The driving surface of a propeller blade is made up of straight line elements radiating from the axis of the propeller. This fact enables a true and smooth surface to be machined on the blade by means of the planer. The driving surface of the blade is generated by a straight line moving at a uniform rate along the axis of the propeller and at the same time revolving about this axis at a uniform angular rate.

A device has been perfected which rests on the planer table and holds a single blade in such position that an element of the blade is parallel to the direction of motion of the table. This device has a feeding arrangement which gives the blade such a combined motion of translation and revolution that each of its elements in succession is brought into a position which the too1 will follow as the table moves.

In the foundry, a propeller-blade mould is swept up in loam by a sweep, the edge of which is raised and revolved at the same time to generate the driving surface of the blade.

Fig. 195.   Shaper.

Fig. 195. - Shaper.