GB341646A - Improvements in metal milling machines - Google Patents

Abstract

341,646. Milling screws. McLEOD, R. J., of Power Plant Co., West Drayton, Middlesex. Dec. 4, 1929, No. 37185. [Class 83 (iii).] In a milling - machine, particularly a thread-milling machine in which a hob and the work normally rotate at constant speed but in which the relative velocities may be varied and corresponding relative traverse imparted to the hob for the purpose of avoiding facets on the work, means are provided for automatically restoring the tool and work to predetermined axial and angular relations. The work-piece 5 shown as a double-tapered socket is mounted in a chuck on a spindle 8 which is driven through change speed and reversing gear 11 from a main shaft 10. From a shaft 12 of this gearing, the hob 21 is driven through gears 13, differential gear 17, shaft 18 and bevel gears 19, 20. The hob housing is mounted on a cross slide 24 carried by a longitudinal slide 25. A gear 27 driven from the train 13 drives through reversing bevel gearing 31 a shaft 36 which is connected by a longitudinal shaft and gearing 37, 38<1>, 38<3>, 40 to a lead screw 41 which, as described in Specification 310,240, [Class 83 (iii), Metals, Cutting], imparts a longitudinal movement to the hob to avoid the formation of facets. The hob-rotation is compensated for this movement by means of gearing 33, 34 connected to the differential casing 16. The shaft 36 is also connected by bevel gearing 42 and gears 43 to a cam cylinder 45 having a track 47 actuating a rod 49 provided with adjustable stops 50, 51 coacting with a bar 53 controlling the reversing bevel gearing 31. The bar 53 may also be operated from a handle 55 and its positions are determined by a lever 63 coacting with a notched plunger 66. In operation, the hob saddle 25 is adjusted by hand until the required starting position, such as the position to continue a thread already cut on one half of the blank, is reached. A dead stop is adjusted for this position and the stop 50 is adjusted against the arm 52 with the clutch 31 in neutral position. The cutting of the screw can then be effected, and when the differential movements are required to eliminate the facets the hand lever 55 is operated to engage the forward driving pinion 29. The cam 45 is thus driven and the rod 49 shifted until the stop 51 disengages the clutch. The hob slide 25 is then manually withdrawn, whereupon a projection 60 on this slide rocks the lever 63 to engage the reverse pinion 28 which reverses the lead screw, differential drive and cam 45 until the original positions of these parts are reached whereupon the clutch is agan moved into neutral by the stop 50. In a modification, the cam 45 may be replaced by a disc cam, and in a further modification, Fig. 5, the bar 49 carries a roller coacting with cam strips 73 on a drum 74.