GB406892A - Improvements in screw-thread cutting dies - Google Patents

Abstract

406,892. Making chasers. MILLERCHIP, J., 51, Finlayson Street, Lane Cove, and LAMBERT, T. M., 67, Whiting Street, Artarmon, both in New South Wales, Australia. May 23, 1933, No. 14863. Convention date, June 27, 1932. [Classes 83 (ii) and 83 (iii).] In making screw-cutting dies or chasers for use in a die-head, a number of die blanks are mounted in a holder so as to be approximately radial and spaced apart, with the trailing edges of the cutting faces nearer the axis of the holder than the leading edges, and the teeth are then cut on said faces by rotating a screw tap in the space between the faces. In making block dies of the form shown in Fig. 6, a disc 23, Fig. 1 is provided with four approximately radial slots 21 and four radial tapped holes 22, after which the centre is drilled out at 24 almost to the bases of the slots to a diameter to suit the thread to be produced by the dies. The disc is then severed along lines x-x to produce four die blanks 25, Fig. 5, which are mounted in a cylindrical holder 32 for producing the cutting faces. Set-screws 35, or alternatively packing pieces or eccentric surfaces on the holder, adjust the outer arcuate surfaces 23 of the dies eccentrically with regard to the holder. Screws 34 passing through axial slots 33 in the holder secure the dies in this position and the forward ends of the cutting surfaces 30 are bevelled by a chamfering drill &c. to produce the entering ends 36, Fig. 6, of the dies. The eccentricity of the dies in the holder is then reduced, by adjustment of the screws 35 or by changing the packing pieces or using a holder with different eccentric surfaces, a clearing drill is passed through the aperture 37 between the dies and the threads 38 are cut by means of a tap having the same diameter as the work to be produced by the dies, or slightly oversize. If the eccentricity of the dies in the holder is very slight, the use of the clearing drill may be dispensed with. The dies are next removed from the holder 32 and the lips 27 and corners 29, Fig. 6, are removed, after which they are hardened and finished. In producing slab dies of the form shown in Fig. 13, four blanks 40, Fig. 9, are mounted in channel shaped slots in holders 46 on a disc 43 having studs 44 for attachment to a support. Lugs on the holders engage the inclined slots 41 in the dies and the latter are clamped in position by a ring 52 and studs 51. Each holder 46 is pivoted to the disc 43 at a point adjacent the central aperture 45 therein and is set to give the die a non-radial position by means of a pointer 49 coacting with a set of scales 50 on the disc 43. When each die is set to make an angle of, e.g. ¢‹ with a radius, the inner ends of the dies are bored out to the correct diameter and then tapped by a tap of the same diameter as the work to be produced by the dies, or slightly oversize. The holders 46 are then adjusted to increase the eccentricity of the dies, e.g. to angles of 2‹ with radii of the plate 43, and a chamfering tool is introduced between them to produce the bevelled entering teeth 55, Fig. 13. To produce the outer cam surfaces 47 on the dies, the holders 46 are adjusted to an angle of 5‹-10‹ to a radius and the plate mounted in a lathe. The dies are then removed from the holders and the cutting edges provided with rake as at 56, Fig. 13, after which the dies are hardened and finished. The adjustable holders 46 may be replaced by fixed non-radial slots in a disc, the dies being removed, after the teeth have been cut, to separate holders for chamfering and the formation of the cam-surfaces.