power pack which can be easily removed for charging and the tool re-loaded with a fully charged one. As a spare battery pack is available, the tool can be kept in almost continuous operation. Some examples of existing cordless tools are shown below :

5 The Bosch 11213 Rotary hammer.

Fig.1.4 The Bosch 11213 industrial

rotary hammer .

This is powered by a 24 v battery. It can easily drill holes in concrete up to 14 mm diameter and with the hammer feature off it can drill holes up to 20 mm diameter in steel.( Building Trade Journal. June, 1986).

Cordless electric mower

The TORO machine is powered by a fully enclosed 12 v four pole permanent magnet motor with a top operating speed of 3350 rpm. The mower is started by gripping the handle; when the operator releases the handle the mower stops automatically in less than a second. It will operate 45 minutes on one charge and the weight is 55 lbs. ( Product Engineering. Oct., 1974. ).

6 Fig.1.5 The TORO cordless electric mower.

The Black and Decker interchangeable energy pack tools.

(a). (b). ^ Fig.1.6 The Black and Decker

interchangeable energy pack tools.

(a) . A grass shear. (b) . A 1/4 inch drill.

The universal rechargeable high-energy pack, housed in the tool's handle, can be used for seven different Mod-4 tools : a grass shear, an up-right grass shear, a shrub

7 trimmer, a 1/4 inch drill, a sealed beam lantern, a 1 quart sprayer and a 1 gallon sprayer. It consists of four Nickel-Cadmium cells. One charge will provide enough power to shear the grass around 1 acre, or allow the drill to make 130 1/4 inch holes in 2 inch thick wood. ( Product Engineering. Oct., 1974. ).

8 CHAPTER 2

OVERALL METHODOLOGY AND STRATEGY

2.1 Introduction. In order to conduct research into the design of a cordless nail gun, a number of factors were identified for consideration.

2.2 Objectives. Before setting up a design strategy, the objectives of the research need to be defined so that a methodology can be developed. The objectives to be achieved in the first stage can be described as follows :

To understand nailing techniques. To understand problems with nailing.

To obtain information about existing tools for driving nails.

To obtain information about existing types of nails.

To establish the principles of design for power hand tools.

To understand the mechanism of existing hand held power tools.

To obtain information about cordless tools.

9 2.3 Methodology. As the objectives to be achieved were general and tentative and the boundary was indefinite, a divergent methodology was applied in order to establish the widest possible view of the product area. The methods chosen were as follows: 1. Questionnaire of users. 2. Observational : studies of nailing techniques, existing nail guns and their uses. 3. Literature search.

4. Experimental testing : nailing principles and spring impacted force; testing of mock ups of various designs.

5. Consultation with engineering experts.

2.3.1 Questionnaire of users. Aims: To discuss general requirements with a range of potential users to help identify design parameters.

The restrictions of the project and the perceived benefits of questionnaire surveys about products not already on the market were such that a large scale statistically based survey was not considered to be appropriate. Instead, it was considered that informal discussions with a number of potential users would general trends and information. However because the author is a non-native English

10 speaker it was decided to use a questionnaire to aid communication rather than use face to face discussion.

Method. Two groups of people were selected as subjects for questioning. The first group contained 20 persons, who were carpenters and handy persons. Eight persons were staff of UNSW from different departments, such as maintenance, Faculty of Architecture and School of

Chemistry. The others were handy persons who were resident in the suburb around UNSW. The second group contained 15 persons who were tool retailers and hardware salesmen in shops around UNSW. As an aid to communication, questionnaire forms were handed out to all subjects. Most of them replied while the author was waiting and they were completed and returned in around 5-10 minutes as the forms contained only 10 short questions.

Results of the replies to the questionnaire.

The responses of the questionnaire were analyzed and the following conclusions, which must be regarded as anecdotal in nature rather than quantitative, were reached :

Males seem to be the major users of power tools for driving nails and they could be carpenters, handy persons and manufacturers. Most of them consider that a reasonable price for such a tool would be between $150

11 and $250. The commonly used nails are bullet head and flat head nails of between 25 mm to 65 mm in length. The

materials nailed are basically hard wood and soft wood

and there is no general requirement to drive nails into masonry. It is regarded as preferable to have the charger unit of cordless tools separate from the tool.

2.3.2 Observations: nailing techniques; use of nail gun; existing power tools on the market.

Observations included a study of wood work being undertaken by carpenters; of the use of nail guns in manufacturing processes and examination of existing

power hand tools, particularly cordless tools and power tools for driving nails currently available on the market.

Observations were carried out at two work sites: the section of the maintenance workshop at UNSW; and a pallet maker's factory in Lidcombe, NSW. Existing products were examined in power tool shops and hardware shops in the Sydney area.

a) Observation of wood-work being done by carpenters. Aims:To understand and become familiar with nailing techniques.

During visits to the carpentry section of the maintenance workshop in UNSW, the demonstrated the construction of a container with 25 mm by using nails driven by a hammer. The nails used were flat

12 head and 40 mm long. The information collected can be summarized as follows:

Fig.2.1 Photograph of wood-work observed.

Summary of information collected : 1. The claw hammer is convenient for carpenters as the

claw can be used to withdraw bent nails. 2. Flat head nails are used mainly for maximum strength in assembling soft wood and nailing other low

density timbers. 3. The thinner member should always be fastened to the thicker one and 1/3 of the nail should be allowed to

enter the end of the member; for instance, in fastening 25 mm timber, a 40 mm nail should be used. 4. Grasping the hammer in one hand and holding the nail with the other hand is a typical method in starting to drive the nail. This sometimes causes injury to

13 fingers. 5. One ad/antage of using a hammer in wood-work is that

it is used for knocking or banging the timber into place before starting to drive nails.

b) Observation of using a nail gun in manufacturing processes. AimrTo understand the characteristics and become familiar with the use of a nail gun.

Method and nature of the observation. In order to obtain information about the use of nail guns in manufacturing processes, a visit to a pallet makers factory was arranged. During the visit, the renovation or repair of old pallets was being undertaken by the use of a pneumatic nail gun. The pallets were made of 25 mm thick hard wood and 50 mm long round head nails were used. A nail gun was found effective and convenient and considerably increased the work rate beyond that achievable in using a conventional hammer. Information collected on the factory visit can be summarized as follows :

Summary of information collected : 1. Nail guns used in this manufacturing process are powerful. They can fully deliver a 50 mm nail

immediately the operation occurs.

14 Fig.2.2 Photograph showing existing nail

gun being used in a pallet making factory.

Fig.2.3 Photograph showing the deflection of nail towards free edge of timber.

15 2. Operating the gun is convenient and fast. The trigger

switch being pulled simultaneously with the gun being pressed to the work can be seen as an advantage but at the same time it might cause serious injury as a

nail can ricochet from the timber and through the worker's legs. This might occur when the gun tip is placed carelessly, for example close to the free edge

of the timber.

c) Survey of examination of existing power hand tools on

the market. Aim:To obtain information about cordless tools and power tools for nailing and to study of existing designs.

Power tool shops around the Sydney area were visit and the following information was collected.

Summary of information. Cordless tools. Existing cordless tools observed during the survey have

a variety of functions, and they are available with a built-in battery or interchangeable battery pack.

Built-in battery: This feature requires a long charge time of 3 hours or longer. For example, a grass trimmer and a vacuum cleaner both require a 3 hour charge.

16 Fig.2.4 Some existing cordless tools: Built-in battery type.

Interchangeable battery pack: This feature is a recent innovation and it seems to be more advantageous than the previous feature. The tool can be used almost continuously as a spare energy pack is available. Furthermore one battery pack can suit a number of tools in the same range.

Fig.2.5 Some existing cordless tools:

Interchangeable battery pack type.

17 Power nail driving tools. Most existing nail driving tools on the market are pneumatic in operation. They are available in many different sizes and capabilities. For example a small version which is designed for general upholstery, is called a tracker. The largest model available is a heavy duty nailer designed for general purpose nailing, framing, decking and other applications. The nail used is a common nail of up to 83 mm in size.

(a). (b). Fig.2.6 Samples of existing nail driving tool. (a) . Stanley Bostitch tracker model TU20 Series:

- For general upholstery. (b) . Stanley Bostitch air nailer model N80C : For the construction site.

In general, a pneumatic nail gun is suitable only for manufacturing processes as the power source is compressed air which is usually unavailable in

18 households. The air compressor is thus an extra expenditure. The cost of typical nail guns is around

$210, and a portable air compressor unit, of 100 psi, costs around $269.

2.3.3 Literature search. Aim:

To establish the principles of nailing in woodwork. To determine the principles of mechanisms for delivering impact force and the mechanisms of

existing power tools. To establish the engineering principles required in designing power hand tools. To establish the ergonomic principles of designing power hand tools. To identify the Australian Standards which any design will have to meet. To obtain information about existing nail guns. To obtain information about cordless tools.

The nature of the search. In order to obtain all the required information, the search was divided into 7 areas. 1. Wood work. 2. Existing nail guns.

3. Development of cordless tools.

4. Ergonomic principles. 5. Machine design principles.

19 6. Existing mechanisms. 7. Australian Standards.

The main source for the literature search was the main library of UNSW and Faculty libraries in Architecture and Mechanical Engineering. The Physical Sciences

Library was found to contain most of the required information and it has a facility for inter library loans through which publications outside UNSW can be obtained.

