Volume 16 - Machining Part 17 pptx

Prepared proprietary oils that contain buffers are widely used. Before use, these oils (which may also contain rust inhibitors and deodorants) are diluted up to 95% with kerosine. The use of too much buffer may detract from its beneficial effects. An excessive amount: • Reduces the cutting action of the abrasive • Produces smoother finishes • Requires higher pressures or lower rotational speeds • Lowers the ability of the fluid to dissipate heat • Impairs fluid distribution • Increases requirements for refrigeration and filtering Regardless of the type of fluid used, it should be delivered to the honing stones in a constant and generous supply. The fluid also should be filtered through a system that removes particles coarser than 15 m (600 in.). The system should be kept free of water and stray oil (such as from the hydraulic system), which adversely affect the properties of honing fluids. In many plants, 17 to 20 °C (62 to 68 °F) is the preferred temperature range for honing fluids. Controlling the temperature becomes more important as tolerances become closer. If temperature is allowed to rise, dimensions may become inaccurate and the fluid may break down, causing excessive stone wear and changes in cutting characteristics. In production installations, heat exchangers are often used to maintain close control of honing fluid temperature. Dimensional Accuracy Internal honing to tolerances of 0.025 to 0.0025 mm (0.001 to 0.0001 in.) is common. For some high-precision parts, tolerances as close as a few millionths of an inch are specified and achieved. Close tolerances can be produced and repeated in fixtured honing (power stroking) if sources of variation, such as machine and honing fluid condition, are closely controlled, as described in the example below. Example 1: Variations in Dimensions and Finish for 900 Cylinder Blocks. The data plotted in Fig. 19 represent results of a quality control check made on 99.31 mm (3.910 in.) diam cylinder bores in gray iron blocks for V-8 engines. Bores 2 and 7 were measured in 11 blocks from a production run of 900. The conditions employed in honing these bores are presented in Table 10. Table 10 Processing details for honing cylinder bores in V-8 engine blocks Processing details (a) Machine production rate 70 blocks/h Spindle speed 204 rev/min Spindle reciprocation 78 strokes/min Stock removal: Amount 0.051-0.102 mm (0.002-0.004 in.) Time 39 s Honing fluid Mineral seal oil (b) Stone life per set (c) 450 blocks Size control Spindle-mounted plug gage Dimensional tolerance Max out-of-roundness and taper, 0.025 mm (0.001 in.) Finish 0.50-0.89 m (20-35 in.) Crosshatch angle 22 ° (a) Bores are cl assified in five sizes differing 0.013 mm (0.0005 in.) in diameter, for selective fitting of pistons. (b) At 20 °C (68 °F), heat exchanger is required for maintaining this temperature, and honing fluid must be free of water and tramp hydraulic oil. (c) Silicon carbide stones Fig. 19 (a) Surface finish, (b) taper, and (c) out-of-roundness variations obtained in honing. Data r epresent measurements on cylinder bores 2 and 7 in 11 gray iron blocks for V- 8 engines, selected from a run of 900. Measurements were made on blocks 1, 50, 100, 200, 300, 400, 500, 600, 700, 800, and 900. The honing fluid was maintained at 20 °C (68 °F) by the use of a heat exchanger, and was constantly filtered. Less than 2% of the 7200 bores honed required a repair operation because either taper or out-of-roundness exceeded the specified 0.025 mm (0.001 in.). Surface Finish Surface finish of 0.25 to 0.38 m (10 to 15 in.) can be obtained easily in production honing, and finish of less than 0.050 m (2 in.) can be achieved and reproduced. A range of roughness is sometimes specified. In other applications, a maximum surface roughness is specified. Under carefully controlled conditions, surface roughness can be maintained within a close range, as indicated in Fig. 19. Size of grit in the honing stones is the main factor controlling surface finish. When grit is fine, the finish will be fine (other factors being equal); but as grit size is decreased, rate of stock removal is also decreased, as described in the following example. Example 2: Honing Gray Iron to a Finish of 0.25 to 0.38 m (10 to 15 in.). In honing gray iron (hardness, 170 to 195 HB), a finish of 0.25 to 0.38 m (10 to 15 in.) was desired. Silicon carbide stones with a grit size of 180 produced a roughness of 0.63 to 0.75 m (25 to 30 in.). The required finish could be obtained with 320-grit stones, but the time required for honing made the use of this grit size impractical. The problem was solved by first rough honing with 180-grit stones and then finish honing, in another setup, with 320-grit stones. Rough finishes are sometimes improved by using a