In cutting T-slots in various parts of machines, such as milling machine carriages, etc., it is necessary to use a form of shank mill known as a T-slot cutter. Fig. 243 shows the ordinary form of T-slot, while Fig. 244 shows the cutter. A portion of the stock below the teeth is cut away, as shown at A A in the sectional view, Fig. 245. This is necessary in order to back off the teeth on the sides of the cutter for clearance, and to do away so far as possible with unnecessary friction when the cutter is working.

T-slot cutters are usually made 1/32 inch larger in diameter than the size designated on the cutting portion, to allow for sharpening; that is, a mill intended for cutting a slot 1/2 inch wide is made 1/2 + 1/32 or 17/32 inch in diameter, unless intended for cutting a slot to given dimensions.

It is advisable to harden mills of this description the entire length of the neck, especially if that is of small diameter; for otherwise they will be very likely to spring when in use. After hardening, the neck should be drawn to a blue color, while the cutting part should be drawn to a straw color.

When grinding end mills, the shank in all cases should be ground first to fit the collet or holder, allowing it to enter far enough to key out readily, but yet not enough to allow the shoulder above the tenon to strike the shoulder in the collet.

Fig. 243. Section Showing Typical T-Slot.

Fig. 244. T-Slot Cutter Caurtesy of Becker Milling Machine Company, Hyde. Park, Massachusette.

After grinding the teeth for clearance on the diameter, the teeth on the end should be ground. Most universal and cutter grinders are provided with a fixture for holding the mill by the shank while grinding these teeth, Fig. 246.