655,243. Grinding screw propellers. RISC, H. W. Dec. 22, 1945, No. 34875. Convention date, Nov. 14. [Class 60] [Also in Group XXII] In a method and apparatus for grinding or milling propellers, either right-hand or left-hand and of any desired pitch, from a single pattern, the work 5 is simultaneously oscillated about its axis of rotation and reciprocated at an adjustable speed along that axis, while the tool 55 is given a radial feed. The machine comprises a base 1, Figs. 1 and 2, with a fixed column 2, a sliding tool carriage 4 duplicated on each side of the column, a work table 8, also duplicated, oscillating about a vertical pivot and a single pattern table 86 oscillater about a vertical pivot in synchronism with the worktable. The uncambered pressure sides of the blades are preferably formed on one side of the machine without using a pattern and then the blank is reversed and the cambered suction sides formed on the other side of the machine using the pattern. Tool head. A tool spindle 57 is driven by an electric motor 56 carried by an arm 59 pivoted at 58 on a shaft 66 and the upper end of the arm is adjustably connected to a rod 60 pivotally attached to a spring-pressed sleeve 67 on a shaft 66. A pair of inclined rods 73, 77 are carried by a transversed carriage 75 on the column 2 and on one of the rods, according to the hand of the propeller, a sliding sleeve 72 is attached to a sleeve 71 sliding on a rod 70 connected to the shaft 66. As the tool carriage is fed forward step-by-step, the sleeve 72 slides down the inclined rod and, through the sleeve 71 and rod 70. turns the shaft 66 so that, during the feed inwards owards he hub, he axis of he ool is always maintained in a plane 81, Fig. 7, normal to the tangential surface of the propeller at the point where the tool is operating; at the beginning of the operation. the tool is set in the plane 81 by adjustment of the carriage 75 against a scale. The tool carriage is fed step-by-step by a pawl 38 and ratchet 37 operated by a crank 34 driven through gearing and chains from a splined shaft 29 and a main shaft 22, Fig. 3; the ratchet is geared to a nut 41 on a feed screw 42 and can also be rotated by a handwheel 44. Work head. The blank 5 is fixed on a shaft 6 indexable by means of a notched sleeve 111 and set-screw 113, Fig. 7, for operating on twothree- or four-bladed blanks. In the form shown in Fig. 1, the shaft 6 is carried on an arm 7 attached to a table 8 which is oscillated by a connecting rod 52 and an adjustable-throw crank 51 on the main shaft. The table is also raised and lowered to give the required pitch to the propeller by rollers 12 on a frame 11 engaging helical rails 13, 14 inside the inner surface of the casing 10. To vary or reverse the pitch, the rails are adjustable about pivots 16 by a lever 18 reading against a scale 19 and are clamped in the adjusted position by screws 15 movable in vertical slots in the casing. In a modified form, Figs. 13-15, the shaft 114 is lowered in a frame 117 by a roller 134 engaging a guide rail 133 carried by a carriage 119 which is moved to and fro on rails 122, 123 by a reversible electric motor rotating a screw engaged by a nut; the motor may be controlled by any suitable means. The work table is rotated by flexible bands 154, 155 wrapped round it in opposite directions and attached to a member 151 sliding on an arm 149 of the carmounted in a carriage 116 raised and riage 116 and having rollers 152 engaging a guide rail on the carriage 119. During the step-by-step radial traverse of the tool, the pitch of the blade can be gradually changed by varying the slope of the guide rail by means of a shaft 139 rotated either by a handwheel or by a pawl operated by the crank 34. Through worm gearing, the shaft 139 rotates screws 126 engaged in nuts 128 at the ends of the rail. Copying mechanism. When forming the cambered suction sides of the blades, a pattern 84 in an oil bath on the table 86 is engaged by a tracer arm 90' having a roller 90. The arm is fixed to a shaft 91 splined in a bearing 94 on the carriage 4 and, as the pattern table is oscillated by a rod 88 on a crank 87 on the main shaft 22, or is moved to and fro in a straight line by means not described, the rotation of the shaft 91 is transferred by a sleeve 96, connecting rod 97, lever 98 and forked lever 100, Fig. 2 and 5, to the sleeve 67 which slides on the shaft 66 and. through the rod 60, rotates the tool arm 59 about its pivot 58. By adjusting the rod 97 in a slot in the sleeve 96 and by varing the point of attachment of the rod to the lever 98, the thickness of the blade can be varied. The tracer arm is fed step-by-step at the rate required by the differences in diameter of the pattern and blank by a feed screw 109 driven from the main feed ratchet through change gearing 105-107. Stop-motions. A rod 45. Fig. 1, attached to the carriage 4, has a disc 46 which at the end of the forward feed of the carriage. operates a switch 48 to stop the driving motor. The switch can be adjusted along a scale 49.