Page:Practical Treatise on Milling and Milling Machines.djvu/100

94 cut end mills are used for milling shallow recesses in a surface where there has been no hole previously bored for starting the cut, for milling squares on the ends of round shafts, and other similar work. This form of mill has fewer teeth, and is, therefore, better adapted to taking heavy cuts than the regular solid or shell end mills. Slotting end mills with two lips, or cutting edges, are especially adaptable to fast milling of deep slots from the solid where there has been no hole previously drilled for starting the cut. In fact, these mills embody both the principles of a drill and end mill. A depth of cut equal to one-half the diameter of the mill can usualy be taken from solid stock. The best results are obtained by maintaining a high surface speed.

End mills with right-hand teeth usually have a left-hand spiral, and those with left-hand teeth have a right-hand spiral. By having the direction of spiral opposite to the faces of the teeth the thrust of the spiral tends to force the shank of the mill solidly into the spindle, although there is little danger of pulling out the mill when the teeth and spiral are of the same hand.

T Slot Cutter. The T slot cutter has teeth upon its periphery, and alternating teeth on the sides. The teeth are neither parallel nor perpendicular to the axis of the cutte,r but are at some oblique angle. The cutter may have more than one angle.

These cutters can be mployed on a variety of work, as cutting the edge of a piece to a required angle and milling teeth of cutters and reamers. Where the nature of the work is such, as in dovetailing a piece, that the cutter cannot be fastened to the arbor with a nut, the cutters are furnished with threaded holes, or made solid on a taper shank.

Formed Cutters. Formed Cutters constitute and important group, their cutting edge usually being an irregular outline. These cutters have teeth that are relieved so that they may be resharpened repeatedly or until the teeth are too slender to permit further grinding, without changing the original form as long as the teeth are ground radially on their faces. Illustrations of this type are shown on page 91, and