Summary of literature search. Information obtained from the literature can be summarized as follows :

1) Wood work. Data was located on techniques and principles of nailing with , types of nails, hammers and their uses, characteristics of wood and also data on previous experiments regarding the force required to drive nails into different kinds of wood. Relevant publications are listed in the bibliography. The most significant publications are Elementary Principles of Carpentry by T.M. Tredgold, and Design and Practice of Joinery by

J. Eastwick-Field. These publications are discussed in detail in the next chapter.

2) Existing nail guns.

Information was identified in text books and journals

20 such as Building; Building Trades Journal; Carpentry and Product Engineering etc. These contained information on the characteristics and specifications of tools and discussions and recommendations about their features. The literature documents many examples of pneumatic nail guns but only a few examples of explosive power and electrical ones. But a similar tool, the gun, is available in pneumatic and electrical form. More details of this tool are given in chapter 3.

3) Development of cordless tools. Cordless tools have only been on the market since 1969. Many varieties have been advertised and written about in trade magazines. Common headlines for articles and advertisements include: " Go anywhere tools pack power"; " The convenience of cordless tools makes them more common than ever". Reduced charging time is another new development that is described. Now it may take only one hour to charge a tool whereas it might have taken 10 to

16 hours for earlier models.

4) Ergonomic principles. There are many sources of publications on ergonomic principles and their application to hand tools. These include, Human Factors in Engineering and Design by E.J. McCormick and M.S. Sanders; Ergonomic Principles in the Design of Hand Tools by T.M. Fraser and Fitting

21 the Task to the Man by E. Grandjean.

According to McCormick and Sanders, the major principles

of hand tool design should be related to the biomechanics of the human hand. They involved the

maintenance of a straight wrist and the avoidance of repetitive finger action. ( McCormick and Sanders, 1987 ). Similar concepts are also dealt with by Fraser, as well as guidance on practical applications such as, for example, the characteristics of handles for specific tools, the size of tools, etc. ( Fraser, 1980 ) .

Grandjean also discusses the dimensions of the hand and the confidence interval as part of the consideration of

body size. ( Grandjean, 1982 ) . The details of ergonomic principles are specified in chapter 4.

5) Machine design principles. Information on machine design such as manufacturing processes, the characteristics and the application of springs, gearing, cam and bearings, was found in three major texts: Design of Machine Elements by M.F. Spotts; Materials and Process in Manufacturing by E.P. DeGarmo; and Gear by P.S. Houghton.

6) Existing mechanisms.

A study of existing mechanisms, especially mechanisms for generating impact, drive, vibration and transmission, was found in Mechanisms in Modern Engineering Design by 1.1. Artobolevskii, Multiplying

22 Human Force out-put : Spring loaded impact tool by C.W. Suggs, G.T. Roberson and B.W. Maw; Mechanics___ of

Machinery by C.W. Ham and W.C. Rogers. Diagrams or detailed drawings of the relevant mechanisms plus their characteristics are given in these publications.

Relevant mechanisms are discussed in chapter 4.

7) Australian Standards. The relevant Australian Standards are listed in chapter 6.

2.3.4 Experimental and mock up testing. Experimental testing of the nailing process, of the spring force for driving nails and the testing of mock ups of various designs were carried out in order to explore issues such as the energy required to drive nail into wood, the spring impacted force required to drive nails and the performance of design mechanisms.

Aims: To establish the factors involved in driving nails.

To investigate the relationship between impact force and the number of blows required to finish driving a

nail. To establish the efficient impact force for driving

nails . To investigate the relationship between size of nail

and number of blows needed to drive the whole length into wood.

23 To investigate the effect of wood type and direction of on the number of blows required to

completely drive in a nail. To investigate the driving of nails by spring force. To investigate the effect of size of spring on the number of blows required to drive nails.

To investigate the possibility of constructing a modified spring load actuated tool with a stored

energy of 4 Nm. To investigate the possibility of introducing a repeating action version of the modified spring load actuated mechanism.

To investigate the possibility of a modified spring load actuated mechanism.

Method and nature of the search. Simple instruments for the tests were constructed in the Faculty of Architecture laboratory. There were 5 experiments using 4 mock ups. The detailed methods and results of the tests are documented in chapter 5.

The experiments were based on engineering principles and were conducted in series as the results of each experiment affected the conduct of the next experiment.

The tests were undertaken in consultation with staff of the School of Mechanical Engineering at UNSW.

Conclusions of the experiments and mock up testing : Impact force or driving energy is the major factor of

24 driving nails. Nails can be driven by spring force. A spring load actuated tool can be modified to be power driven

An existing cordless tool (cordless driver/drill MAKITA 9.6 v) can be used as a power source for driving a spring load actuated tool.

2.3.5 Consultation with engineering experts. Engineers of the School of Mechanical and Industrial

Engineering and an advisor in the Department of Industrial Design at UNSW were consulted. Information obtained included ideas on the methods of experimental

testing, manufacturing techniques, selection of suitable machine elements and the technical assembly of parts.

2.4 Design process. Once the requirements of the design were clearly defined, a number of design concepts based on various design criteria were explored using presentation media such as line sketches, rendered sketches, full scale mock ups and engineering drawings. The most suitable design concepts were selected and developed in more detail. From these concepts one design evolved and was presented as a fully finished full-size model supported by working models. Engineering drawings and rendered sketches of the final design are also included in the presentation.

25 CHAPTER 3

NAILING IN WOODWORK

3.1 Introduction. -4 * Nailing is a common method of fastening, especially for

woodwork and is generally found to be more advantageous

than other methods, as it is simple, quick and cheap.

Normally, the tool for nailing is a hammer, but in

recent years specialized tools including power tools

have been designed and used.

3.2 Principle And Practice.

Driving a nail with a hammer is a skilled task and for non-skilled persons, it may be difficult to achieve good results without practice. There are several requirements

for driving nails successfully.

Fig. 3.1 Nailing with hammer : Swing

the hammer freely and strike the head

squarely on the nail.

26 It is necessary to select a hammer of sufficient weight for a particular nail and timber and to grip it near the end of the handle and swing it freely. The head of the nail needs to be struck squarely and with sufficient force to drive the nail home. Tapping at the nail with short light strikes should be avoided. ( Capotosto,

1979). A second technique is to cease striking when the nail is still a couple of millimeters proud of the surface and finish off with a punch, which will avoid bruising the wood. ( Kay, 1946). Dovetailing the nails, that is, driving them in at a slight angle in alternate directions, will provide more strength in .

( Hayward, 1974 ). Splitting the timber is one of the most common failures in nailing, especially when nailing too close to the edge. To avoid this, it is advisable to pre-drill the entry-point for the nail or to blunt the top of the nail. Blunting the nail or flattening its point will allow the nail to punch, rather than pierce, the wood. ( Leadbeatter and Keable, 1974 ). When nails are driven into end grain they should be skewed towards each other.

There is less danger of splitting in thus crossing several row of fibres and the nails hold much better. ( Ellis, 1987 ).

Driving nails into hard wood can be assisted by using a lubricant on the nail, such as grease. Many carpenters find it convenient to run the nail through their hair a few times, as the natural oils in their hair will

27 pent flattened to punch way through f*pres

Fig*3.2 Showing techniques in driving the nail. (a) . Dovetailed or angled nailing gives greater holding power. (b) . Blunting or flattening of a nail allows the nail to be punched through the timber fibres without separating them. (c) . Toenails should be driven at an angle about 30 degree to the piece. provide lubrication enough to drive the nail successfully. ( Leadbeatter and Keable, 1974 ).

Sometimes toenails, nails driven at a slant to the surface, must be used for framing flooring. These should be driven at an angle of about 30 degrees to the piece and approximately 1/3 of the nail's length should enter the end of the member. ( American Institute of timber

. \ construction , 1966 ).

3.3 Percussive force. In order to investigate the required force for driving a nail (the percussive force), a number of experiments

28 have been conducted by previous researchers. Tredgold found that " The percussive force required to drive the common sixpenny nail to the depth of an inch and a half into dry Christiana deal using a cast-iron weight of 6.275 lbs. was four blows or strokes falling freely through the space of 12 inches; and the steady pressure to produce the same effect Mr. Bevan found to be 400 lbs." ( Tredgold, 1890 ).

There are several factors which affect the percussive force required to drive a nail, including type of wood and direction of driving into the grain. In Elementary Principle of Carpentry Tredgold describes these factors :

" A sixpenny nail, driven into Dry to the depth of

1 inch across the grain, required a pressure of 327 lbs. to extract it. The same nail driven 2 inches endways into dry

Christiana deal, was drawn out by a force of 257 lbs.; to draw it when driven only 1 inch, under like circumstances required 87 lbs. " ( Tredgold, 1890 ). The following results were also obtained by Tredgold : " The progressive depths of a sixpenny nail into dry Christiana deal by simple pressure were as follows : 1/4 inch, a pressure of 24 lbs. 1/2 inch, a pressure of 76 lbs. 1 inch, a pressure of 235 lbs. 1 1/2 inch, a pressure of 400 lbs. 2 inch, a pressure of 610 lbs." ( Tredgold, 1890).

29 3.4 Types of Nail and Their Uses. Nails are the most common mechanical fasteners in

joinery and carpentry and have been known and used since

Roman times . In those times nails were forged from pure iron, but nowadays they are made from drawn steel wire. They can be manufactured from many different kinds of

steel for special purposes. For example, for external and marine application, nails are made from copper,

silicon, bronze and monel metal. ( Leadbeather and Keable, 1974 ).

