8. MACHINE TOOL TESTING Sr

8. MACHINE TOOL TESTING Sr. Alignment Test Performance Test No.

01 Various geometrical checks Actual performance of job on are carried out, called as machine tool is called alignment test. performance test. 02 These tests are carried out at These tests are carried out at static condition. working condition.

03 These tests are checking It is checking of jobs, position of components and manufacturing on machine displacement relative to one and its tolerance limits as per another. design. 04 e.g. Alignment of axis of e.g. Manufacturing of job on lathe spindle to saddle lathe. movement. Parallelism Testing • Two lines or planes are called parallel to each other when the distance between them, measured in perpendicular plane remains same or constant.

Parallelism of two planes

• Two planes are said to be parallel, when their distance from each other is measured anywhere on the surface and at least in two directions, and the maximum error (the difference between the maximum and the minimum dimensions obtained when measuring) over a specified length does not exceed an agreed value. The test for parallelism of two planes is carried out in two directions (generally perpendicular to each other). • The dial indicator, which is held on a support with a flat base, is moved in one plane over a given length, and the feeler is made to rest against the second plane ; and the deviations noted down

Parallelism of an axis to a plane

• An axis is said to be parallel to a plane, if the maximum difference between the several readings taken while measuring the distance of line from plane at a number of points, does not exceed a predetermined value. In testing, the feeler of the dial indicator is made to touch the surface of the cylinder representing the axis and thedial indicator (held on a support with a flat base) is moved along the plane by the specified amount (length over which the test is to be performed) (Fig. 7.10). At each point of measurement the shortest distance is found by slightly moving the indicator in a direction perpendicular to the axis.

Parallelism of two axes

• This test is made in two planes, first plane being the one passing through one of the two axes and as near as possible to the second axis, and the other plane is perpendicular to the first one. In this test, the dial indicator is held on a support with a base of suitable shape, so that it slides along a cylinder representing one of the two axes; and the dial indicator is adjusted so that its feeler slides along the cylinder representing the second axis. The maximum deviation between the axes at any point may be determined be gently rocking the dial indicator in a direction perpendicular to the axes. In the same way the parallelism may be tested in the perpendicular plane. Straightness Testing

• A line is to be straight for a given length if variation of distance of its points from two planes perpendicular to the plane of point and parallel to the line remains same within specified tolerance limit. Straight Edge Method

Spirit Level Method

By Autocollimator • In case of measurement by auto-collimator, the instrument is placed at a distance of 0.5 to 0.75 meter from the surface to be tested on any rigid support . • The parallel beam from the instrument is projected along the length of the surface to be tested. • A block fixed on two feet and fitted with a plane vertical reflector is placed on the surface and the reflector face is facing the instrument.

• The reflector and the instrument are set such that the image of the cross wires of the collimator appears nearer the centre of the field and for the complete movement of reflector along the surface straight line, the image of cross-wires will appear in the field of eyepiece. • The reflector is then moved to the other end of the surface in steps equal to the centre distance between the feet and the tilt of the reflector is noted down in second from the eyepiece. • With the reflector set at a – b , the micrometer reading is noted and this line is treated as datum line. • Successive readings at b – c, c — d, d – e etc. are taken till the length of the surface to be tested has been stepped along. Squareness Testing

• Two lines, two planes or a line and plane are said to be perpendicular when the error of parallelism in relation to a standard square does not exceed a given value.

Squareness between axis & plane

• For this test the dial indicator is mounted on an arm which is attached to the spindle representing the axis of rotation. The plunger of the dial indicator is adjusted parallel to the axis of rotation and made to touch the plane. As the spindle revolves, the dial gauge (or the end of plunger if revolving freely into air) describes a circumstances, the plane of which is perpendicular to the axis of rotation. When no testing plane is specified the dial gauge is rotated by 360° and the variation in the readings of instrument represents the deviation of parallelism between the plane of the circumstances and the plane to be tested. However, if planes are specified (e.g. planes 1 and 2) then the difference of the readings in the position of the dial gauge, 180° apart is noted for each of these planes • The deviation is expressed in relation to the diameter of the circle of rotation of the instrument. The effect of periodical axial slip of the spindle can be eliminated by repeating the above test after moving the dial gauge through 180° relative to the spindle and average of two sets taken. The effect of minimum axis play can be eliminated by means of a suitable axial pressure. Between Two Planes • Squareness of two planes 1 and 2 is checked by placing the square on one plane and then checking the parallelism of 2nd plane with the free arm of the square by sliding the dial indicator (mounted on a base) along 2nd plane and its feeler moving against free arm of the square. Between Two Fixed Axes • Fix typical type of square with proper base as shown in figure. • Arrange dial gauge with stand on another axis. • Move dial, which touches the square edge (blade). • Note the readings. • Zero variation shows squareness of two axes. Between One Fixed axis and other Rotable Axes fixed. • The dial gauge mounted on arm and fixed on the mandrel is brought into contact with the cylinder representing fixed axis at two points 1 and 2,180° apart and deviation expressed in relation to distance between 1 and 2. Out of Roundness

• It is defined as the radial distance between the minimum circumscribing circle and the maximum inscribing circle, which contain the profile of the surface at a section perpendicular to the axis of rotation.