dwell time at the end of the honing cycle that is, by continuing the rotation and reciprocation action for a few strokes after feed-out ceases and pressure drops off. In manual honing of a particular bore, use of this technique reduced surface roughness from the normal 0.50 to 0.25 m (20 to 10 in.). Honing Practice for Internal Diameters Honing is widely used for finishing bores in engine cylinders, cylinder liners, and bearing bores. Procedures for honing similar parts may vary from one plant to another, depending on quantity, available equipment, and established plant practice. As a rule, honing stones and techniques used for honing cast iron are different from those used for aluminum alloys. However, there are exceptions as in the case of an assembly of cast iron and aluminum in which the two metals were honed simultaneously, with the same abrasive, because it was the simplest way to achieve a proper fit. Small Bores. Conventional manual-stroking honing tools (Fig. 9) are available for use in bores as small as 1.6 mm ( in.) in diameter in parts such as fuel nozzles, miniature bearings, and heading dies, as in the following example. Example 3: Honing Very Small Bores. Dies for cold heading tiny rivets and screw blanks had bores as small as 1.6 mm ( in.) in diameter. Bore length varied, but was usually 25 to 50 mm (1 to 2 in.). Figure 20 shows one of the heading dies, which was made of tool steel, and a typical product of the die. Holes were drilled and reamed about 0.075 to 0.13 mm (0.003 to 0.005 in.) undersize before heat treatment. After hardening, they were honed, using manual stroking, to an accuracy of 0.0025 mm (0.0001 in.) for both roundness and straightness. Fig. 20 Bore of die for cold heading the rivet shown at the left is typical of small bores finished by manual- stroke honing. Dimensions given in inches Large Bores. The maximum diameter and length of bore that can be honed is limited mainly by the size of the equipment required for the workpiece and by the power required for the tools. Equipment with drive motors of up to 37 kW (50 hp) is available for honing steel shells of 1040 mm (41 in.) inside diameter (ID) and 19 m (63 ft) length. Cylinder shells for hydraulic hoists on regulating gates for dams are examples of large bores that are honed. In one honing operation, 0.75 mm (0.030 in.) of stock is removed from a 6.4 Mg (14,000 lb) shell of 760 mm (30 in.) ID and 7.9 m (26 ft) length to obtain a total envelope tolerance of 0.050 mm (0.002 in.). Before honing, the average out-of-roundness is 0.41 mm (0.016 in.). Short Bores. Several different techniques are used for honing short bores. These are particularly applicable when bore diameter exceeds length. In the simplest method, several pieces are stacked with bores aligned, clamped tightly by any suitable means, and honed as a unit. For example, 13 mm ( in.) long rings 38 mm (1 in.) in inside diameter can be honed in stacks of eight. In effect, this would be the same as honing a single piece 100 mm (4 in.) long. Stacked parts may be either manually or power stroked. However, for successful results from this technique, the parts must have parallel sides to permit building a straight stack that can be clamped tightly and provide a straight bore. Another technique that has proved successful for honing short bores is shown in the following example involving automotive-engine connecting rods (compare with newer method shown in Fig. 15). Example 4: Short-Bore Honing Technique for Connecting Rods. A power-stroking horizontal machine was used in high production for honing 61.54 mm (2.423 in.) ID crankpin bores simultaneously in eight connecting rods. Figure 21 shows the fixture and the honing tool. Eight rods were stacked between 4.8 mm ( in.) wide parallel separator plates, resulting in an effective bore length of 260 mm (10 in.). The tool had three banks of four honing stones. Each stone was 9.5 mm ( in.) square and 57 mm (2 in.) long. A two- station, rotary index table allowed the operator to unload eight completed rods and to load eight unfinished rods while eight other rods were being honed. A precheck plug probed the rods in the loading station to determine whether they had been bored to proper rough size. The operation completed one bank of rods in 45 s, floor-to-floor time, and a production rate of about 600 rods/h was obtained. In honing, 0.075 mm (0.003 in.) of stock was removed, a finish of 0.75 to 1.14 m (30 to 45 in.) was produced, and inside diameter was controlled within 0.13 mm (0.0005 in.). Fig. 21 High- production honing of automotive parts. Fixture designed to hone crankpin bores on eight automobile connecting rods simultaneo usly, using a single honing tool. Rotating fixture permitted loading and unloading on one side while parts on the opposite side were honed. Blind