However, generally nails are made from cold drawn, low carbon steel with a phosphorus and sulphur content not exceeding 0.06 percent in each case. ( AS.2334 -1980 ). They are two systems for describing the size of nails. The old system indicated size by number of pennies. It

is believed that this terminology was derived from the weight of 1000 nails. For example, one thousand 10-penny nails would weigh 10 pounds. Another source suggests

that penny designations date back to the time when nails were described by their price equivalent. The example is given of a one and one quarter inch nail being priced at four pence per hundred and becoming known as a four penny nail. (Leadbeather and Keable, 1974). The shortest nail in this system is the 2d (two penny), which is 1 inch long. The longest is the 60d (60 penny) which is 6 inches long. (Oberg, 1985). The other system is the metric system which is used in the Australian Standards. In the metric system, nails

30 are described by the diameter and the length of shank in millimeters. Examples are: flat head nail, 1.25 mm dia.* 15 mm; bullet head nail, 5.6 mm dia. * 150 mm etc.

Types of Nails.

There are many types of nails used in woodwork. They come in different shapes of head, size, material and finished surface. Each type is designed to suit a particular purpose, such as, indoor or outdoor uses, fixing soft timber, hard timber or soft sheet metal and roofing construction. In recent years, as power driven tools have been designed and increasingly used, certain special types of nails have been designed. Current nail types are as follows : 1. Bullet head nails. 2. Flat head nails.

3. nails or panel pins. 4. Wall board nails. 5. Cement sheet nails. 6. Flex sheet nails. 7. Soft sheet nails. 8. Clouts. 9. Plaster board nails.

10. Decking nails. 11. Duplex nails. 12. Roofing nails.

13. Fencing staples. 14. T-nails. 15. Half-head nails.

31 ill 1.1.Y l lit All N vil S ;\ ;^Qnmc L“2 L.— . JXSJ

i i a r him) s am s * ^[j)iniiiz: 3 K I IV L-

UAH DUD AI4I# N AII s lU^rpumc ,--Z=)'[ t—i \ * | „ 1 :;k

,/N WAl l IIO \I(I) NA11 s lcz=s> \\ ,i ____ !T. ..--- 1 00* npprox **

C'KMKNT SHKKT NAll S vj ------icT'X..----

, iSO'oppro* KI.KX SHKKT NAILS t:'4{l01111 * b -Y M.n ~

Jo >-v

7.9 hi. 0.0 UTS

______2.Ci_M.-a„

Pl.A.STKItnOAKO NAILS

Fig. 3.3 Types of nail.

32 The first two of these types, the bullet head and the flat head nails, are very widely used for general purposes and only the last two types, T-nails and half­ head nails, are designed especially to suit power driven tools.

The bullet head nail.

This has an integrally formed deep, circular, barrel­ shaped head with a flat top surface and a plain cylindrical shank. The bullet head nail is mainly used in application and flooring construction. It is usually driven approximately 2 to 3 mm. below the wood surface with a punch and the holes are stopped with putty for painted work, or colored stopping for polished work. The smallest size of the bullet head nail is 1 mm dia. * 12 mm and the biggest one is 5.6 mm dia. * 150 mm. ( AS 2234 - 1980). The flat head nail. This has an integrally formed thin, circular head with a flat top surface in which the bearing surface of the head may either be parallel to the top surface or be slightly countersunk. The shape of the shank is plain cylindrical . The size of flat head nails ranges from 1 mm dia. * 12 mm to 5.6 mm dia. * 150 mm . In general, the diameter of the head is approximately 3 mm bigger than the diameter of the shank; for example, in the 1.6 mm dia. * 25 mm Flat head nail, the diameter of the head is between 3.8 mm to 4.2 mm .( AS. 2234 - 1980 ).

The flat head nail is used mainly for maximum strength

33 in assembling framing and nailing other low

density timbers and materials where the bullet head would tend to pull through the soft timber. ( National

Building and Construction Industry Training Committee, 1985 ).

T-nails.

These are made up in strips and held together with plastic bands. T-nails are available in sizes from 13 mm to 70 mm in length with a shank diameter of 1.20 mm to 2.5 mm. T-nails may be used for finishing purposes, as the head can be driven below the wood surface easily when they are driven with the head in the direction of the grain of the timber. ( Barrington, Mylius and Arden,

1988 ).

Half-head nails.

These are made up in strips by placing the head to overlap with the nail in front of it. They are available in smooth and ringed shanks and the sizes range from 32 mm to 100 mm. Half-head nails are used in building construction work. ( Barrington, Mylius and Arden, 1988).

3.5 Nail Driving Tools

3.5.1 Hammer

The hammer is a driving tool which consists of a steel head fitted on a handle normally made of wood, but fiber glass handles and steel handles are also available.

34 ( Scott, 1980 ) . It is mainly used to drive nails to fasten timber together. Hammers come in a wide range of

shapes and sizes which are suitable for particular jobs, such as the claw hammer which is most widely used in carpentry, the Warrington hammer which is suitable for

starting small nails , etc.

Fig. 3.4 Types of hammer.

(a) . Claw hammer. (b) . Warrington pattern hammer.

(c) . Ball-pein hammer.

(d) . Hatchet hammer.

(e) . Engineer's hammer. (f) . Soft-face hammer.

The claw hammer. The claw hammer has a striking face to drive in nails and a claw to withdraw bent or unwanted nails. The size of a claw hammer is specified by the weight of the head.

35 The general range of head size and their applications are as follows:

1. 450 gram and 570 gram. : This range is suitable for

general shop work and on-site fixing.

2. 620 gram and 680 gram. : This range is suitable for timber frame construction and general building site operations. ( Harris, 1977 ).

The warrington pattern or cross-pein hammer. This hammer is a light joinery hammer which has a cross pein. The cross pein is suitable to start small nails and to drive nails into corners where a round driving face cannot reach.

Warrington pattern hammers are available in sizes ranging from 170 gram to 450 gram, but the most suitable size for most shop work is 350 gram. ( Barrington,

Mylius and Arden, 1988 ).

3.5.2 Pin-push.

Pin-push is a small nail driving tool. It is designed to be manually activated and to be capable of driving small nails. It is useful in awkward places, which are unable to be reached with a normal hammer, and it is convenient as the magnetic tip will hold the nail even upside down. The method of using pin-push is simply to drop the nail into the sleeve and press down on the handle until it makes an impact.

36 Fig. 3.5 Pin-push. The characteristic of the pin-push is that it is a spring actuated impact tool which is similar to the spring loaded center punch and the hand actuated spring loaded staple gun. The tool consists of an outer tube, a mass supported on a movable central shaft and a compression spring. To operate the tool, the outer tube is pushed downward so the shaft and mass move upward and at the same time the spring is compressed. At the end of the stroke a latch which is attached to the outer tube is released allowing the spring to accelerate the mass. The impact is delivered by the mass being pushed onto the upper end of the shaft.( Scott, 1980 ).

3.5.3 Pneumatic nail gun.

The pneumatic nail gun is a compressed air tool for nailing which is suitable for heavy duty use, such as in manufacturing processes and building construction, rather than for house-holder duty. It is a powerful tool and is significantly faster to use than conventional hammers. However, it is a dangerous power tool and may cause serious injury to the user or nearby people if

37 accidental firing occurs or if nails fly off the work piece.

The power source for the pneumatic nail gun is a supply of compressed air via a flexible hose. This can be provided from a fixed installation, or in conjunction

with a portable air compressor. There are many models of pneumatic nail guns, but their characteristics are similar. When operating or pulling the trigger switch, the compressed air actuates a piston which will strike freely against the nail head. Existing pneumatic nail guns can be considered in 3 groupings categorized by the

design of the nail storage and the nail type used. 1. Round nail magazine. A round nail container is attached on the underside of

the barrel of the tool. Nails lie parallel to and separated from each other. They are kept in position by having fine wire welded to them. As the heads of the nails do not touch each other, it is possible for them to be round head nails.

2. Nail magazine inclined to work piece. Nails used in this type of magazine can be round head

and half head nails. The head of each nail overlaps with

the nail in front of it, so the axis of the strip or

clip is not at right angles to the nail shank. In the case of half head nails the shanks can be much closer together than with round head nails where the shanks must remain separated by almost the whole width of the head.

38 Fig. 3.6 Existing pneumatic nail guns.

(a) . Nail magazine is round.

(b) . Nail magazine is inclined to work piece.

(c) . Nail magazine is parallel to work piece.

39 3. Nail magazine parallel to work piece.

With a nail magazine that is parallel to the work piece,

T-nails or staples are used The head and shanks are

attached to each other and form a straight row since the

head is no wider than the shank on the side where they

touch.

3.5.4 Explosive powered nail guns.

Explosive powered tools are widely used in the building

industry. They are used for fastening into hard

materials such as concrete, brickwork, and structural

steel. Explosive charge Energy transferred

Fastener

(a) .

Fig. 3.7 Diagram showing principles

of explosive powered nail gun.

(a) . High velocity type.

► (b) . Low velocity type.

There are two types of explosive power tools available:

high velocity direct action tools and low velocity or piston operated ones. The characteristic common to both

types is that they force nails or studs instantaneously

into the material. As the explosive power tool is powerful and dangerous so in some states it can only be

40 used by a qualified operator and is subject to stringent safety requirements.

The main causes of accidents from the use of explosive nail guns are: careless handling of the tool. firing of projectiles into unsuitable target materials. ricochets of the nail from the surface or the

interior of the target material. projection of debris of the target material or of

parts of the nail or cartridge case. the firing of projectiles whilst unauthorized persons

are in the firing zone.

( International Labour Office, 1971 ).

