Patent GB-406920-A (GB)
Title: Feed mechanism for metal cutting machines
IPC: B23F5/16
Filed: 1933-07-24
Abstract: 406,920. Gear cutting. SYKES, W. E., 33, Gates Circle, Buffalo, New York, U.S.A. July 24, 1933, No. 20828. Convention date, July 22,1932. [Class 83 (iii).] A feed mechanism, particularly for a gear-cutting machine operating as described in Specification 169,891, [Class 83 (iii)], comprises a feed element which is moved by an actuating device to successive advance positions, the feed element being adjustable to vary the total advance thereof, and the actuating device being adjustable to divide the total movement into variable successive step movements and to determine the relative dimensions of said step movements. The gear blank b is cut by two reciprocating pinion cutters a which have a twisting motion for shaping helical teeth and are rotated in timed relation with the blank to generate teeth over the whole periphery of the blank. The twisting movement of the cutters may be dispensed with for cutting straight teeth. The work-spindle is rotated by worm gearing from a shaft 24. In order to feed the cutters to the desired depth the gear blank spindle is mounted on a carriage 21 which is slidable towards the cutters on guides 23 and is actuated by a feed screw 27 operable, for hand feeding, from a hand wheel 29. For automatic feed the feed screw is enclosed by a sleeve 30, Fig. 5, confined between thrust bearings and held against rotation. The sleeve is threaded externally to engage a nut which is formed as a gear-wheel 39 and is rotated by a rack 45 to impart bodily axial movement to the sleeve 30 and feed screw. To prevent rotation of the feed screw when this automatic feed is employed a rod 42 having a wedge shaped end is moved axially by a hand wheel 40, thus moving radial members 43 outwards into engagement with the fixed sleeve 30. The rack bar 45 has periodical feed movements of variable length towards the right, Fig. 7, these movements being effected by a star wheel device having a number of studs 51 which are adjustable along slotted arms 52, the adjustment being indicated by means of scales 56. As the star wheel rotates the studs engage successively with a lug 57 secured to the rack-bar to impart a step-by-step feed thereto. In addition to the studs, the star wheel is provided with a preferably fixed rim 58 whose forward face 59 produces a very small finishing feed after which the concentric portion 58 maintains the rack bar in a fixed position until the part 58 passes off the lug 57 whereupon the rack bar is returned by springs 61 to a starting position wherein the bar engages a stop 63 adjustable in a movable block 65. In the withdrawn position of the rack bar the block 65 is pressed against a fixed abutment block 67 through which the screw stop may slide. During operation the rack bar is held against return movement by a tooth 72 on a pivoted lever 70 and also by a roller 73 which is jammed between an inclined guide 74 and the rack bar by means of a spring-pressed member 77. Both these devices permit the intermittent feed to the right but prevent return movement until the nose of the segment 58 engages a pin 79 on the lever 70 to disengage the tooth 72 from the rack bar and push back the roller 73. Thus after the segment 58 leaves the lug 57 the rack bar is returned by the springs 61. The star wheel is actuated either manually or automatically. For this purpose a helical gear on the work spindle drives a gear 83, Fig. 13, loosely mounted on a shaft 84 and coacting with a loose coupling sleeve 91 having a sliding connection 93 with a bevel gear 95 fast on the shaft 84. This shaft is connected through gears 86, shaft 88, and other gearing to the shaft 110 on which the star wheel is mounted. For manual operation the coupling sleeve 91 is disengaged from the gear 83 by lever mechanism actuated from a handle 98 and the shaft 84 rotated through the bevel gearing 95 from a hand wheel 102 on shaft 103. For the automatic feed the coupling sleeve is positioned as shown in Fig. 13. When the rack bar is returned at the end of the operation, the block 65 carrying the gauge is forced back against an abutment 67 and this movement is utilised to actuate a control 113 for stopping the motor driving the machine. In operation the feed screw is first turned by hand until the cutters just engage the work and the star wheel is rotated by the hand gearing to set the rack bar to that starting position necessary to give the desired depth of cut (indicated by a scale 115). The return stop is then adjusted up to the rack in this position and the studs of the star wheel adjusted to divide the depth feed into the desired number of steps each of any fractional part of the total depth. The feed screw is then locked to the sleeve 30 and the machine started. The gearing is arranged so that the blank makes rather more than one revolution for each step of the feed.