holes are bores that have a bottom, shoulder, or other obstruction that prevents a tool from passing completely through. The three most common types of blind holes are shown in Fig. 22. Most unrelieved blind holes can be honed satisfactorily, but there will always be some unfinished area at the bottom. The amount depends on length of bore, type of material, tolerance required, and amount of stock removed. Under the best conditions, dead-blind holes can be honed to within about 0.38 mm (0.015 in.) of the end. Any relief will improve results; as much relief as possible is preferred. Sometimes an unrelieved blind hole is in effect provided with a relief because specified tolerance and finish need not be met at the bottom of the hole. Fig. 22 Three types of blind holes Special tools may be required, depending on whether or not relief (or on how much relief) is provided. For example, the unrelieved 13 mm ( in.) diam bore shown in Fig. 23(a) was manual-stroke honed to within about 0.38 mm (0.015 in.) of the end with a special tool having a hard-tipped honing stone (Fig. 11c). If adequate relief is provided, conventional tools are satisfactory. For example, cylinder heads in lawn mower engines (Fig. 23b) can be manual-stroke honed in high production with conventional tools, because of the generous relief (about 6.4 mm, or in., wide) at the blind end. Although both parts shown in Fig. 23 were manual-stroke honed, similar parts are frequently honed by power stroking. Fig. 23 Blind holes honed by different methods. (a) Unrelieved blind hole that required a special tool (see Fig. 11c) for honing. ( b) Relief that permitted use of a conventional honing tool in the bore of a cylinder head for a lawn mower engine. Dimensions given in inches Delivering enough honing fluid to the work area is often a problem in honing blind holes. When a hole has a bottom opening (Fig. 23b), fluid can be pumped through a plastic tube inserted in the opening. When a hole has no bottom opening, the flow of fluid should be directed parallel to the mandrel, into the mouth of the bore. In manual honing, blind holes are more difficult to keep straight than open holes. A truing sleeve (dummy workpiece) is frequently used to keep the shoes and stones straight and parallel; also, the stone and shoe are made shorter than the blind hole. Experienced operators have found that using a series of short strokes with an occasional stroke all the way out of the mouth is the best practice, until the hole is close to final diameter. This keeps the bottom slightly larger than the mouth. Straight strokes are then used for finish honing. Tapered Bores. Part size, angle of taper, and length-to-diameter ratio determine the method used in taper honing. Short tapers are honed using a machine and tool such as that shown in Fig. 24. The machine has a head that can be positioned for any desired degree of taper, and the reciprocating tool holds a single stone. The workpiece is rigidly clamped in a fixture that rotates. This method is most commonly used for producing tapers on parts for which the length of honed area is less than the diameter. As the length of the taper increases in proportion to the diameter, however, the practicality of the method decreases, because the longer and more slender tools lack adequate rigidity. Fig. 24 Machine and tooling for honing short, tapered bores Applications of this method of taper honing include special bearing rings and parts that use end tapers for sealing, and bores in gears that must fit tapered shafts. For example, drum-to-barrel seals in a 20 mm gun must have a taper of 0.050 mm/mm (0.050 in./in.) of length at each end and roughness less than 0.25 m (10 in.). To meet these requirements, 0.01 to 0.05 mm (0.0005 to 0.002 in.) of stock must be removed from the critical surfaces. Taper honing long bores in large parts is far more complex than honing short tapers. A major portion of the stock is removed by step honing. In this operation, a straight stroke is used, its length being progressively reduced to form a rough taper consisting of a series of small steps. The taper is then finished in a second operation in which a sine bar regulates the increase and decrease of the diameter on the return and forward stroke of the honing cone. Special Shapes. Machines and tools have been developed for honing various special shapes. For female splines, honing stones must be narrower than the spline width (preferably no wider than half the spline width) to allow for oscillation. Machines and tools for honing splines are designed to produce simultaneous reciprocation and oscillation, rather than reciprocation and rotation. Relief bores are commonly honed by contour boring. Special Applications of Honing A few special uses of honing should be enumerated as a means of indicating