In recent years, a new type of nail gun has been developed by Paslode of Lincolnshire,Illinois, which is powered by a mixture of butane and propane and a battery. ( Building Today, Nov. 1987 ).

The functioning of the gun is just like the internal combustion engine of a car. The explosion forces a piston along a cylinder. The piston connects directly to a brad which hits a nail on the head and forces it into the timber. This type of nail gun has an operating speed of 1000 nails per hour and the nails used are 50 mm to

75 mm in length and come in a strip.

41 Fig. 3.8 Showing the new type of nail gun :

Internal combustion using mixture of butane

and propane.

Other special purpose nail driving tools have been designed and used in building construction, such as the automatic strip-floor nailing machine. Unfortunately, this tool is rarely found and there is very little available information on it. ( Capotosto, 1979 ).

Fig. 3.9 Showing the use of a special purpose nail driving tool: The automatic strip-floor nailing machine.

42 3.6 Conclusion. Current methods of driving nails have clear drawbacks. Hammers may cause injury and are often too slow or inconvenient for certain tasks. Nail guns overcome some of these problems, but they may cause more serious injury if ricocheting occurs and they are generally unsuitable for householders who cannot normally obtain the required compressed air. The design of a new power tool was therefor undertaken which would fulfill the common requirements of nailing woodwork, which would be easy to use and completely effective and which would, above all, be safe to operate.

43 CHAPTER 4

SUMMARY OF ENGINEERING FACTORS

In this chapter, the engineering factors involved in the design of a cordless nail gun will be defined and summarized. Two categories of factors are involved : ergonomic principles and design mechanisms.

4.1 Ergonomic Principles.

Summary of ergonomic requirements for designing power hand tools.

1. Force is exerted most effectively when hand and

handle interact in compression rather than shear.

Hence, it is better to exert a thrust perpendicular

to the axis of a cylindrical handle than along the

axis. (Pheasant, 1986).

Tb

A B

Fig. 4.1 Showing shear(Fa) and thrust(Fb)

force on cylindrical handle.

44 2. Bending of the wrist can reduce the effective gripping force and increase fatigue, so the handle should maintain the neutral position of the wrist in which the axis of the rod gripped firmly in the hand

makes an angle of 78 degrees with the axis of the fore-arm. ( Fraser, 1980).

Fig. 4.2 Showing the neutral position

of the wrist. 3. A cylinder shaped handle is found to be most comfortable to grip since there are no sharp edges

which can cause pressure hot-spots , but it does not help maintain orientation. A rectangular section handle is more advantageous in this respect, but will

be less comfortable. The rectangular shape should therefore be modified to have rounded edges, such as ► in a pistol grip.

4. Handle circumference and length should suit the average hand size of the population involved, aiming to maximize the contact area, minimize unit pressure

and offer grip strength. According to Fraser the recommended dimension for power grip is 25-40 mm in diameter, as it was found that the grip force at 50

45 mm is only 95 % of that of 40 mm and also that grip

force at 65 mm is 70 % of 40 mm. ( Fraser, 1980 ).

25mm i to 40m

Fig. 4.3 Diagram showing the recommended dimension of handle for power grip. 5. The length of the handle, for a power grip, must be sufficient for all four fingers. The anthropometric

estimates for a hand with the metacarpal breadth of a large man ( 97.5 th percentile ) is approximately 102 mm. Thus 102 mm is the recommended length of the handle. ( Fraser, 1980 ).

102 mm Metacarpal Breadth

Fig. 4.4 Showing anthropometry of hand.

6. Placement of handle should be directly under the

center of gravity in order to minimize unnecessary

46 torque while holding, positioning and pushing the

tool into the work piece. If the tool is heavy, a

secondary supportive handle should be provided and

the placement of the two handles should give good

support to the center of gravity. ( Greenberg and

Chaffin, 1976 ).

4.2 Design Mechanism.

4.2.1 Summary of some existing mechanisms for striking or similar functions.

1. Hammer action mechanism. Spring

Striker

2. jj

Fig. 4.5 Showing hammer action mechanism.

( From Department of Employment and Industrial

Relations, 1985).

This mechanism is used in impact drills and hammer drills, in order to add percussive force to the drill bit independently of the force provided by the operator.

When the tool holder rotates, the striker moves backward and compresses the impact spring. As the tool holder continuously rotates the pair do not mesh and the impact is delivered.

47 2. Spring load actuated mechanism.

Application of the spring load actuated mechanism has been used in many products, such as staplers, spring load center punches, pin-pushes and plant feeding equipment. The major advantage of the mechanism over conventional impact tools is that the out-put tool can be positioned before impact occurs. ( Suggs, Roberson and Maw, 1979) .

rwv\Av\\\\\\\y\ \ \ -y

OUTPUT TOOL LATCH latch RELEASE IMPACT SPRING

< xjrx:

RETURN SPRING

Fig. 4.6 Construction details of spring

actuated impact tool.

The tool consists of an outer tube, a mass supported on a movable central shaft, a compression spring and an output tool fitted to the end of the shaft. To operate ► the tool, the outer tube is pushed downward so the shaft and mass move upward and at the same time the spring is compressed. At the end of the stroke a latch which is attached to the outer tube is released allowing the spring to accelerate the mass. The impact is delivered by the mass being pushed onto the upper end of the shaft. ( Suggs, Roberson and Maw, 1979).

48 3. Portable electric hammer mechanism.

Hammer head Electromagnets

Striker

Fig. 4.7 Diagrammatic representation

of portable electric hammer mechanism.

The impact is caused by the acceleration of a mass

(striker) brought about by the action of the two electromagnets. As the electromagnets are activated by

AC current, they function alternately thereby producing a continuous backward and forward motion by the striker.

This creates repetitive impact. ( Fig. 4.7 to 4.11 are taken from Artobolevskii, 1979 ).

4. Cam mechanism of a punching press.

Cam Plunger Spring Punch

Fig. 4.8 Diagrammatic representation

of cam mechanism of a punching press.

When the cam rotates, the plunger reciprocates, compresses the spring and strikes the punch. So it pierces one hole on the stock at each revolution of the cam.

49 5. Three link cam mechanism of a punching press.

Fig. 4.9 Diagrammatic representation of a

three link cam mechanism of a punching press.

Impact is caused as weight is allowed to drop when lobes a of cam are not in contact with follower. As the cam rotates the lobes raise the weight again. There are

2 impacts per revolution.

6.Air hammer mechanism with slide-valve air distribution

Piston Hammer head Slide vale Compressed air

Fig. 4.10 Diagrammatic representation of

air hammer mechanism with slide-valve

air distribution.

At the working stroke, the piston moves forward, being of pushed by compressed air at the right end of the

50 cylinder and allowing the air in front of the piston to

escape into the atmosphere by a slide valve. This produces one impact. At the end of the working stroke,

the slide valve is shifted, therefore the piston is

forced to move backward. At the end of the return

stroke, the slide valve is reversed and this begins the

•4 working stroke.

7. Air hammer mechanism with piston air distribution.

Piston Hammer head . Compressed W air 1Y///SS/ ’OA'r\ . . /■'S/ '' it %

Port a

Fig. 4.11 Diagrammatic representation of air hammer mechanism with piston air distribution.

At the beginning of the working stroke, the compressed air enters at the right end of the cylinder and the air in front of the piston can escape through port a, so the piston moves forward and makes impact on the hammer head. At the end of the working stroke, port a is blocked and port b is opened, therefore the piston is forced back. At the end of the return stroke, port f is re-opened and this begins the working stroke.

51 4.2.2 Conclusion.

The design mechanisms surveyed are suitable for different applications and vary in terms of size, amount of energy which can be delivered per impact and the source of energy.

The spring load actuated mechanism appears to be the one most suitable for modification in the design of a new nail-driving tool. The advantage of this mechanism over others is that, firstly, the output tool can be positioned before impact occurs; secondly, the additional energy storage required to give the tool the needed versatility can be obtained by increasing the compressed length of the spring.

Further investigations into the possibility of using and developing this mechanism were undertaken.

52 CHAPTER 5

EXPERIMENTAL AND MOCK UP TESTING

5.1 Introduction. This chapter deals with experimental and mock up testing to investigate the design factors and evaluate

the design. The major objectives of the tests were threefold. The

first was to investigate the basic factors involved in

driving nails; the second was to study the possible use of a spring force in nailing, and the third was to analyze and evaluate the constructed mock ups.

5.2 Experimental Testing of Nailing Principles. The following experiments were conducted in order to investigate the essential factors involved in driving nails. The tests can be divided into 2 categories. The aim of the first category was to obtain general information about the relationship between the factors involved in driving nails. These factors were types of wood, driving force or driving energy, size of nail and direction of driving. The aim of the next category was to investigate driving energy more specifically. A number of tests were conducted using the same driven energy but with different variables. In these experiments, the power source for driving nails

53 was gravitational force. A piece of metal with a certain mass was set at a particular height and dropped to impact on the head of the nail below. The nail was set against a wooden surface, so that it could be driven into the wood. The nail had been driven a few millimeters into the wood beforehand, in order to hold it in position.

5.2.1 To investigate the number of blows required to finish driving the nail into a range of . Three experiments were conducted. The method of all the experiments was the same, involving the dropping of a mass from a certain height to impact on the head of the nails set against the wood below.

