Patent GB-490410-A (GB)
Title: Improvements in machines for manufacturing propeller blades by copying
IPC: B23Q35/10
Filed: 1937-12-31
Abstract: 490,410. Copy-milling machines. RATIE, P. J. P. Dec. 31, 1937, Nos. 36288 and 36289. Convention dates, Jan. 4 and May 11. [Class 83 (iii)] In a machine for copying propeller blades, the pattern and the blade blank are respectively engaged on opposite sides with two tracing rollers and two tools, the axes of oscillation of the tracing rollers and the tools being all different. When making a blade 5 from a pattern 4, Fig. 3, the blade and pinion being rotated synchronously in the direction of arrow f and the two sides of the blade pattern being copied by cutters 13, 13<1> controlled by tracer rollers 9, 9<1> respectively, the positions of the copy roller for various angular positions of the blade 4 are shown in Fig. 4. By plotting angular positions of the blade against displacements of the roller a curve E<2> is obtained and by plotting tangents to this curve a curve V<2> is obtained giving the speed of the roller at different points. V<1> shows the speed curve for a copying system having a rectilinear movement and V3 the curve for the roller 9<1>, Fig. 3. Since it is desirable to employ a copying system which gives the minimum speed variation the linkage employed according to the invention is so arranged that for both systems a speed curve such as V<2> is obtained. Thus, as shown in Fig. 6, the first system comprises a copy roller 9 and cutter 13 mounted on levers 20, 23 which are connected by a bar 22 to form a parallelogram linkage. The second system comprising copy roller 9<1> and cutter 131 is similar but the levers are pivoted above, instead of below the work and pattern. The cutters may be driven from a motor 27 through belts arranged as shown. The length of the lever arms such as 20 is reduced as far as possible in order to obtain the best speed curve V<2>. For a further improvement of the speed curve it is shown that if the roller curve follows a curve C<2> in Fig. 13, it will move uniformly as the blade is rotated at uniform speed. This curve is approximated by arranging the centre of the roller movement at a point 30, the path of the roller being convex in the opposite direction to that of the work. Where the roller path is concave to such direction as in the case of the roller 9<1> in Fig. 18, it is shown that the speed curve is improved by the use of a larger roller as shown. By this modification all the centres of oscillation of the two systems may be arranged below the work and pattern axes as in Fig. 19. All the levers are pivoted on a line MN and the levers carrying the roller 9 and tool 13 of one system are connected by a bar 22 and the levers forming the other system by a bar 22<1>. Counterweights are provided at 34, 34<1>, and other counterweights 35, 35<1> are adjustable on arms 37, 37<1> to maintain the copy rollers against the pattern. The weights 35, 35<1> have centres of gravity which do not lie on the axes of arms 37, 37<1> so that angular adjustment of these counterweights around the pivotal axes 32, 33 is effected by rotating them. The bars 22 may be extended to accommodate cutter levers for shaping a number of blades simultaneously.