the potential of the honing method beyond the field of its basic and most extensively accepted applications. These are related to the honing of internal cylindrical surfaces by using regular abrasives for obtaining specific dimensional conditions of the work surface. Among these related processes are: • External honing • Gear tooth honing • Plateau honing • Flat honing • Electrochemical honing • Hone forming External Honing. Honing has been used to only a limited extent for finishing outside diameters, largely because required dimensions and finish can be produced at less expense by other processes, such as centerless grinding. However, advances in metrology and improved honing techniques have resulted in an increase in the number and scope of applications of external honing. Special machines and special adaptations of conventional machines (such as lathes) have been tooled to hone outside surfaces of metal parts. With these machines, either power or manual stroking may be employed. Fixtured external honing (power stroking) is widely used for pieces that are not adaptable to competitive methods. A notable example is the finishing of grooves in bearing races. Special machines that simultaneously rotate the workpiece and oscillate the stones (Fig. 25) produce the crosshatch lay pattern characteristic of a honed surface. Fig. 25 Fixtured honing of grooves on external surface of bearing rings with simultaneous oscillation of honing stone and rotation of workpiece Manual external honing is applicable to the removal of small amounts of stock from external diameters of a wide variety of sizes and shapes. The honing of lengths up to 3 m (10 ft) is common practice. Conventional honing machines are generally used for rotating workpieces up to 610 mm (24 in.) long. Lathes or drill presses are preferred for longer workpieces. Tools such as that illustrated in Fig. 26 are available for honing parts ranging in outside diameter from about 3.05 to 69.85 mm (0.120 to 2.750 in.). With this setup, the sides of the tool are gripped and stroked over the rotating workpiece. Feed- out and cutting rate are controlled by applying pressure to the honing-control lever, which will move through a preset distance. Size is controlled automatically by setting the micrometer stone feed-out so that the honing-control lever will be against the stop pin when the correct size is attained. The only adjustment needed during the honing operation, even in production runs, is a slight additional stone feed-out to compensate for stone wear. A turn of the honing-control lever will instantly disengage the stone from the work for quick gaging or unloading, but will not change the setting on the micrometer stone feed-out. Fig. 26 Assembly used for manual-stroke honing of outside diameters. See text for discussion. With the setup shown in Fig. 26, a line of stones with opposing guide shoes, or opposing stones, can be used. For honing long parts (up to 610 mm, or 24 in.), multiple holders that contain as many as three stones (or shoes) in line may be used for correcting waviness. The torque arm can be used to offset the tendency of the tool to turn. A guide bar mounted on the machine acts as a stop for the torque arm. This type of tool can produce dimensional accuracy to 0.0025 mm (0.0001 in.) or better and surface roughness as low as 0.050 m (2 in.). Manual-stroke external honing has replaced lapping in some applications, because: • Honing is usually faster • Soft metals can be honed without being impregnated with abrasive • The use, in honing, of multiple-length stones and shoes allows better control of bow and waviness Long anodized aluminum tubes for in-flight refueling are honed externally in a lathe, the honing tool being moved by hand, and the nozzle for the honing fluid moving with the tool. Crankpins of some crankshaft are honed the same way at overhaul. Gear-tooth honing is an abrasive process designed to improve geometric accuracy and surface conditions of a hardened gear. The teeth of hardened gears are honed to remove nicks and burrs, to improve finish, and to make minor corrections in tooth shape. Gear teeth are honed on high-speed machines specially designed for the process (Fig. 27). The honing tool is like a gear driving the workpiece at high speed (up to 30 m/min, or 100 sfm) while oscillating so that the teeth slide axially against the workpiece. Fig. 27 Honing teeth of helical gears Spur gears and internal or external helical gears ranging in diametral pitch from 24 to 2.5, in outside diameter from 19 to 673 mm ( to 26 in.), and up to 75 mm (3 in.) in face width have been honed on these machines. Finishes of 0.75 m (30 in.) are easily achieved, and finishes of 0.075 to 0.10 m (3 to 4 in.) are possible. Both taper and crown honing can be done. Tools used in honing