Fig. 109.
Fig. 110.
The ordinary method of producing the cutting edges after turning the cutter and serrating it, is to cut away the metal with a file or rotary cutter of some kind forming the cutting edge to correct shape, but paying no regard to the shape of the back of the tooth more than to give it the necessary amount of clearance. In this case the cutter must be softened and reset to sharpen it. To bring the cutting edge up to a sharp edge all around its profile, while still preserving the shape to which it was turned, the pantagraphic engine, shown in [Fig. 108], has been made by the Pratt and Whitney Company. [Figs. 109] and [110] show some details of its construction.[5] “The milling cutter n is driven by a flexible train acting upon the wheel o, whose spindle is carried by the bracket b, which can slide from right to left upon the piece b, and this again is free to slide in the frame f. These two motions are in horizontal planes, and perpendicular to each other.
[5] From “The Teeth of Spur Wheels,” by Professor McCord.
“The upper end of the long lever p c is formed into a ball, working in a socket which is fixed to p c. Over the cylindrical upper part of this lever slides an accurately fitted sleeve d, partly spherical externally, and working in a socket which can be clamped at any height on the frame f. The lower end p of this lever being accurately turned, corresponds to the roller p in [Fig. 109], and is moved along the edge of the template t, which is fastened in the frame in an invariable position.
“By clamping d at various heights, the ratio of the lever arms p d, p d, may be varied at will, and the axis of n made to travel in a path similar to that of the axis of p, but as many times smaller as we choose; and the diameter of n must be made less than that of p in the same proportion.
“The template being on the left of the roller, the cutter to be shaped is placed on the right of n, as shown in the plan view at z, because the lever reverses the movement.