BASIC MACHINING Foreword MIC has produced this book for us in its Industrial Maintenance Journeyman Programme and it is specifically designed to introduce the basics of maintenance. This book is intended for use as a reference text to be supplemented by notes and explanations and does not stand alone. Compilation of this book was completed with standard published material, Tel-A-Train and resource personnel at MIC. No claim is made to the ownership of any material contained herein. THIS BOOK IS NOT FOR SALE REFERENCE TEXT USED TABLE OF CONTENTS 1. Measurement 3 2. Hand Tools 7 3. Drills and Drilling Machines 22 4. Mills and Milling Machines 24 5. Grinding and Grinding Machines 43 6. Lathes 55 2 MEASUREMENT VERNIERS The Vernier Caliper is one of the most versatile precision measuring instruments available to the skilled metal working craftsman. Most toolmakers and machinists prefer at least one good vernier and a few micrometers foe their own personal use on the job. A Vernier Scale is the name given to any scale making use of the difference between two scales which are nearly, but not quite alike, for obtaining small differences. The difference between the smallest division on the fixed scale and the smallest division on the Vernier or slid- ing scale is the key basis on which the vernier caliper works.this difference is the accuracy of the Vernier. METRIC VERNIERS Vernier (1) On the fixed scale, real standard dimensions are accurately engraved.The smallest division is 0.5mm. On the Vernier scale 12mm is divided into 25 equal parts. The smallest division is therefore 12/25 = 0.48mm. Difference in divisions – 0.50 – 0.48 = 0.02mm. Vernier (2) On the fixed scale the smallest division is 1mm. On the Vernier scale 49mm is divided into 50 parts. The smallest division on the vernier scale is therefore 49/50 = 0.98mm. Difference in division = 1.00 – 0.98 = 0.02mm. ENGLISH VERNIERS: Vernier (1) On the fixed 1” is divided into 10 parts, then each tenth is further sub-divided into 4 parts 1/40 = 0.025. On the Vernier scale 6/10 is divided into 25 parts 6/10 – 25 = 6/10 × 1/25 = 0.024” Difference – 0.025 – 0.024 = 0.001”. Vernier (2) Fixed Scale: 1” is divided into 20 parts = 1/20 = 0.05” VERNIER SCALE: 49 divisions on the fixed scale, (which is 49 × 0.05 = 2.450”) is divided into 50 parts. The smallest division on the Vernier scale is 2.150 ÷ 50 = 0.049” Difference – 0.050 – 0.049 = 0.001” GENERALLY – The accuracy of metric verniers is therefore = 0.02mm. The accuracy of English verniers is therefore = 0.001” 3 HOW TO READ ANY VERNIER SCALE 1. Note the real dimension on the fixed scale which the zero on the vernier scale has already passed. i.e. the number of whole divisions on the fixed scale to the left of the zero on the vernier scale. (These divisions maybe whole millimetres or half millimetres 0.10”, 0.05”, 0.025” depending on how the fixed scale is divided). 2. Locate the line on the vernier scale which coincide exactly with a line on the fixed scale. 3. Check the number of divisions on the vernier scale between the zero and the line which coincides. 4. Multiply this number by the accuracy. 5. Add to the previous noted dimension. This is also applicable to the height gauge. Measuring Exercises. Review Questions. RANGE Internal measurements (error). Provision for setting dividers. Clamp nuts, fine adjustments. 4 VERNIER CALIPER Vernier Calipers are precision tools used to make accurate measurements to within 0.02 mm or 0.001 ins. They consist of an L-shaped bar and movable jaws which are graduated on both sides, one side for taking outside measurements and the other for inside measurements. The bar contains the main graduations and the vernier graduations are on the movable jaw. Limitations arise through application of the vernier caliper due to the fact that they depend a great deal upon the skill and the capabilities of the user. Feel is essential in determining when the jaws of the instrumen5t are truly along the line of measurement. This is especially true with inside measurements, whereby touch and manipula- tions determine when the maximum distance on diameter is obtained. Feel is a necessity in attaining precise measurements, and in addition, undue forces will cause excessive wear or damage to the instrument. Wear and manipulative factors have a direct influence on reliable measurements and one must be certain to read the proper scale. Figure 1. VERNIER CALIPER THE MICROMETER When parts are to be measured to the second placed of decimal in the