gear teeth are of two types, a helical gear shape tool made of abrasive impregnated plastic, and a metal helical gear with a bonded abrasive coating that is renewable. The plastic tool, which is discarded at the end of its useful life, is widely used. The metal tool is used mainly for applications in which plastic tools would be likely to break; also, it is used primarily for fine-pitch gears. Plastic tools are supplied with abrasives of 60-grit to 500-grit size. Size of abrasive, gear pitch, and desired finish are usually related as: Finish Grit size Gear pitch m in. 60 16 0.75-0.89 30-35 100 16-20 0.63-0.75 25-30 180 >20 0.38-0.50 15-20 280 >20 0.25-0.30 10-12 500 >20 0.075-0.10 3-4 Honing tools do not load up, and a plastic honing tool can wear until its teeth break. Stock removal of 0.025 to 0.050 mm (0.001 to 0.002 in.) measured over pins is the recommended maximum. Methods. The two methods used to hone gear teeth are the zero-backlash method and the constant-pressure method. In the zero-backlash method, which is used for gears made to commercial tolerances, the tool head is locked so that the distance between the center of the work gear and the center of the honing tool is fixed throughout the honing cycle. In the constant-pressure method, which is used for gears produced to dimensions outside commercial tolerance ranges, the tool and the work gear are kept in pressure-controlled tight mesh. Applicability. The use of honing for removing nicks and burrs from hardened gears can result in a considerable cost saving in comparison to the usual method. In the usual method, the gears are tested against master specimens on sound test machines. Nicks indicated are searched for and removed using a hand grinder. The gear is then retested to make certain the nick has been removed. When honing is used, all of these various tests and procedures can be eliminated. Some shape correction can be achieved in the removal of 0.050 mm (0.002 in.) of stock by honing. A helical gear 127 mm (5 in.) in diameter may show lead correction of 0.010 mm (0.0004 in.), involute profile correction of 0.0075 mm (0.0003 in.), and eccentricity correction of 0.010 mm (0.0004 in.). The advisability of using honing for salvaging hardened gears hinges on cost considerations. As the error in tooth shape increases, honing time increases and tool life decreases. On the other hand, if the gears represent a large investment in production time and material, honing may be the most economical method. Because honing is not designed for heavy stock removal or tooth correction, it cannot be substituted for grinding or shaving of gears. Rotary shaving usually leaves gear teeth smooth within 0.25 to 1.00 m (10 to 40 in.). Plateau honing produces a special plateau finish, which removes the surface peaks but retains the deep valleys. Such a finish has been found desirable in engine performance because the valleys act as oil reservoirs for improved lubrication, especially during engine break-in. A plateau finish is produced by first rough honing to final size. Then the surface is finished with a finer-grit stone for about 45 s, depending upon the amount of plateauing desired. The plateauing operation, with a 600-grit stone, removes so little stock that the bore diameter is not measurably increased. Flat honing is a term designating a method and the equipment by which the flat surfaces of component parts produced by other methods are improved with regard to both flatness and parallelism of opposite surfaces. One of these surfaces may be that on which the part is located during the honing of the opposite face, or both faces may be honed simultaneously on machines operating with two honing disks. The equipment used is similar in appearance to rotary face-grinding machines, but it is adapted to honing, a method which differs from grinding particularly in the low cutting speed of the abrasive disk, the applied speed being comparable to that used in conventional honing. The bonded abrasive disks used in flat honing are generally not intended for substantial rates of stock removal and thus can have very fine grains, promoting the development of a high-grade finish, even of the order of 0.025 m (1.0 in.) R a when needed. The spindle of the honing disk used on flat honing machines can be raised and lowered by an air or hydraulic cylinder. Single- or double-surface flat honing machines are designed for high-production uses, finishing typically 1200 to 1800 parts per hour in a fully automated operation controlled by a timer. On two-wheel machines (see Fig. 28), the top wheel, lower wheel, and workholder each have separate drives and controls. Machines are available with automatic controls to gradually increase pressure on the top wheel during the honing cycle. Automatic size control is also available. The workpiece carrier is part of an epicyclic sprocket holder. [...]