Patent GB-546170-A (GB)
Title: Improvements in the manufacture of threaded machine parts
IPC: B23G1/02
Filed: 1940-09-09
Abstract: 546,170. Lathes. CHESHIRE, G. S. Sept. 9, 1940, No. 12766. [Class 83 (iii)] A lathe for chasing screw threads has the saddle automatically reciprocated and the slide rest maintained against a guide bar by a spring; the bar being pivoted so that at the end of a chasing cut the bar may be tripped to permit the tool to be removed from the cut prior to the return of the saddle for a fresh cut with additional feed. According to the Provisional Specification the automatic chasing mechanism may be constituted as an attachment for existing lathes. The lathe is driven by a reversing motor 6 and the saddle is traversed by the usual lead screw. The slide rest is movable freely on the saddle under the control of a spring 13 that keeps a roller 16 in contact with the bar 14 carried by a pivotal mounting from the bed. The bar is normally maintained parallel to the bed by engagement of a latch 39 with a notch 37 but at the end of a chasing cut an adjustable screw stop 44 is contacted to swing the lever 41 about its pivot 42 to withdraw the latch and allow the spring 13 to push back the slide rest swinging the bar as permitted by the notch 36. At the same time a link 49 actuates a switch 164 to reverse the motor. At the end of the return stroke the saddle engages the arm 47 of a lever, pivoted at 46 to a frame secured upon the bed, and by the arm 45 returns the bar 14 to its initial position in which it is again held by the latch 38. During the return stroke the arm 58 of a lever is held from turning by a latch device 61. whilst a lever 57 is swung by a link 55 connected to the saddle flexing the spring 59 that connects the levers 57, 58. At the end of the stroke the latch device trips and the spring throws the lever 58 to act through a one-way link 63 to return the switch 164 and again reverse the motor. The roller 16 is carried by a bar pivoted to the slide rest and carrying at its other end an adjustable screw stop 18, that in conjunction with an abutment 19 controls the position of the roller and consequently of the slide rest and chaser. At the end of the return stroke an adjustable abutment 31 contacts the notched end of a finger 29 carried by a lever 25 pivoted at 26 and carrying a spring pressed pawl 23 engaging a ratchet wheel 22 on a feed screw, in a bracket 21 carried by the slide rest, and carrying the abutment 19. To increase the amount of cut applied during later traverses of the saddle, a cam 23 attached to the ratchet wheel swings a lever 34 to change the position of the notched finger 29 and so increase the throw of the pawl 23. A link 64 from the saddle actuates a pawl 70 to rotate a ratchet wheel 72 step by step on each return traverse. The ratchet wheel is so set that, after the desired number of traverses, a cam 73 attached to it presents a notch to a projection 74 on a lever 75 that is then moved by a spring to trip a plate 79 itself spring urged to break the motor circuit at 83,2 84 and stop the lathe. A hand lever 85 provides for resetting the ratchet wheel and closing the contacts 83, 84 to restart the motor. This is effected by a pin 88 returning the plate 79, a pin 89 acting on the lever 90 carrying the contact 84 to move the latter to permit the contact 83 to resume its initial position. At the same time a link 76 depresses a lever having a pin 178 that trips the pawl 70 and a pin 96 is engaged by a recess 95 in the lever 85 to trip the detent 98. The wheel 72 and cam 73 are then returned by a spring 173 until a pin 177 is arrested by a pin 176 on a wheel 175 preset according to the number of chasing cuts required. When taper threads are to be cut the latch 38 is adjusted by a screw 142 so that the bar 14 is inclined in one direction or the other to the bed and the top slide is adjusted at 99 to the corresponding angle. A resistance 91 may be put into or out of circuit to cause the idle return stroke of the saddle to take place at higher rate.