## Table IV. Speeds And Feeds For Milling Cutters

 Material Speed (ft. per min.) Feed (in. per min.) Soft cast iron 60 1 1/2 Hard cast steel 40 l Wrought iron 45 1 Soft machine steel 36 3/4 Hard machine steel 24 1/2 Tool steel, annealed 30 1/2 Tool steel, not annealed 20 1/4 Soft brass 120 2 3/4 Hard brass 100 2 1/4 Bronze 80 1 1/2 Bronze, gun metal 60 5/8 Vulcanized fiber (gray and red) 60 6

reduce to a speed and feed of safety. Sometimes the speed must be reduced, and yet the feed need not be changed.

The average speed on wrought iron and annealed steel, using carbon steel cutters, is perhaps 40 feet per minute, which gives about sixty turns per minute with mills 2 1/2 inches in diameter. The feed of the work for this surface speed of the mill can be about 1 1/2 inches per minute, and the depth of the cut about 1/16 inch. In cast iron, a mill can have a surface speed of about 50 feet a minute while the feed is 1 1/2 inches per minute and the cut 3/16 inch deep. In tough brass, the speed may be 80 feet, the feed the same as in cast iron, and the chip 3/32 inch.

As small mills cut faster than large ones, an end mill, for example, 1/2 inch in diameter, can be run about 400 revolutions per minute with a feed of 4 inches.

Addy, an English authority, gives as a safe speed for cutters of

6 inches diameter and upward:

Steel, 36 ft. per min., with a feed of \ in. per min. Wrought iron, 48 ft. per min., with a feed of 1 in. per min. Cast iron, 60 ft. per min., with a feed of I 2/3 in. per min. Brass, 120 feet per min., with a feed of 2 2/3 in. per min.

He also gives a simple rule for obtaining the speed: The number of revolutions which the cutter should make when working on cast iron equals 240 divided by the diameter in inches.

In Table IV are given the average speeds in feet per minute of the periphery of the cutter, and the rate of feed in inches per minute for various materials.

Tables V, VI, VII, and VIII, have been prepared by the Brown and Sharpe Manufacturing Company, to give the speed, feed, and depth of cut that can be obtained with a machine similar to that illustrated in Fig. 224. It is understood that these speeds

♦Attention is called to the seemingly slow speed and fast feed for vulcanized fiber. Practice, however, proves it to be correct.