... 0.763 0-4 0 1.00 0.763 0-4 0 1.00 0.381 5-2 5 0.63 0.763 0-4 0 1.00 2.5 0-5 .0 100200 5. 0-6 .3 200250 0.251 0-2 0 0.50 0.381 5-2 5 0.63 0.251 0-2 0 0.50 1.004 0-5 0 1.25 Number of spindles on microhoning machine Surface configuration Spherical or flat Finish after microhoning m 0.12 5-0 .20 1 Production rate, parts/h in 5-8 900 10 Cylindrical 0.12 5-0 .20 5-8 80 2 Cylindrical 0.05 0-0 .10 2-4 120 12 Cylindrical 0.07 5-0 .125 3-5 ... various sizes of ring gages Diameter mm 0.73 7-2 0.96 20.9 6-3 8.35 38.3 5-6 3.75 63.7 5-1 14.55 114.55 -1 65 .35 165 .3 5-2 28.85 in 0.02 9-0 .825 0.82 5-1 .510 1.51 0-2 .510 2.51 0-4 .510 4.51 0-6 .510 6.51 0-9 .010 Tolerance for gages of class: X Y mm in mm 0.0010 0.000040 0.0018 0.0015 0.000060 0.0023 0.0020 0.000080 0.0030 0.0025 0.000100 0.0038 0.0033 0.000130 0.0048 0.0040 0.00 0160 0.0061 in 0.000070 0.000090 0.000120 0.000150... 10 Cylindrical 0.12 5-0 .20 5-8 80 2 Cylindrical 0.05 0-0 .10 2-4 120 12 Cylindrical 0.07 5-0 .125 3-5 720 2 Flat 0.1 8-0 .30 7-1 2 100 1 Internal cylindrical 0.3 8-0 .63 1 5-2 5 150 12 Cylindrical 0.05 0-0 .10 2-4 800 10 Cylindrical 0.05 0-0 .10 2-4 80 9 Flat 0.05 0-0 .10 2-4 500 2 Cylindrical 0.05 0-0 .10 2-4 450 Starting finishes for pressure plates and brake drums are for turned surfaces rather than ground In some... Alumina 2-1 0 m (8 0-4 00 in.) Medium hard 900 Alumina 5, 10, 15 m (200, 400, 600 1-3 m (4 0-1 20 in.) Soft Alumina 1, 2 m (4 0-8 0 in.) Hard and sharp 600, 800, 1000 Silicon carbide Medium soft 600, 800 Garnet 10 m (400 in.) Medium soft 800 Emery Chromium oxide Medium soft 1 m (40 in.) Soft Ferric oxide 1 m (40 in.) Medium hard Cerium oxide 1, 2 m (40, 80 in.) Typical applications Tool-room lapping Tool-room... abrasive so that the grit particles act on the opposing surfaces Irregularities that prevent the surfaces from fitting together precisely are thus eliminated, and the surfaces are mated In many cases, a part is first lapped individually and is then mated with another part by this method, before the two are stocked as a pair of lapped-together parts Matched-piece lapping enables mating parts (such as the heads... accurate parts Taper can be minimized by positioning the workholder so that the parts in the slots are at a 15° angle to a radius, as illustrated in Fig 5 Fig 5 Setup for lapping production quantities of the valve needle shown in Fig 3 Because machine lapping between plates uses diametrically opposed laps, it cannot correct the out-of-roundness produced by centerless grinding However, out-of-roundness... Centerless lapping is a high-production operation that is particularly suited to centerless ground parts that can be continuously fed, either manually or automatically Parts 6 to 150 mm ( to 6 in.) in diameter by 380 mm (15 in.) long can be centerless lapped, and when a long bar feed is used, it is possible to lap parts 13 to 75 mm ( to 3 in.) in diameter and 4.6 m (15 ft) long Typical parts finished by centerless... formulations; this provides a good-quality suspension, good film-forming properties (and therefore good lubricity), and a water-soluble mixture that is readily cleanable Clay or mica is occasionally mixed in to fill the voids between the abrasive particles, thus enhancing the suspension Ionic, charged, and submicron particles are also used as suspension agents These particles affix themselves to the... bonded-abrasive laps must be dressed with diamond tools, it is not possible to make them as flat as cast iron laps, on which the machines regenerate flatness The quantity of parts being lapped is less critical for machines using bonded-abrasive laps than for machines using cast iron laps, because both bonded-abrasive laps are rigidly supported on spindles and separately driven As few as three parts... Parts with shoulders require special workholders that permit the shoulder section to be placed on the inside or outside of the lap face Parts with keyways, flats, or interrupted surfaces are difficult to lap by machine, because the variations in pressure that occur are likely to cause out-of-roundness If the relief extends over the entire length of the piece, this method of lapping cannot be used Parts . Gear pitch m in. 60 16 0.7 5-0 .89 3 0-3 5 100 1 6- 20 0.6 3-0 .75 2 5-3 0 180 >20 0.3 8-0 .50 1 5-2 0 280 >20 0.2 5-0 .30 1 0-1 2 500 >20 0.07 5-0 .10 3-4 Honing tools do not. 0.05 0-0 .10 2-4 120 Distributor shaft 0.7 6- 1.00 3 0-4 0 12 Cylindrical 0.07 5-0 .125 3-5 720 Pressure plate (a) 2.5 0-5 .0 10 0- 200 2 Flat 0.1 8-0 .30 7-1 2 100 Brake drum (a) 5. 0-6 .3 20 0- 250. rate, parts/h Tappet head 0.7 6- 1.00 3 0-4 0 1 Spherical or flat 0.12 5-0 .20 5-8 900 Crankshaft 0.7 6- 1.00 3 0-4 0 10 Cylindrical 0.12 5-0 .20 5-8 80 Stem pinion bearing 0.3 8- 0.63 1 5-2 5 2