The cutting speeds given above are what may be used with the best grades of tool steel, such as Jessop's; but by using air-hardening or tungsten steels, the speed of cutting may be very much increased over the values given above. These high-speed steels are rapidly coming into favor, more especially for heavy roughing cuts.

With the aid of these steels, the cutting speeds have been increased, and the chip is made heavier in both depth and feed, up to the point where the lathe refuses to carry the load. The ability of this quality of steel to stand without injury, the high temperatures resulting from the fast feeding, is the feature which enables it to perform the work at this rate.

For what are now known as the high-speed steel tools, the speeds for the different metals mentioned will be as follows:

Usually an increase in speed must be accompanied by a reduction in the feed-that is, in the number of revolutions of the work per inch of movement of the tool. The following directions will be proper in this respect:

Roughing cuts on soft cast iron may be made with a feed as coarse as 4 to 5 per inch, with a strong round-nosed tool.

Roughing cuts on soft machine steel forgings, 5 to 8 per inch.

Sizing cuts on soft cast iron, 12 to 16 per inch.

Sizing cuts on soft machine steel, 16 to 20 per inch.

Finishing cuts on soft cast iron, with a narrow-point tool, 15 to 25 per inch.

Finishing cuts on soft machine steel, with a narrow-point tool, 20 to 40 per inch.

Finishing cuts on soft cast iron, with a wide point, practically a straight-faced tool with the corners slightly rounded, 1 to 4 per inch.

Under the same circumstances, for a soft machine steel, 4 to 8 per inch.

Brass will be turned with feeds of from 10 to 40 per inch, according to the kind of cut and shape of the tool.

Fiber will stand a heavy feed in proportion to the speed.