Sources of Out-of-Roundness • Several reasons when machining parts can be attributed to cause out-of-roundness. These are clamping distortion, spindle run-out, presence of dirt and chips on clamping surfaces, imbalance, heat and vibration. The characteristic roundness shape varies greatly depending on the method of generation. The tolerance on roundness is critical and it should be much closer (usually five times) than that of the other dimensional tolerance which it effects. Run out

• It is defined related to running of a job. • The job may be rotating with some another centre than its geometrical centre, the distance of such centres is run out.

Measurement of Run out using V-block • The V-block is placed on a surface plate and the work to be checked is placed upon it. A sensitive dial indicator is firmly fixed in a stand and its feeler made to rest against the surface of the work. The work is rotated to measure the rise and fall of the work-piece. For determining the number of lobes on the work-piece, the work-piece is first tested in a 60° V-block and then in a 90° V-block. The number of lobes is then equal to the number of times the indicator pointer deflects during rotation of the work piece through 360°. • Following factors are to be considered while doing experimentation. 1) Angle of V-block. 2) Position of instrument. 3) Number of lobes on the job. For such measurements in laboratory, adjustable V-block can be used. • Ovality – • When a job instead of circular, is having elliptical shape with some major and minor diameters called as Ovality error is present. • Lobbing – • Number of times, because of error in manufacturing, such type of error is created in a circular job. If a inspector measures a circular job at 3-4 places then also, the diameters of such job found to be some. For this only the job is to be checked using proper method for avoiding lobbing errors. Flatness Testing Using Optical Flat • The essential equipment for measurement by light wave interference is a monochromatic light source and a set of optical flats. • An optical flat is a circular piece of optical glass or fused quartz having its two plane faces flat and parallel and the surfaces are finished to an optical degree of flatness. • Optical flats vary in size from 25 mm diameter to about 300 mm diameter.

• If an optical flat is placed upon another flat reflecting surface (without pressure) it will not form an intimate contact, but will lie at some angle 0 making an inclined plane. • If the optical flat be now illuminated by monochromatic source of light, the eye if placed in proper position, will observe a number of bands. • These are produced by the interference of the light rays reflected from the lower surface of the top flat and the top surface of the lower flat through the very thin layer of air between the flats. • S is the source of monochromatic light. At point A, the wave of incident beam from S is partially reflected along AB and is partially transmitted across the air gap along AC. • At C, again the ray is reflected along CD and passes out towards the eye along CDE. • Thus the two reflected components, reflected at A and C are collected and recombined by the eye, having travelled paths whose lengths differ by an amount ACD. • If the path lengths of the two components differ by an odd number of half wavelengths, then condition for complete interference is achieved. • If the surface is perfectly flat, then condition of complete interference is satisfied in a straight line across the surface as the surface at right-angles to the plane of the paper is parallel to the optical flat. • Therefore, a straight dark line will be seen passing through point C. Consider another ray incident along path SFH. • Again this ray is also slpitted into two components. It is obvious that the path difference of the two component rays will keep on increasing along the surface due to angle 9. • Thus if the path difference FHI be 3X12 or the next odd number of half wavelengths, then interference will occur and a similar fringe will be seen. • Next when path difference is 5K/2, again there will be another dark fringe. • At the intermediate point between the points C and H, the path difference will be an even number of half wavelengths and the two components will be in phase producing a light band. • Thus, in case of a perfectly flat surface, we will have pattern of alternate light and dark straight lines on the surface, as shown in Fig. 6.6. Any deviation from this pattern will be a measure of the error in the flatness of the surface being inspected.