In each experiment, three different sizes of bullet head nails, 1.6 mm dia.* 25 mm , 2.5 mm dia.* 50 mm and 3.0 mm dia.* 65 mm , two different kinds of wood, soft wood:

Jeluton and hard wood: Back Bean, and two different directions of driving, along the wood grain and across the wood grain, were used. Driven energy of experiment 1 was 2 Nm, which was the kinetic energy of a free falling mass of 0.250 kg at a height of 0.816 m. In experiment 2, the energy used was 4 Nm which was the dropped mass of 1 kg at a height of

0.408 m. In experiment 3, the energy was 6 Nm, using a mass of 2 kg dropped from a height of 0.306 m.

54 Experiment 1, Experiment 2 and Experiment 3. Characteristics of the instrument and the method of the test.

Fig. 5.1 Photograph showing instruments

of the tests. A guide made of plastic tube of 40 mm dia.* 100 cm was fixed to the stand which was attached to the measuring scale. The nail was pre-driven into the wood a few millimeters in order to hold it in position and placed

55 under the guide. The piece of metal was hung and inserted into the guide ready for free fall.

Before each drop of the mass, the height of the mass from the head was adjusted so that for each drop the energy was constant. The mass was repeatedly dropped until the whole length of the nail was driven into the wood and the number of blows was counted.

56 Summary of Test Results.

( Experiment 1, Experiment 2 and Experiment 3 )

1 i j number of blows for whole length !

1 i

1 dropped j nail * i soft wood i hard wood !

1 energy i size i

1 ( Nm ) i i along i across ! along ! across i

1 i i grain i grain i grain ! grain !

1

1 i small i 5 ! 6 ! 9 ! 12 j

1 2 ! medium i 13 j 18 ! 47 ! 76 i

1 i large i 25 I 50 i 210 i |

1

1 i small i 2 1 3 1 6 ! 8 !

1 4 i medium i 7| 9 ! 24 ! 54 !

1 i large i 10 J 15 j 56 | 140 ** !

1

1 i small i 11 2 ! 4 : 7 i

1 6 j medium i 4 1 5 ! 21 I 47 i

1 1 large i 8 ! 10 j 39 | 102 ** !

Note * Small nail : 1.6 mm dia.* 25 mm.

* Medium nail : 2.5 mm dia.* 50 mm.

* Large nail : 3.0 mm dia.* 65 mm.

** Wax was applied to the shank of the nail.

57 Conclusion.

The number of blows varied as the parameters were changed. The following conclusions were obtained :

1. The number of blows was found to be minimum when

driving the small nail into soft wood along the wood

grain. For example, using a driving energy of 6 Nm,

it took only one blow to drive a small nail into soft

wood along the wood grain while it took 102 blows to

drive a large nail into hard wood across the wood

grain.

2. The driving energy of 2 Nm was found inadequate to

drive a large nail into hard wood across the wood

grain as virtually no penetration of the timber had

occurred by the 200th blow.

3. Driving large nails into hard wood was found to be

easier and with less likelihood of bending the nail

if a lubricant such as wax or grease was applied to

the shank of the nail.

4. In using a specific driving energy, the number of

blows to drive in a large nail was very significantly

greater than the number of blows required to complete

driving in the smaller one. For example, with a

driving energy of 4 Nm, it took 6 blows to drive in a

small nail in hard wood but it took 56 blows to

finish driving the large nail in the same kind of

wood.

58 5.2.2 To investigate the number of blows required to finish driving a nail with driving energy of 1 Nm.

Experiment 4.

Description of the test.

The instrument used was the same as in the previous experiment. But in this experiment, the driving energy was fixed at 1 Nm, which came from three sets of dropped specific masses and heights. They were: a mass of 0.100 kg and a height of 102 cm; a mass of 0.250 kg and a height of 40.8 cm; and a mass of 0.500 kg and a height of 20.4 cm. The nails used were of one size only : 2.5 mm dia.* 50 mm and soft wood : Jeluton was used along the grain. The number of blows required in each case was recorded.

Summary of the result of the test.

( Experiment 4. )

number

energy mass nail size wood direction of

( Nm ) ( kg ) drops

! 0.100 i i i i 7

1 ! 0.250 ! medium i soft !across grain! 7

! 0.500 ! i i i 8

59 Conclusion.

The number of blows required to finish driving the nail of a particular size with the same energy was found to be equal even though the driving mass was different.

5.3 Experimental testing of spring force for driving nails.

Experiment 5.

Aim:

1. To investigate the possibility of driving nails with

a spring force. ( The principle of the pin-push )

2. To investigate the effect of size of spring [ spring

constant ( K )] used for driving nails.

Characteristics of the instrument and the method.

Two instruments were constructed for the test. Their principles and characteristics were the same. They consisted of a compression spring, a metal mass, a guide made of metal tube, a lock and a pushing arm. The difference between the two instruments was the size of the spring and the compressed distance. The spring used in the first tool had a spring constant ( K) of 2177 N/m and a compressed distance of 30 mm. The second one had a spring constant ( K ) of 21428 N/m and a compressed distance of 10 mm. The stored energy of the two tools was the same, 1 Nm.

60 Fig. 5.2 Photograph showing the instrument of the test.

Method. - Lock the mass to the tube. Compress spring by pushing the pushing arm and

locking it at the marked position. The first tool would lock when the compressed length was 30 mm and the second tool would lock when the compressed length was 10 mm. Set the nail on a piece of wood and place it against the front end of the tool.

Release the lock to allow the spring to force the

61 mass to impact on the head of the nail and repeat the

cycle until the nail has been driven completely into

the wood.

Summary of the result of the test.

( Experiment 5 )

i spring j i i wood ! i number !

!constanti energyi nail size i type i direction i of !

! ( K ) | i it i j blows !

! 2177 | 1 ! medium ! soft ! across ! 8 !

! N/m i Nm i j j grain j |

! 21428 ! 1 i medium i soft ! across i 8 !

! N/m ! Nm ! 1 j grain i |

Conclusion.

It was possible to use a spring force to drive the nail and the result was similar to the dropped mass method of the same energy. The number of blows required to drive the nail in completely was exactly the same for the two instruments. It can be concluded that the spring constant or the size of the spring did not affect the result in driving the nail if the stored energy was the same.

62 5.4 Testing of mock up. 5.4.1 Mock up number 1.

Aim : To investigate the possibility of a repetitive action

modified spring load actuated mechanism.

Fig. 5.3 Photograph showing mock up number 1. Description of Mock up number 1. The test mock up consisted of 3 main parts : A spring actuated mechanism which provides energy to impact nails; A cam mechanism which transformed the angular motion to linear motion and also provided the automatic repetitive movement and an electric motor to provide mechanical power to drive the tool.

The mock up was designed so that when the power was turned on the motor would drive the cam, and the follower, which was a part of the spring actuated

63 mechanism, would slide forwards and backwards. On the forwards slide the compression spring was compressed until impact occurred at the end of the movement. The

follower then slid back and reset the spring actuated mechanism. Energy was released and stored alternately,

according to the cam motion and the speed of impact depended on the speed of revolution of the cam. In this mock up, the motor was an 250 volt AC motor. The cam was made of wood with a total displacement of 24 mm ; the spring had a normal length or rest length of 80

mm and a spring constant (K) of 5922 N/m; the latch was released by a separate cam plate.

Results of test. When the power was switched on, the motor started to turn and the cam also started to rotate, but movement

ceased almost immediately because the follower tended to be turned instead of being pushed. 5.4.2 Mock up number 2. As a result of the testing of the first mock up a second mock up was developed.

Description of mock up number 2. Mock up No. 2 was developed from mock up No.l . The cam and follower mechanism were improved by reducing friction. This was done by using linkages, changing the

cam to a metal one and making the contact between the follower and the cam through a roller.

64 Fig. 5.4 Photograph of mock up number 2. A further development of mock up No. 2 was the removal of the electric motor and the cam being driven manually by T-bar handle.

Results of the test. The cam was turned and the follower moved forward when the T-bar handle started turning. As the follower moved, it compressed the spring. Within one half of the cam revolution, the spring was compressed by about 30 mm. and the latch mechanism was released. Then the mass which was placed next to the spring was forced to make the impact.

Then the mass, spring and follower moved backward and the latch locked again as the cam reached the end of the revolution. The action was repeated as the handle continued turning.

65 5.4.3 Mock up number 3. a) Aim:

To investigate the possibility of constructing a

modified spring load actuated tool of stored energy

of 4 Nm.

Fig. 5.5 Photograph of mock up number 3.

Fig.5.6 Photograph showing the detail of mock up number 3.

66 Description of mock up. The principle of the previous mock ups was used for this

modified mechanism. The stored energy of this mock up was 4 Nm. That was set by using a spring which had a

spring constant of 21428 N/m and a compressed distance of 19 mm. The cam plate used had a displacement

distance of 19 mm and contact to the follower through

the ball bearing. The cam shaft was modified to act

as a handle for manual turning. As the cam turned, the follower compressed the spring.

When the cam turned a half revolution the spring was at a maximum compressed stage and at the same time the latch was lever released and the mass was forced to impact on the out-put tool which was assembled at the front end of the mock up. The out-put tool was the means for transferring the impact impulse from the mass

to the head of the nail. As the cam continually turned, the spring depressed and pulled the mass back to the

initial position and the latch lever locked at the end

of the cam revolution. The process or the cycle was repeated as the cam continued rotating..

Summary of the result of try out. The test was successful as the cam could be turned and the mass could be repeatedly impacted on the out-put tool.

67 b) Aim: To investigate the possibility of a power driven version of mock up number 3.

Fig. 5.7 Photograph showing the mock up try out. Method.