metric system, or the third place in the English system, the micrometer is commonly used. Sleeve (with main scale) Anvil Spindle Ratchet Knob Lock Thimble (with rotating Vernier scale) Frame Figure 6. MICROMETER 5 WORKING PRINCIPLES AND CONSTRUCTION A spindle with external thread for measuring and internal thread at the end for fixing the thimble to the spindle. The barrel has the internal measuring threads and is a one piece unit with the frame. Over the frame is a thin walled sleeve with the graduations in inches or mm etched longitudinally. This sleeve can be turned with a spe- cial spanner for small adjustment. There is also a nut for adjusting the longitudinal position of the thimble. The ratchet is mounted on the screw which holds the thimble and spindle together and held in position by a small screw. The ratchet slips when a certain fixed amount is applied. This gives consistent readings. The right end of the thimble sometimes called the rim is divided into 50 equal divisions around its periphery. The measuring threads are very accurate and are precision ground with a pitch of 0.5 mm, hence for each revo- lution the spindle moves 0.5 mm. Therefore one division on the thimble is = 0.5 = 1 = 0.01 mm this is the accuracy of the micrometer. 50 100 The barrel is graduated in mmm and 1//2 mm. Reading the micrometer (0-25 mm) (1) Note the number of whole millimetre visible between 0 (zero) on the sleeve and the end of the barrel. (2) Check to see if a 1/2mm division is visible before the end of the barrel on the lower half of the thimble graduations, if so add .5 to the whole mms in (1) (3) Read off from the thimble the amount of hundreds below the horizontal centre mark on the sleeve and add to the previous amount ENGLISH MICROMETERS The measuring threads are 40 T.P.I hence a pitch of 1/40” = 0.025 25 threads The thimble is divided into 25 parts therefore one division on the thimble is = 0.025 = 1 = 0.001 one thread 25 1000 This is the accuracy of the inch micrometer. The barrel is divided (graduated) in 1/10” which is further divided into four parts hence each division is 1/40 = 0.025 Reading the micrometer 0 – 1”. (1) Record the tenths – the numbered lines before the thimble edge (2) Record the amount (number) of division between the last numbered line and the edge of the thimble and multiply them by 0.025. (3) Record the thousandth on the thimble below the horizontal centre mark on the sleeve (4) Add 1, 2 and 3 6 HAND TOOLS FILES A file is a hand cutting tool, made of high carbon tool steel, used to remove surplus metal and to produce a fin- ished surface. Files may be procured in a variety of shapes and types, therefore the student is required to secure the necessary knowledge, not only to distinguish one file from another, but also to determine their particular use. EDGE TANG BLADE TOE HEEL LENGTH HANDLE SHOULDER Length – the distance from heel to toe Body – is that part of the file that does the cutting. It comprises of the faces and edges of the file which are made up of a large number of cutting edges. Heel – is the uncut portion of the file Toe – the extreme end of the file opposite the heel Tang – pointed portion at the end of the heel used for securing handle to the file Note: The length of the file is measured by length of body (exclusive of the tang). CLASSIFICATION OF FILES Files may be divided into two classes: (1) Single cut files Those files have a series of parallel teeth running diagonally across the width of the surface as shown in Fig. 1. This group included Mill Lathe and Saw files. Single cut files are used when a smooth surface is desired or where hard materials are to be finished. (2) Double cut files These files have 2 courses of teeth crossing each other, one course being finer than the other. These rows produce hun- dreds of cutting teeth which makes for fast removal of stock and easy clearing of chips. Both single and double cut files are manufactured in various degrees of coarseness. This is indicated by the terms bas- tard, second cut and smooth. Files are manufactured in many shapes and cross sections. These are indicated by the terms, hand, mill, square, round, half round, triangular etc. 7 FILING PRACTICE Filing is a highly skilled and accurate phase of the machine trade. Skill in filing can only be acquired through constant practice. If the following rules are observed in the early stages of practice filing, the operation will require much less ef- fort and the quality of the finished work will be of higher order.