N.P.L. Flatness Interferometer • This instrument, as the name suggests, is mainly used for checking the flatness of flat surfaces. • This interferometer was designed by National Physical Laboratory and is commercially manufactured by Hilger and Watts Ltd. • The flatness of any surface is judged by comparing with an optically flat surface which is generally the base plate of the instrument. • This instrument essentially consists of a mercury vapour lamp

• As we are interested in having single monochromatic source of light, the radiations of the mercury lamp are passed through a green filter. • The wavelength of the resulting monochromatic radiation is of the order or 0.0005 mm. • This radiation is then brought to focus on pinhole in order to obtain an intense point source of light. A mirror is used in order to deflect the light beam through 90°. • The pinhole is placed in the focal plane of a collimating lens, thus the radiations out of the lens will be parallel beam of light. • This beam is directed on the gauge to be tested via an optical flat. The fringes formed are viewed directly above by means of a thick glass plate semi-reflector set at 45° to the optical axis. • The gauge to be tested is wrung on the base plate whose surface is finished to a degree comparable to that of the highest quality gauge face. • As the optical flat is placed above it in a little tilted position, interference fringes are formed; one between rays reflected from the under surface of the optical flat and those reflected from the surface of the gauge, and the other between rays reflected from the under surface of the optical flat and those reflected from the base plate.

• If the gauge face is flat and parallel to the base plate, then the optical flat being equally inclined on both the surfaces the fringe pattern from both the gauge face and the base plate will consist of straight, parallel and equally spaced fringes as shown in Fig. a • When the gauge is flat but not parallel to the base plate, then straight and parallel fringes of different pitch above the gauge face as compared with those of the base plate are seen (Fig. b)

Surface of gauge is inclined to base plate. Gauge surface convex/concave. Slight rounding off at corners.

Leveling of the Machine • The level of the machine bed in longitudinal and transverse directions is generally tested by a sensitive spirit level. • The saddle is kept approximately in the centre of the bed support feet. • The spirit level is then placed at a-a (Fig. 16.1), the ensure the level in the longitudinal direction. It is then traversed along the length of bed and readings at various places noted down. • For test in transverse direction the level is placed on a bridge piece to span the front and rear guideways and then reading is noted • . It is preferable to take two readings in longitudinal and transverse directions simultaneously so that the effect of adjustments in one direction may also be observed in the other. • The readings in transverse direction reveal any twist or wind in the bed. It may be noted that the two guideways may be perfectly leveled in longitudinal direction, but might not be parallel to each other. This is revealed by the test in transverse direction. • The straightness of bed in longitudinal direction for the long beds can also be determined by other methods, e.g., using straight edges, autocollimators or by taut wire method. But the test in transverse direction can be carried out only by spirit level. • It is desired that the front guide way should be convex only as the cutting forces and the weight of carriage act downward on it. • If the front guide ways are concave, then the effect will be cumulative. • The tendency of the carriage, under cutting forces is to lift upwards from the rear and this is prevented by a gib placed underneath the guide ways. • With the result, an upward force acts on the rear guide ways ; which must, therefore, be made concave. • Transverse level may be in any direction, but no twist can be tolerated.

True Running of Lathe Main Spindle • Fig. shows the arrangement of test set up. • The test can be carried out by using a dial gauge and stand only. • Fix the dial gauge to stand and to a carriage of lathe machine. • Confirm that the plunger pointer touches the locating lathe spindle. • The headstock is then rotated on its axis and the indicator should not show any variation in reading.

Parallelism of Main Spindle to Saddle Movement • The dial gauge is to be mounted on the saddle and the feeler of dial should touch on the mandrel which is fixed in headstock of the lathe machine. • Move the saddle as shown in longitudinal direction and note the variation in dial gauge. • If no variation is present, they can be called as parallel to each other. Parallelism of Guide ways with the movement of carriage • Sometimes the job is held between headstock and tail stock centre for turning. In that case the job axis must coincide with the tailstock centre. • If the tailstock guide ways are not parallel with the carriage movement there will be some offset of the tailstock centre and this results in taper turning. • To check the parallelism of tailstock guide ways in both the planes i.e., horizontal and vertical, a block is placed on the guide ways as shown in Fig. and the feeler of the indicator is touched on the horizontal and vertical surfaces of the block. • The dial indicator is held in the carriage and carriage is moved. • Any error is indicted by the pointer of dial indicator. Alignment of Both Centers in Vertical Plane • A mandrel is fitted between the two centers and dial gauge on the carriage. • The feeler of the dial gauge is pressed against the mandrel in vertical plane as shown in Fig. and the carriage is moved and the error noted down.

Alignment Test on Milling Machine Cutter Spindle Axial Slip or Float • Axial slip is defined as the axial spindle movement which may repeat positively with each revolution . • When testing the axial slip of a spindle the feeler of the dial gauge rests on the face of the locating spindle shoulder and dial gauge holder is clamped to the table. • The locating spindle shoulder is rotated and change in reading is noted. • axial slip must always be tested at two points 180° apart on the collar of the spindle.