An existing cordless tool ( cordless driver/drill MAKITA 9.6 v ) was used for the test. The characteristics of this cordless tool were a 165 watt motor, two speeds, 1100 rpm and 400 rpm and five different fastening

68 torques. The mock up was tested out at both speeds. In the tests the driver/drill was attached to the cam shaft of the mock up, and set on maximum torque.

Summary of the result of try out. In the first test at the high speed ,1100 rpm, the cam of the mock up was not turned when the driver/drill was operating. In the second test with the driver set at the low speed of 400 rpm, the mock up could be operated and the impact force was repeatedly delivered.

c) Aims:

To investigate the efficiency of the mock up in driving the nail. Method.

The cordless driver was fixed to the cam shaft of the mock up. A nail of 2.5 mm dia.* 50 mm was inserted into the

socket and the mock up was pointed at the wood. The wood used was soft wood and in the cross grain direction.

The tool was pushed slightly forward against wood and the driver was operated. The time required to finish driving in one nail was

measured.

Result of the test.

The nail could be driven in completely within 2 seconds.

69 Fig. 5.8 Photograph showing the test.

5.5 Conclusion. The results of the experiment and mock up testing can be summarized as follows : 1. Driving the nail into wood could be achieved using an impact force created by an accelerated mass.

2. The accelerated mass with a stored energy of 4 Nm was found to be sufficient to drive a nail of up to 3.0 mm dia.* 65 mm into hard wood.

3. When driving nails of different sizes, with the same impact force, it was found that the bigger diameter nail needed several blows to finish being driven in

the whole length while the smaller diameter nail needed fewer blows.

70 4. Driving nails into soft wood especially along the wood grain, was found quicker and easier than into

hard wood. 5. Driving the large diameter nail into hard wood was more successfully achieved when wax or some other

kind of lubricant was applied to the shank of the

nail. 6. Accelerating the mass with a spring force was found

to have the same result as accelerating the mass with gravitational force. 7. A spring load actuated mechanism of stored energy of

4 Nm can be constructed and can be powered by an electric motor. 8. An existing cordless tool ( cordless driver/drill MAKITA 9.6 v ) with a speed of 400 rpm was found to be able to drive the mock up of the modified spring load actuated mechanism of stored energy of 4 Nm.

9. Mock up of a modified spring load actuated mechanism of stored energy of 4 Nm powered by a cordless driver/drill MAKITA 9.6 v with a speed of 400 rpm can drive a nail of 2.5 mm dia. * 50 mm completely into soft wood within 2 seconds.

5.6 Implications of the experimental and mock up testing. The results of the experimental and mock up testing were obviously successful in terms of designing the mechanism. From experiment 1, 2, 3 and 4, the results

71 showed that the driving energy of 2 Nm could finish driving a small nail into hard wood in 9 blows or less, while the driving energy of 4 Nm could finish driving the same size of nail in 6 blows or less, and 6 Nm of energy required only 4 blows under the same conditions. Experiment 5 showed that driving a nail could be achieved by using a spring force. Therefore, a spring actuated mechanism of 4 Nm of stored energy could be used for driving nails. The mock up of this design mechanism was therefore developed further.

72 CHAPTER 6

DESIGN

6.1 Design criteria. 6.1.1 Functions. From analysis of the information obtained in previous chapters, especially nailing in woodwork, the functions of the design "CORDLESS NAIL GUN " can be specified as follows :

1. It is a tool for delivering nails into both hard and soft wood, or other nailable materials used in building construction such as hardboard, particle

board, soft sheet metal, wall board, etc. 2. It should be possible to drive nails in any direction, for example downwards or upwards, horizontally, or at a particularly angle to the wood surface such as in toenails or dovetails. 3. It should drive with either the head of the nail

remaining flush or finishing below the wood surface. 4. It should be designed to suit flat or bullet head general wire nails.

6.1.2 Ergonomic aspects. Design criteria based on ergonomic requirements are as follows :

73 a) Design of the handle.

1. The handle should enable a power grip to be applied and should be held with the arm in mid position and

the angle of the elbow at 90 degrees, as the tool is required to be held and pushed against the work piece.

2. The placement of the handle should be such that the tool is balanced in the hand, so the operator does not have to exert force for balancing which causes muscle fatigue. Because of this consideration the handle should be placed in line with the center of gravity. 3. The handle should be held with normal deviation of the wrist. Thus the angle of the handle should be at approximately 78 degrees to the horizontal. 4. The dimensions of the handle should be suitable for

the majority group of users in length, circumference and thickness. Suitable dimensions are as follows : - the length of the handle should be approximately

102 mm. ( Fraser, 1980).

- the diameter of handle should be about 25 to

40 mm. ( Fraser, 1980).

5. The handle surface should not have a sharp edge or any shape or pattern for example grooved, which may cause stress concentration to the palm.

74 b) General considerations. - The weight of the tool should not exceed 4.5 - 5.5

kg. ( Fraser, 1980 ) . - The visual field of user to work piece should be

clear. - The smallest diameter of a finger operated push

button should not be less than 12 mm. ( McCormick, and Sanders, 1987 ). Adequate

clearance for the hand to pass through or the minimum aperture should be approximately 110 mm *

45 mm ( Pheasant, 1986 ). - The moving part of the tool should be designed to be clear of the operator's hand or a safety guard should be provided.

- The force required to operate the tool should be less than 20 % of the maximum static muscular effort. For example , pushing horizontally with the

right hand on a vertical hand grip should be less than 13 N. ( Van cott and Kinkade, 1972 ).

6.1.3 Mechanism Design. With reference to the design mechanisms together with the results of experimental testing, mentioned in the previous chapter, the design criteria for the mechanism design can be summarized as following: 1. Energy of 4 Nm was found to be sufficient to drive

the nail into wood. The experiment showed that with the energy of a dropped mass of 4 Nm it took 9

75 impacts to finish driving a 25 mm dia.* 50 mm nail

into soft wood.

2. It was found that a spring load actuated mechanism

can be used for driving nails and can achieve the

same result as driving with a dropped mass of the

same energy.

3. The spring load actuated mechanism can be designed to

have a stored energy of 4 Nm which is enough to drive

the nail into the wood.

4. The spring load actuated mechanism can be driven by

an electric motor using a cam mechanism.

5. An existing cordless driver/drill of 9.6 Volt is

sufficient to drive the impact mechanism with a

stored energy of 4 Nm.

6.1.4 Standards.

The design of a cordless nail gun should meet the following standards of the Standard Association of

Australia.

AS 1473-1974 Code for the guarding and safe use of

machinery.

AS 1895-1977 Code of practice for the guarding and safe

use of portable electric tools for

domestic use.

AS 2234-1980 Steel nails.

AS 3100-1985 Definition and general requirements for

electrical material and equipment.

AS 3121-1982 Insulating .

76 AS 3160-1987 Approval and test specification of hand held portable electric tools.

6.1.5 Appearance.

It is important that the appearance indicates a perceived value which is in line with the cost of producing the tool.

Some specific appearance considerations are as follows : A dynamic shape is preferred because it implies the dynamics of the tool.

A smooth surface, with rounded corners and edges will achieve comfort in handing and pleasing appearance. There should be a directional emphasis to the design which establishes the direction in which the tool is used.

Because of the potential bulkiness of the tool, detailing should attempt to make it more compact.

6.2 Design Concept.

The design concept has been divided into two parts : design of the mechanism and design of the casing and controls.

6.2.1 Design of the mechanism, a) Designing of the impact mechanism. An objective of the project was to utilize an existing motor, and rechargeable power source. Experiments have

77 shown that the Makita 9.6 v unit was suitable for the mechanical requirement.

Development for the final design.

Aim: To reduce the size of the design so that it would become more compact.

Fig. 6.1 Photograph showing construction

of the design.

78 Fig. 6.2 Photograph showing detail of the design.

Fig. 6.3 Photograph showing detail of the design.

79 Method.

Replacing the impact spring with a shorter one of a

bigger diameter. The spring constant of the original

spring was 21428 N/m and required a compressed length

of 20 mm while the replacement had a spring constant

of 88200 N/m and required a compressed length of 10

mm. The cam plate of the new design was thus smaller.

The displacement distance of the new cam was 10 mm

while the previous one had been 20 mm.

The DC motor, gearing and battery pack ( taken from

cordless driver/drill MAKITA 9.6 v ) was assembled to

the mock up so that it became one integrated unit.

Testing and result :

The test was conducted by the same method as previously and it was found that the result was exactly the same.

It took 2 seconds to drive in one nail.

Fig. 6.4 Photograph showing the mock up try out.

80 b) Design of self feeding and nail holding mechanism.

Concept 1.

To use a mechanism similar to the magazine of self­

loading pistols.

The concept is that the nails can be stored such that the first nail of the row could be placed in the driving

Fig. 6.5 Photograph of a self-loading pistol

and magazine.

Fig. 6.6 Construction of mock up to test

the-concept applied to nails.

81 position while the following nails could be continuously moved upward by spring force to take the place of the

previous one. The difficulties of the design were found to be as follows :

The nails could not be arranged completely parallel in

the magazine because of their heads and they jammed when they started to slide up after the first nail had been

driven in. This difficulty is obvious when the nail is flat head, as the diameter of the head is approximately The first development of the concept.

Fig. 6.7 Photograph of the mock up of

nail magazine. ( 1 st development ).

82 1.6 times greater than that of the shank. The idea was to improve the arrangement of the nails so they could lie parallel and not jam. A solid package was designed which separated the nails so each nail could be held securely and there was no jamming. The disadvantage of the concept was found to be that only a few nails could be placed in the magazine in relation to the size of the magazine. For example, a magazine of 150 mm could contain only 10 nails.

