Patent GB-414865-A (GB)
Title: Method of and apparatus for compensating for play in machines for grinding or otherwise forming screw-threads
IPC: B24B19/02
Filed: 1933-05-17
Abstract: 414,865. Grinding &c. screw-threads. LINDNER, H., 9, Lubarser Strasse, Wittenau, Berlin. May 17, 1933, No. 14325. [Class 60.] In a machine for grinding or otherwise producing screwthreads particularly of the type in which the rotary workspindle 4 is moved axially past the tool under the control of a coaxial lead-screw 27, the backlash occurring on reversal of the work-spindle drive is compensated by means whereby the reversal of the work-spindle is always delayed by the maximum value of the backlash occurring in the lead-screw train and the axial reverse feed of the work-spindle which commences when the actual backlash has been taken up is rendered inoperative by opposite axial movement of the lead-screw so that the relative axial positions of the tool and work remain unaltered by the reversal. The work 3 is mounted between centres 1, 2, and is ground by a disc S. The work spindle is rotatably and slidably mounted in bearings 6, 7, in the headstock 5 and is driven from a pulley 9 through reversing bevel gearing 11, 13 and pulleys 14, 15, the latter being mounted on roller bearings on the work spindle and having a projection 19 engaging in a recess in a flange on the work spindle. This coupling has lost motion x corresponding to the maximum backlash. A toothed rim 17 on the pulley 15 drives the leading screw 27 through a long wheel 18 and change gears 22, 26. The leading screw engages in a nut 28 mounted in needle bearings in a cavity of the work spindle and slidably keyed in a casing 29 in the headstock. The leading screw may project into a cavity 4<11> of the work spindle and is mounted in a bearing sleeve 30 enclosed in a sleeve 31 serving as the inner ring of ball bearings, one of which 33, Fig. 5, has helical race grooves 31<1>, 32<1> of the same lead and preferably the same pitch as the lead-screw. The sleeve 31 has a projection 35 engaging with adjustable lost motion y, in a recess in the member 29, adjustment being effected by means of a screw abutment 36. In operation, when the rotation of the pulley 15 is reversed, the reversal of the work spindle is delayed while the maximum backlash x is taken up. When the actual lost motion, depending on the gears of the lead-screw train has been taken up, the leading screw starts its reverse rotation. This movement takes place not in the sleeve 30, but on the ball bearings 33, 34, and the helical race 31<1> causes the lead-screw to be moved axially in the direction of the arrow c. At the same time the coaction of the lead-screw with its nut moves the work spindle in the direction of arrow b. The movements band c being equal and opposite no axial movement of the work spindle takes place. When the maximum backlash x has been taken up, the projection 35 will have taken up the lost motion y and the lead-screw will then rotate in the bearing sleeve 30. When as is preferred, the pitch of the race 31<1> is equal to the lead-screw pitch, the lost motion y is equal to the difference between the maximum backlash x and the actual backlash. In modifications, the pitch of the race 311 may be greater or less than the lead-screw pitch, the lost motion y being then adjusted to compensate for the difference between the movements band c produced by the unequal pitches of the race 31<1> and the lead-screw. The tailstock spindle may move axially with the work against a spring 39 or a weight. For adjustment of the work relatively to the grinding wheel, a spindle 43 screwed into the headstock at 45 is rotated by a knob 44. The spindle engages a lever 46, one end of which passes through slots in the casing 29 and sleeve 32 so that, when the spindle is rotated the parts 29, 32, and the work spindle are moved axially. A spring 47 normally urges the casing 29 into contact with the lever 46.