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).
Reprint from American Machinist detailing the Bethlehem Torque Amplifier and Lashlock systems for eliminating backlash.
| Identifier | ExFiles\Box 154\3\ scan0060 | |
| Date | 4th November 1927 guessed | |
| depart far from the wedge and roller already illustrated, but all in fact adhering to the essentials of positive locking and automatic release of friction. One such alternative construction is the double cam shown in Fig. 4. Here a double cam replaces the wedge, with faces A4; the stem, B, is a pivot on which the cam revolves. Pressure of either one of the rollers C and D will cause a frictional locking between cam and pivot, because the cam faces are cut on an involute so that the pressure of the rollers is always a little to one side of the center. Pressure of both rollers simultaneously relieves the friction between cam and pivot and rotates the cam. The spring, E, urges the cam in a rotary direction opposite to that caused by pressure of the rollers. This form of lashlock is interchangeable with the straight-side wedge, but fits better into certain constructions. Another form of lashlock is that shown in Fig. 5. Here the place of the wedge member is taken by a member, A, of the shape shown. This is provided with two lugs, B and C, and with two downwardly-projecting arms which form a partial cap embracing the member D, corresponding to the stem of Fig. 1. Members A and D are threaded into each other. No rollers are necessary. Simultaneous pressure on opposite sides of lugs B and C, as indicated by the arrows, rotates member A on member D; but pressure on only one lug produces a cooking effect, causes a frictional lock and prevents rotation. All the pressure on the one lug therefore acts to move the stem in the direction in which the lug delivers the pressure. This cooking and binding effect is the same thing that occurs when one attempts to open a bureau drawer by pulling on one handle; pressure on both lugs corresponds to pulling both handles together. This form of lashlock is used in the torque amplifier, or in any type of mechanism operating through friction bands, where it is desirable to eliminate backlash when reversal occurs between one drum and its oppositely rotating mate. It has not the high degree of accuracy of other' forms. As to the accuracy of the lashlock, while backlash elimination between moving members, by positive means, cannot be theoretically absolute, this theoretical play is insignificant with the lashlock. Severe tests have been made to determine this point. For example, a train of worms and gears (all stock parts) was arranged to give a reduction of 200 to 1 and the angular movement of the primary drive gear and that of the final driven gear measured during a reversal of direction. The backlash of the driven gear was found to be less than 1/10 part of a minute of arc, which is negligible. Gearing in this test was fairly heavy, designed to transmit 30 lb.-ft. of torque. Similar tests were made on a screw-feed, the screw used being one removed from the cross-feed of a lathe because of excessive wear. A carriage was mounted on this screw and its cross movement measured during reversal of direction of the feed-handle. Backlash was found to be well within one ten-thousandth of an inch of carriage travel. Initial accuracy of gear teeth and screw threads is not, of course, bettered by the lashlock although, because of the double drive, inaccuracies are halved, or at least averaged. The lashlock can be applied to gears, screws, bearings, thrusts, linkage motions, sliding parts and frictionally driven parts, as shown in Figs. 6-9. In some machinery the space required for its installation may prove an obstacle; because of its adaptability, however, and the variety of forms which it can assume, it is usually easy to incorporate it in a design. The lashlock is applicable to two general classes of machinery: those in which great accuracy is the chief factor, such as certain machine tools, precision instruments and fire control apparatus: and machines where the elimination of backlash will result in the production of better work and in prolonging the life of the machine by reducing the wear arising from looseness and chatter. [ 8 ] [Title Page] The Bethlehem Torque Amplifier and The Bethlehem Lashlock (An automatic backlash eliminator) Reprinted from AMERICAN MACHINIST Research and Development Department Bethlehem Steel Company Bethlehem, Pa.{Mr Paterson} | ||