The second development of the concept. The idea was developed to increase the number of nails contained in the magazine by enlarging the size of the previous design.

Fig. 6.8 Photograph of the mock up of

nail magazine. { 2 nd development ).

83 The disadvantage of the design was that the magazine was too bulky because it required double the space as the magazine moved from one position to another and moved up and down after each nail was driven in, in order to position the next nail.

Concept 2.

Using a mechanism similar to a revolver pistol.

Fig. 6.9 Photograph of a revolver pistol.

The nail container had 6 chambers and rotated one sixth of a revolution as the first nail was driven by the ratchet.

The idea was that the nails could be located separately so that a round head did not affect the holding ability and the following nails could be driven consecutively as the roller turned.

The disadvantage of the concept was that the number of nails stored in the tool was limited since it could contain only 6 nails.

84 The first development of the design. The idea was to increase the number of stored nails by enlarging the diameter (of the roller. A roller with a diameter of 100 mm could contain 40 nails.

Fig. 6.10 Photograph of the mock up of the nail magazime. ( 1 st development ).

The disadvantage of the design was that the magazine would become bulky and was wasteful of construction material.

85 The second development of the design. The idea was developed to use a small roller and combine it with a self-loading device so the design would become compact.

Nail at driving position. Magnet roller

Nail

Spring

Fig. 6.11 Design sketch of the mock up of

the nail magazine. ( 2 nd development ).

The roller had 6 semi-circular slots and it was magnetized. The nail container was designed with a spring to push up nails and place them under the roller.

When the roller turned the nail could be picked up and held in the driving position.

The difficulty of the design was that the nail was not held tightly in the so it could easily slip out of position.

86 The third development of the design. Magnet force was rejected in favour of a belt or strip as used in machine guns.

Fig. 6.12 Photograph of the mock up of nail magazine. ( 3rd development ). The nails were held separately in the belt or the strip and the strip or belt was placed against the roller so each groove on half of the roller would be filled with the nails.

The advantages of the concept were : Firstly, the magazine could be compact and contain a great number of nails. For example, a magazine with an overall dimension of 40 mm * 120 mm * 70 mm could

87 contain about 200 nails.

Secondly, general wire nails , even with round heads

could be used as they can be inserted in the re­

usable plastic belt.

c) Final design of the mechanism.

1. The main principle of the mechanism is a spring load

actuated mechanism which is modified to be power

driven by means of a cam mechanism and DC motor.

2. The power source of the tool is a Makita rechargeable

battery pack of 9.6 volt, used in existing cordless

driver/drills.

3. The characteristic of the tool is the application of

a repetitive impact force on the head of the nail so

that it is progressively driven into the work. The

impact energy is 4 Nm and the speed of impacting is

456 rpm.

4. The nail magazine was developed using the principle

of a revolver pistol. The nail which is held in the

plastic belt located against the roller is fed and

positioned when the roller rotates. The roller would

rotate one sixth of a revolution as the tool

completed driving one nail.

88 h— a £ Z cn z < Xo zUJ ou_ o

aio

Zcr> i_u 10CO

Fig. 6.13 Assembly Drawing of mechanism.

89 Diagram showing mode of operation of the design.

Stage 1. Normal position.

Return spring B pushes out-put tool A forward thus

safety switch C is "OFF". Although trigger switch is pulled, the tool will not operate.

Stage 2. Ready for operating.

Pushing the tool against work piece makes the out-put

tool move backward and release the safety switch , so

safety switch is "ON".

90 .© a hail :©io o o o - A i I J 1__ , J 0 5 o dl T*”"" T ♦«" -S 3 . j D (33 :>t

Stage 3. Almost impacting.

Cam plate D rotates when trigger switch is pulled. The

follower E moves forward and compresses impact spring F.

The latch lever is almost lifted by the top part of the

follower.

Stage 4. Impacting.

Cam plate continues rotating. Latch lever is lifted (1)

to allow hammer H to move (2) and to impact out-put

tool, and the nail is driven approximately 5-6 mm into

work piece. The length of the nail entering the work

piece with each impact depends on the type of wood and

size of nail.

91 EXT Eli SI OM SPRIKC-

PUSHING

Stage 5. Repetitive cycle.

The cam plate continues rotating. The follower moves backward (1) and pulls the hammer back to the normal position. The impact spring is now at rest position and the latch is free to drop into the lock position (2). As the tool is being pushed, the repetitive cycle starting from stage 2 will occur , unless the whole nail has been driven in.

92 p Q O O

COUPRESSIOK SPRING

PUNCH Position derail

Stage 6. Completion of action.

The nail is completely driven into the work piece and

the out-put tool is at normal position so the safety

switch reverts to "OFF". The tool is stopped

automatically even if the trigger switch remains

pulled. The nail head can be punched below the workpiece

surface if "PUNCH" switch G is switched downward to

"PUNCH" position. At "PUNCH" position, the safety switch

lies at an angle so the out-put tool goes forward

further before pressing on it and activating it.

93 Diagram showing characteristics of nail-feeding and nail-holding system.

Nail holding device. Stage 1. Ready for driving the nail. Nail No. 1 Nail No.l is at the driving position. Roller It is held firmly on the roller by

Mechanism the holding device. The ratchet for turning roller. device is at the normal position. Ratchet Stage 2. Impacting nail.

While nail No.l is being impacted, the tool moves forward and cam Y ( see Stage 1 of diagram showing mode

of operation ) pushes the ratchet device to move upward. Stage 3. Near completion of driving nail No.l. When the nail is almost driven the whole length, the ratchet is at the

maximum point. It is thus able to catch another tooth of the roller. Stage 4. Nail No. 2 is in driving

position.

As soon as the tool is pulled away

from the work piece, the ratchet is

moved down by the compression spring and the roller turns 1/6 revolution. Therefore nail No.2 is now in the driving position.

94 6.2.2 Design concept of appearance.

Concept 1.

This angle is based normal deviation of Centre of wrist (78 degrees). Gravity.

This area has enough clearance for the hand.

Direction of thrust Battery housing designed graspable dimension. force. to be of

Direction of the tool.

Fig. 6.15 The design sketch of concept 1.

95 The intention was to design in accordance with ergonomic principles. The first consideration concerns muscular effort. As operating the tool requires a thrust force against the work piece, the direction of applied force on the handle should be in the line of direction of the tool. The second consideration was to maintain a straight wrist. So the handle should be at an angle of around 78 degrees to the horizontal. Additionally a guard to cover the movement of magazine is provided to protect the user's hand.

The advantages of concept 1. 1. The exerted force for operating the tool is effective as the direction is in the line of the direction of the tool. 2. It is safe for the user's wrist. As the handle

maintains a straight wrist, it should avoid the tendons being bent and bunching up in the carpal

tunnel which causes Tenosynovitis. 3. The guard to cover the movement of the magazine can

protect the user's hand.

The disadvantage of concept 1. The tool is not balanced in the hand as the handle is not in the line of the center of gravity of the tool.

96 Concept 2.

Auxiliary handle enables This aperture found to be power grip and balance. too narrow and uncomfortable.

Fig. 6.16 The design sketch of concept 2.

The design was fundamentally concerned with the

auxiliary handle and was also based on ergonomic

principles. The power grip with the hand in mid position

provides fully effective force. The angle of the handle

and the guard to cover the movement of the magazine

were similar in intention as in concept 1. ►

The advantages of concept 2.

The tool is balance on the handle ( auxiliary handle )

and the force is exerted effectively through both handles.

97 The disadvantages of concept 2.

The clearance of both sides of the auxiliary handle was found to be inadequately comfortable for the user.

Concept 3.

_____ Motor housing.

Fulcrum. This area may obstruct arm.

Battery housing. Foldable.

Fig. 6.17 The design sketch of concept 3.

The aim was to diminish the storage package and the usefulness of the parts. The battery pack housing had been designed to be a foldable handle so there was no need for the additional mass of handle. As the handle was placed in the line of center of mass of the tool it was balanced in the hand.

The advantages of concept 3.

The tool is compact and light as the handle is foldable and no additional mass is needed. This would be convenient for storing, handling and using it.

98 The disadvantages of concept 3.

The design was found to be lacking in rigidity especially for long use as the handle was foldable. The thickness of the handle was found to be slightly larger than to be easily graspable. This caused discomfort and decreased grip strength.

Another disadvantage was the rear part of the tool obstructed the user's arm.

Concept 4.

This pattern improves dynamic appearance the tool.

Fig. 6.18 The design sketch of concept 4.

The objective was to introduce a dynamic shape into the design, because it seemed to correspond with the function of the product which was the delivery of impact or dynamic force.-

99 Another intention was to make the tool balanced in the hand by placing the handle in the line of center of gravity of the tool.

The advantages of concept 4.

The tool is balanced and also still maintained a

straight wrist. Therefore itwas safe and reduced

fatigue by the user. The dynamic shape applied to the design was found effective in terms of expressing the

function of the tool.

The disadvantages of concept 4.

This design was found to be disadvantageous when there

is a need for an auxiliary handle to exert additional

force to ensure firm handling.

Concept 5. Ventilation.

Suitable for holding as auxiliary handle.

100 Holding at this area Enlarged to be a stop as a form of auxiliary to prevent slip handle. when pushing.

This area can be held and pushed for precision grip.

Fig. 6.19 The design sketch of concept 5.

101 The concept developed from concept 3 in trying to include the auxiliary handle into the design and maintain the balance of the tool. The purpose of this concept was to avoid the attachment of the auxiliary handle so the modification was only on the tool unit.

