Fig. 48
milled on two parallel sides at once, as milling the heads
of bolts, nuts, tongues, etc., straddle mills can be used
most advantageously.
These cutters are also made with interlocking side teeth for milling slots to standard width. The teeth interlock, as shown in Fig. 48, and the standard width of the slot is maintained by packing washers between the cutters.
Face Milling Cutter. This cutter may be likened to a disk with teeth on the periphery and on one face. It is fastened at the end of the machine spindle, and the teeth on the flat face come in full contact with the work, Fig. 48 w hile only a small length of the teeth on the periphery act on the piece. There are cutters of this type made which have no teeth on the periphery; an example of one is shown in Fig. 49.
End Mill. This type of cutter, like the face milling cutter, has teeth on the periphery and at the end.
End mills are used for a large variety of light milling operations, such as milling cuts on the periphery of pieces, cutting slots, and facing narrow surfaces. They are made in four distinct styles, the ordinary solid end mill, with either straight or spiral teeth, the end mill with centre cut, the slotting end mill with two lips, and the shell end mill with either straight or spiral teeth.
Fig. 49
The ordinary solid end mill has its teeth cut on the same piece of steel that forms its shank; in reality, the space where the teeth are cut is only a continua- tion of the shank. The shell end mill has a hole through the centre so it can be mounted on the end of an arbor. This type should be used whenever Fig. 49 possible, because it is cheaper to replace when worn out or broken than the solid mill. End mills with centre cut differ from the others in that the end teeth are designed to cut at the inner ends, while these teeth in ordinary end mills have no cutting edge at the centre. Centre
