From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Detailed description of a 3-Lap Recess Type Gear Lapping Machine's mechanisms, operation, and adjustments.
| Identifier | ExFiles\Box 155\3\ scan0008 | |
| Date | 23th October 1933 guessed | |
| The spindle carrying the work is positively driven through change gearing, and the three laps are rotated by the action of the work. A friction brake is applied to each of the three lap spindles, and the pressure can be varied to suit conditions. This pressure keeps the teeth of the laps in intimate contact with the work. The work-spindle can be adjusted endwise for position of work with relation to the laps, which are fixed as far as endwise motion is concerned. The laps, as previously mentioned, are held at a fixed center distance. The reason for this is that rigidity of lap and work-spindles is desirable if consistent results are to be obtained on a production basis. Since the work affords the only positive drive for each lap, and since the free rotation of each lap spindle is restrained by a friction brake, it is evident that each lap will be in positive contact with the work, thereby providing equalization of pressure and lapping action. The distribution of the lapping compound, and hence efficient lapping action, is facilitated by imparting a reciprocating movement to the work. The rotative drive is independent of the reciprocating mechanism, and the speed of either or both may be varied to suit conditions. The length of the reciprocating stroke may be varied from zero to one inch. In order to change the pitch line contact of each of the three laps on the work, each lap may be made with a different number of teeth. The center distances of the work-arbor and lap spindles are not adjustable, but through the medium of independent adjusting mechanisms the two upper lap spindles, which are mounted on self-aligning ball bearings, can be set at a slight angle with relation to the axis of the work. This feature makes possible the correction of slight errors in the axial relationship of the teeth resulting from heat treatment and will be found especially advantageous in lapping helical gears. Reversal of direction of rotation of work and laps, as well as the number of revolutions in each direction, is accomplished electrically through the medium of a reversing and limit switch. The limit switch can be set to any one of eight predetermined number of revolutions of the work, upon the completion of which the machine stops automatically. Operation of Gear Lapping Machine In operation, the work is clamped directly to the work-arbor, or is retained in a sleeve in the work-spindle, depending upon the design of the work. Fig. 2 shows a close view of the work and laps and also illustrates one type of support which is used when lapping shank or stem gears. Work-Reciprocating Mechanism The reciprocation of the work is effected by a crank motion, as shown in Fig. 3. The work-spindle is provided with cylindrical rack teeth and meshing with it is a segment gear which is connected to the rocker shaft. The endwise position of the work-spindle is adjusted by releasing the three screws E and rotating the rocker shaft by placing a wrench on stud F.{Mr Friese} An adjustment of 1 inch is possible through the elongated slots in crank arm connection G, and two positions are provided for the screws in the rocker shaft head, affording a maximum endwise adjustment of the work-spindle of 4½ inches. The length of stroke is effected through an adjustable crank-pin, as shown to the right in Fig. 3. Nut H is released and a wrench placed in screw I to adjust the crank-pin to the desired position. Provision is made for a maximum stroke length of 1 inch, but for gear work a maximum stroke of ⅜ inch is sufficient. The length of stroke used is governed to a large extent by the character and shape of the gear being lapped. On shoulder gears the amount of reciprocation is usually determined by the width of the recess. The rotative reciprocating speeds, as previously mentioned, can be varied through change gears, as shown in Fig. 4. Based on a motor speed of 1200 R.P.M., and a main drive shaft speed of 450 R.P.M., it is possible through change gears A and B to vary work-spindle speed from 50 to 300 R.P.M., as shown in Table I. The reciprocating speed of the work-spindle can also be varied, as shown in Fig. 4. Assuming the same motor and main drive speeds, as previously given, change gears C and D can be employed to obtain from 200 to 400 stroke cycles per minute, as indicated in Table II. Brakes for Lap Spindles In order to resist the free rotation of the laps by the work, and thus to facilitate the lapping action, each lap spindle is provided with an independent adjustable brake. This consists principally of a disk which is held in frictional contact with the driving disk by a series of compression springs. The compression of these springs, and hence the effective braking action, is adjusted as shown in Fig. 5 by a threaded nut J, which can be rotated when the locking pin K is withdrawn. To make this adjustment, the hand-hole plates on each side of the machine are removed, giving access to the brakes. The braking pressure is generally set at between 30 and 40 inch pounds at a radius of 4 inches. A simple way to make this adjustment is to place a wrench having a notch in the handle about 4 inches from the center of the head and to this, as shown in Fig. 6, attach a balance scale. The compression on the springs is increased until the balance scale pointer registers the desired amount when the frictional resistance of the brakes is overcome by pulling on the balance scale. Adjusting Axial Alignment of Lap Spindles Provision is made on this machine to change the axial alignment of the two upper lap spindles with relation to the axis of the work-spindle. This feature makes it possible to correct slight errors in axial position of gear teeth, and more especially the lead of helical gears caused by distortion in heat treatment. The two upper lap spindles are mounted on self-aligning ball bearings, and the rear bearing carriers are adjustable through hand-wheels located at the front of the machine. Dial indicators N reading to 1/10,000 of an inch, as shown in Fig. 7, are supplied to register the amount of axial adjustment. These indicators read directly the amount that the rear bearing is moved out of the axial position, the front bearing acting as a pivot. The central position is determined by a removable gage plate L which can be withdrawn by releasing the screw in clamping plate M when axial adjustment is necessary. The handwheels O and P, Fig. 1, are connected through gearing to the rear bearing carriers and are rotated to change the axial relationship of the upper lap spindles when the clamping plate is released, and the gage plate removed. In production, the lap spindles should be set in the axial position with gage plate L in place and clamped. FIG. 3. Close View Showing Crank Mechanism for Reciprocating, also Adjustment for Work Position and Stroke Length FIG. 4. Close View of Change Gears for Changing Work Revolutions and Reciprocating Speeds FIG. 5. Close View of Independent Adjustable Brakes on Lap Spindles, also Limit Switch for Controlling Number of Revolutions of Work in Both Directions FIG. 6. Illustrating Operator Testing Braking Pressure on Lap Spindles TABLE I Work-Spindle Speeds 3-Lap Recess Type Gear Lapping Machine (Speed of Main Drive Shaft 450 R.P.M.) R.P.M. of Work-Spindle | Number of Teeth in Change Gears A | B 50 | 20 | 60 75 | 27 | 53 100 | 32 | 48 125 | 36 | 44 150 | 40 | 40 175 | 43 | 37 200 | 46 | 34 225 | 48 | 32 250 | 50 | 30 275 | 52 | 28 300 | 53 | 27 TABLE II Work-Spindle Reciprocations 3-Lap Recess Type Gear Lapping Machine (Speed of Main Drive Shaft 450 R.P.M.) Stroke Cycles of Work Per Minute | Number of Teeth in Change Gears C | D 200 | 20 | 44 220 | 21 | 43 235 | 22 | 42 250 | 23 | 41 270 | 24 | 40 290 | 25 | 39 310 | 26 | 38 330 | 27 | 37 350 | 28 | 36 370 | 29 | 35 400 | 30 | 34 | ||