GB549045A - Improvements in or relating to copying lathes - Google Patents

Abstract

549,045. Cutting - screw propellers. BRITISH POWER BOAT CO., Ltd., and BRADBURY, W. P. March 31, 1941, No. 4319. [Class 83 (iii)] In a machine for cutting screw propellers the propeller 67 is mounted on a rotatable work holder with its axis, Fig. 1, at an angle to the axis of rotation so as to reduce the inclination to the face plate of the blade being machined, the tool having a controlled movement axially of the work holder so as to make a series of cuts across a blade face. The bed 10 supports a headstock spindle carrying a face plate 15 from which an arbor 16 projects at an angle of about 15 degrees to the spindle axis. The spindle is oscillated during operation through the angle required to generate one blade, the amplitude being controlled by dogs 39 on the face plate coacting with the reversing switch 38 of the driving motor. The spindle is connected by gearing 14 to a longitudinal shaft 18. A slide rest mounted on the bed comprises a bottom cross-slide 19 carrying a longitudinal tool slide 21 carrying the tool holder 22. This slide is operated by a compound cam 24 arranged on a transverse axis and driven by gearing 60 and bevel gearing 29 from the shaft 18, this gearing including a two-part gear 28, the parts of which are relatively adjustable to control backlash. The cam shaft is thus driven, for a three-bladed propeller, at three times the spindle speed. During a forward oscillation of the work the required axial copying movement is imparted to the tool by the cam 24 which is returned during the backward movement. A pinion 38 on the cam-shaft acts through a quadrant 54 to operate pawl-and-ratchet mechanism driving the cross feed-screw 44 to impart radial feed to the tool and to bring the roller on to a different part of the cam. The arbor has three keyways at 120 degrees for positioning successive blades. The tool may be inclined for cutting propellers with wide blades. The tool may be replaced by a milling-cutter driven by a motor on the tool-holder. The cam may be machined from a master blade by interchanging the positions of the tool and follower. In a modification, the compound cam may be replaced by a large cam having a number of pairs of cam surfaces 46, Fig. 6, each pair corresponding to one cut across a blade face, the face being finished after one revolution of the cam shaft. The movements of cam roller 47 are transmitted to the tool by lever mechanism. The shapes of the cams are preferably determined by setting up a master blade and scribing lines on cam blanks by a scriber fitted in place of the cam follower.