GB164048A - Method of making milling cutters - Google Patents

Abstract

164,048. Marks, E. C. R., (Pratt & Whitney Co.). Dec. 3, 1919. Milling-cutters.-In making a backed-off milling- cutter of the kind having axially-inclined non- rectilinear teeth, the blank A is milled by a forming cutter S which is fed downwards to produce the backing off whilst the blank is slowly rotated. The forming cutter S, Fig. 14, may have teeth parallel to the axis but bevelled or otherwise ground on their front faces to helicoids or, as shown in Fig. 16, may be made with generally helical teeth. The direction of inclination of the teeth must be the same on both cutters, whilst the degree of inclination is preferably the same, though the forming cutter is generally of much smaller diameter. The degree of relief of the forming cutter must bear to that of the final cutter a ratio which is the inverse of the ratio of the respective degrees of inclination of their teeth. and is preferably therefore 1 : 1; it is also preferred to make both cutters with the same number of teeth, as the same backing-off cam can then be used for both. To allow for the slight error which arises from the fact that the forming cutter cuts its maximum depth in a plane perpendicular to the outer face of a tooth of the finished cutter and not in a plane containing the axis of that cutter, the forming cutter is backed-off by means of a lathe tool V, Fig. 28, slightly tilted as shown; the profile of the tool V is that of the contour to be cut. In the case of a finished cutter with undercut teeth, the necessary correction of forming cutter is similarly obtained, the angle of tilt required being greater. The finished cutter may alternatively be cut by a lathe tool X, Fig. 35, with an inclined front face 36. This tool X is obtained by the use of a tool W (as shown in Fig. 33) set with a cutting face 34 parallel to the cuting face 35 of the tool X and reciprocated parallel to the face 36. The tool W is itself produced by milling with the forming cutter S in the ordinary way; or it may be made by a reciprocating cutter Y, Fig. 36, with an inclined upper face as shown in Fig. 37 but formed with the correct contour at a transverse sectional plane perpendicular to its direction of reciprocation.