The advantages of concept 5. The tool was balanced as in concept 3 but it provided more firmness in handling and efficiency of exerted force as the auxiliary handle was included.

The disadvantages of concept 5.

The posture of the hand on the auxiliary handle was found to be ineffective from an ergonomic point of view. The design suggested by ergonomists is to exert a thrust perpendicular to the axis of a cylindrical handle.

Concept 6. The concept was developed from concept 5 by modifying the nail magazine to become an auxiliary handle. This modification should be the solution of the problem of having an ineffective auxiliary handle. It maintained a thrust perpendicular to the axis of the handle.

102 Slope to give clear view.

Jt - —

This point may- cause injury. Nail magazine The body of the was modified tool slides forwards to become an and backwards over auxiliary handle. the magazine during operation.

Fig. 6.20 The design sketch of concept 6.

The advantages of concept 6.

The performance of the auxiliary handle was successful, the force exerted on it was effective as the direction of the force was perpendicular to the axis of the handle. The tool was less bulky as a guard to cover the movement of the magazine was removed to improved grasping.

The disadvantages of concept 6.

The disadvantage of this design is that the user's hand on auxiliary handle/magazine could be injured by rubbing against the main body of the tool. When the tool was in use, the auxiliary handle/magazine would rub against the main body of the tool.

103 Concept 7.

Battery housing can be used as auxiliary handle. This line represents the direction of the tool.

Ventilation.

Horizontal line makes the tool look slender and less bulky.

Fig. 6.21 The design sketch of concept 7.

The intention of the concept was to maintain the balance

of the tool, but reintroduce the guard to cover the

movement of the magazine as it had been found effectual.

The need of the auxiliary handle also seemed to be

essential, therefore further development of this was

required. In this design, the battery pack was formed as

an auxiliary handle and it could be swung to either side

of the tool to suit the preferred hand of the user. When

it was not in use, it could be folded into place so no

extra space was needed.'

The advantages of concept 7.

The tool was balanced as the placement of the handle was

104 still maintained. Also it was safe as the guard to cover

the movement of magazine was maintained. The auxiliary- handle provided an effective exertion of force by the user. The design of the auxiliary handle did not require any additional mass as it was modified from the battery pack housing. Therefore the tool was compact and light and there were no loose parts that could be lost.

The disadvantages of concept 7.

The thickness of battery pack housing is slightly larger than was comfortably graspable. So it is found unsuitable especially for users with small hands.

Concept 8. Mounting for fixing auxiliary handle.

Holes for checking contents of magazine.

This pattern indicates direction and output point of the tool. Centre of

Fig. 6.22 The design sketch of concept 8.

105 This design seemed to be the solution to designing an auxiliary handle. It was designed to be attached on the side of the tool and might be changed from one side to the other to suit the preferred hand. The line pattern appearing on the design made the direction of the tool clear.

The advantages of concept 8. As the guard to cover the movement of the magazine, the position of the handle and the angle of the handle are still maintained as in the previous design, the safety and balance of the tool remained unchanged. The design of the auxiliary handle was effective as it could be easily attached to the tool and it was reversible from one side to the other to suit the preferred hand. The position and shape of the auxiliary handle maintained the effectiveness of the exerted force as its axis was perpendicular to the direction of the exerted force and the exerted force was in the line of the tool direction.

6.3 Design Development.

As the major features of concept 8 such as placement of handle, angle of handle, guard to cover the movement of the magazine and design of the auxiliary handle, were found satisfactory, they were retained in the further development of concept 8 for the final design.

106 The 1st design development.

These area come ■into contact with

a smooth curve is used to increase comfort.

Fig. 6.23 The design sketch of the 1st development.

Smooth curves were designed for the areas which come into contact with the user's arm such as the handle and the bottom part of the tool body. This idea was to increase comfort. The line pattern was carefully applied in some areas to make the tool more pleasing such as the line pattern of the holes for checking on content of the magazine, and the ventilation slots.

107 The 2nd design development.

Instructions included on the design.

Smooth curves improves appearance.

Fig. 6.24 The design sketch of the 2nd development.

The development of this design was to include the instructions in the design. This was for the convenience and the safety to user.

108 The 3rd design development.

Smooth and round

These points also changed to a round shape.

Fig. 6.25 The design sketch of the 3rd development.

This development was to increase the smooth or round shape on the edge and also change the pattern of mounting for fixing an auxiliary handle into the round shape. The reason for this was that the round shape would relate to the smooth, round curve of the rear part of the tool.

109 The 4th design development.

Groove indicates the point at which the nail emerges.

The whole area of the rear part becoming a smooth curve.

Fig. 6.26 The design sketch of the 4th development.

The design was further integrated with engineering and ► psychological requirements. More smooth curves were introduced and the holes for checking on the content of the magazine were made round.

110 6.4 The Final Design.

' Push button for Push button /battery housing lid. for opening nail magazine.

Mails

Mountings for fixing auxiliary handle.

Fig. 6.27 The design sketch of the final design.

The final design was an improvement on the last development. Only minor adjustments were made so that it became nuyre satisfactory in all aspects. A description of the operation was included in the design, namely the nail loading or refilling method, the batterv pack removing and storing feature, the placement and the design of the safety switch and the "PUNCH" switch.

Ill Design specifications.

1. Using all types of nail in which the diameter of the head does not exceed 7 mm and the length does not exceed 65 mm. For example, the biggest size of flat

head nail which can be used is 3.0 mm dia.* 65 mm .

2. Using 9.6 volt "MAKITA" battery cartridge 9000 together with fast charger model DC 9100. The

charging time is 1 hour. 3. Overall length is 374 mm, overall height is 210 mm .

4. Net weight is approximately 2.2 kg. ( with magazine

fully loaded with nails ) 5. Magazine capacity is approximately 200 nails. ( using the biggest nail size )

112 Fig. of 374 m m

the

6.28

design.

Diagram 113

showing o E E

overall

dimension

Fig. 6.29 Photograph showing some of the wooden mock ups. m| Hr | in5lii I 1 .... ’ll i 1 m

I---- js|

Fig. 6.30 Photograph showing some of the rendered

concepts and the color explorations.

114 Photographs of fully finished block model.

115 Fig. 6.31 Photograph showing side view of fully finished block model.

116 Fig. 6.32 Photograph showing end view of fully finished block model.

117 Fig. 6.33 Photograph showing end view of fully finished block model.

118 Fig. 6.34 Photograph showing side view of fully finished block model.

119 Fig. 6.35 Photograph showing side view of fully finished block model.

120 Fig. 6.36 Photograph showing front view of fully finished block model.

121 Fig. 6.37 Photograph showing front view of fully finished block model.

122 Fig. 6.38 Photograph showing PUNCH and safety switch of the design.

123 Fig.6.39 Photograph showing use of tool in horizontal position.

Fig. 6.40 Photograph showing reverse view of tool used in horizontal position.

124 Fig. 6.41 Photograph showing tool used in upward-facing perpendicular position, (as in working on ceiling).

125 Fig. 6.42 Photograph showing tool used in downward-facing perpendicular position, (as in working on floor).

126 Fig. 6.43 Photograph showing method of reloading nail magazine.

Fig. 6.44 Photograph showing simple operation for reversing handle.

127 Fig. 6.45 Photograph showing method of removing battery for recharging.

128 Fig. 6.46 Photograph showing ease of transport of tool by auxiliary handle.

129 Engineering drawings.

130 Fig. 6.47 Engineering Drawing Number NG 001.

131 Fig. 6.48 Engineering Drawing Number NG 002

132 ooooooooo o 0^0 o o o o o o o o

Fig. 6.49 Engineering Drawing Number NG 003.

133 Fig. 6.50 Engineering Drawing Number NG 004.

134 -C u u *-/ U -H U -H -H C * 4~> «J N -ri #1 'H W M J3 O G 1 « i: -h a o w *-• o> e >* M NO H •*-< *-4 H 4-< “ S -o " . i-. C-H

n n ho (T'eohiflin^nNHOff'Mr* va in ^ «n n h o n n n nn nnnmnnnnnnhhh *h r-« »h tH .h »-♦

Fig. 6.51 Engineering Drawing Number NG 005.

135 6.5 Conclusion : Evaluation of final design.

1. The tool is balanced about the main handle. The auxiliary handle enables users to steady the tool and provides operating force. The reversibility of the

auxiliary handle enables it to be used by left and right handed users. 2. The design is satisfactory in ergonomic terms such as

the weight of the tool, the force required for operating the tool, the line of vision from the user

to the work piece, the positioning of the user's hand

while using the tool, the posture of the hand, the dimensions of the control button and the safety guard. 3. The overall dimensions are acceptable for a portable power hand tool. The appearance is well integrated with the essential mechanical requirements. 4. The design covers the major requirements of a nail driving tool. It can drive a general wire nail with both round heads and bullet heads which are up to 65

mm in length. The nail can be driven with the head below the surface or remaining flush to the wood surface by selecting the "PUNCH" switch.

5. The tool is conveniently and quickly loaded. The

nails can be stored and automatically fed by use of a plastic belt. It can be used without the plastic belt

by inserting or feeding nails directly into the tool. The plastic belt is re-usable.

6. The battery pack is easily removed from the tool for

136 recharging. The advantage of the MAKITA 9.6 V Model 9000 battery pack is that it needs only one hour for

fully charging. 7. The instructions provided on the tool enable the operator to understand the tool's mode of operation

and requirements.

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