True Running of Internal Taper • The table is set in its main position longitudinally and the mandrel 300 mm long is fixed in the spindle taper. • A dial gauge is set on the machine table and feeler adjusted to touch the lower surface of the mandrel. • The mandrel is then turned and the dial readings at two points are noted i.e., one at the place nearest to spindle nose and other at about 300 mm from it. • For shifting the position of dial gauge from A to B cross-slide of the machine is operated to bring the dial gauge at the bottom of the end of mandrel. • There are can be two errors : (i) Axis of the spindle and the axis of taper may not be parallel. (ii) Eccentricity of the taper hole which, if present, should indicate same error at both the places. The error in first case will give different readings at two places. Due to this error, cut will not be shared equally between teeth of cutters, and therefore vibrations and poor finish will result.

Surface Parallel with Longitudinal Movement • For this test the dial gauge is fixed to the spindle. • Feeler is directed upon the surface the machine table and latter moved longitudinally. • The deviations from parallelism between the table surface and longitudinal motion are noted down. • If the table is uneven, a straight edge may be placed on the surface. • Due to this error the surface of the table will fluctuate up and down and cutter will not take equal cuts on the job which is clamped on the table and the milled surface will not be parallel to the base.

Traverse Movement Parallel with Spindle Axis (a) in horizontal plane; (b) in vertical plane. • The table is set in its mean position and dial gauge fixed on the table. • The table is moved crosswise and any deviation on reading of dial gauge is noted with feeler on one side of mandrel in horizontal plane and under the mandrel for error in vertical plane. • Due to this error, depth of cut will vary when cross slide is moved.

Alignment Test on Drilling machine

Flatness of clamping surface of base

• To perform this test, gauge block and straight edge are used. • Keep the gauge blocks on the base on which the straight edge is to be kept. • See the gap present between straight edge and base and check it by inserting slip gauges or feeler gauges. • The error should not exceed 0.1 mm per 1000 mm clamping surface. Perpendicularity of drill head guide to the base plate • The squareness (perpendicularity) of drill head guide to the base plate is tested : (a) in a vertical plane passing through the axes of both spindle and column, and (b) in a plane at 90° to the plane at (a). The test is performed by placing the frame level (with graduations from 0.03 to 0.05 mm/m) on guide column and base plate and the error is noted by noting the difference between the readings of the two levels. • This error should not exceed 0.25/1000 mm guide column for (a) and the guide column should be inclined at the upper end towards the front only, and 0.15/1000 mm for (b).

Parallelism of the spindle axis with its vertical movement • This test is performed into two planes (A) and (B) at right angles to each other. • The test mandrel is fitted in the tapered hole of the spindle and the dial indicator is fixed on the table with its feeler touching the mandrel. • The spindle is adjusted in the middle position of its travel. • The readings of the dial indicator are noted when the spindle is moved in upper and lower directions of the middle position with slow vertical feed mechanism.

True running of spindle taper • For this test, the test mandrel is placed in the tapered hole of spindle and a dial indicator is fixed on the table and its feeler made to scan the mandrel. • The spindle is rotated slowly and readings of indicator noted down. • The error should not exceed 0.03/100 mm for machines with taper up to Morse No. 2 and 0.04/300 mm for machines with taper larger than Morse No. 2.

Squareness of clamping surface of table to its axis • For performing this test, the dial indicator is mounted in the tapered hole of the spindle and its feeler is made to touch the surface of table (Refer Fig.). • Table is slowly rotated and the readings of dial gauge noted down, which should not exceed 0.05/300 mm diameter.

Squareness of spindle axis with table • For this test a straight edge is placed in positions AA’ and BB’. • Work table is arranged in the middle position of its vertical travel. • The dial indicator is mounted in the spindle tapered hole and its feeler made to touch the straight edge first say at A and reading noted down. • The spindle is rotated by 180° so that the feeler touches at point A’ and again reading is noted down. • The difference of two readings gives the error in squareness of spindle axis with table. • Similar readings are noted down by placing the straight edge in position BB’.

• Calculate the alignment error for the headstock and tailstock for the following data. • Initial reading of dial indicator = 0.1 mm • Final reading of dial indicator = 0.2 mm • Movement of carriage along longitudinal direction = 100 mm Solution -

H  0.2  0.1  0.1mm Alignmenterror is 0.1mm per100 mmof carriagemovement along horizontal axis of lathe H 0.1mm tan   L 100 mm   0.0572   003'26.26"