Page:Practical Treatise on Milling and Milling Machines.djvu/101

Rh Figs. 50 and 51 show the extent to which they can be ground without changing the form of the teeth. Formed cutters with teeth relieved so that they may be ground on the faces without changing the contour, should be employed wherever the requirements of work demand that the original form of the cutter be maintained, as in manufacturing duplicate irregular pieces.

With this style of cutter, exact duplicate pieces of irregular outline can be produced far more cheaply than by any other method. In fact, no invention has so revolutionized the manufacturing of small parts of machinery and tools. Concave and convex cutters, cutters for grooving taps, corner rounding cutters, gear cutters, etc., are made with teeth relieved so that they may be sharpened repeatedly without changing the contour. Cutters for producing irregular outlines are also made with plain milling cutter type of teeth, but it is necessary to have special grinding machines for them, and the concave cutters have to be made interlocking to preserve the size of circle. Cutters of this type are shown on page 91.

Fly Cutter. The most simple cutter for producing a form is the fly cutter, shown in Fig. 52. This cutter is very similar to a planer tool but is held in an arbor and rotated instead of being clamped in a tool head. It can hardly be classed with the cutters previously mentioned,