GB549912A - Improvements in or relating to method of rifling gun barrels - Google Patents

Abstract

549,912. Broaching. LAPOINTE MACHINE TOOL CO., Ltd. (Lapointe Machine Tool Co.). Sept. 15, 1941, No. 11792. [Class 83 (iii)] Gun barrels are rifled by simultaneously partially broaching all the grooves in the barrel B, Fig. 28, increasing the depth and width of the grooves by successive broaching operations and finally finishing the bore concentrically with the grooves. In one example the barrel B has initially a plain bore of 0.296 inch diameter. It is broached by a first tool, Fig. 1, having a plain pilot portion 40 of 0.295 inch diameter, a series of gradually increasing cutters 41 ... 42 and a non-cutting pilot 43 of 0.303 inch diameter. During this first operation the broach and neck have positive relative rotation according to the spiral lead of the grooves. The metal removed in this operation is that shown at a in Fig. 28. The next broach, Fig. 6, has end pilot portions 50, 53 and cutting portions 51 ... 52, these cutters deepening the grooves by cuts of slightly less width as at b, Fig. 28. The original grooves guide the broach and so positive rotation is not necessary. The third broach is of similar form to the second and widens the grooves to an increased depth as at c, Fig. 28. The fourth broach, Fig. 16, has helical pilot portions 70, 73 and cutting portions 71 ... 72, these cutters making full width cuts of increased depth as at d, Fig. 28. The final broach, Fig. 21, trues up the bore of the barrel to the final diameter of 0.301 inch by removal of metal e, Fig. 28. This broach has pilot portions 80, 82, 84 and round section cutters 81 ... 83.