Section 13. qxd

Band saws,
vertical, horizontal, and universal, are used for cutting off.
The kerf or width of cut is small with a consequently small loss in
expensive material. The teeth of band saws, like those of hacksaws, are
set with the regular alternate type, one bent to the right and the next to
the left; or with the alternate and center set, in which one tooth is bent to
the right, the second to the left, and the third straight in the center. With
high-speed steel saw blades, band speeds range from about 30 ft/min
(10 m/min) for high-temperature alloys to about 400 (120) for carbon
steels. For aluminum and magnesium alloys the speed ranges up to
about 1,300 ft/min (400 m/min) with high-carbon blades. The band
speed should be decreased as the workpiece thickness increases.
Circular saws
are made in a wide variety of styles and sizes. Circular
saws may have teeth of several shapes, as radial face teeth for small
fine-tooth saws; radial face teeth with a land for fine-tooth saws; alter-
nate bevel-edged teeth to break up the chips, with every other tooth
beveled 45
on each side with the next tooth plain; alternate side-beveled
teeth; and one tooth beveled on the right, the next on the left, and the
third beveled on both sides, each leaving slightly overlapping flats on
the periphery of the teeth. The most common high-speed steels for
circular saws are M2 and M7; saws also may have welded carbide teeth
for better performance.
Abrasive cutoff wheels
are made of thin resinoid or rubber bonded
abrasives. The wheels operate at surface speeds of 12,000 to 16,000
ft/min (3,600 to 4,800 m/min). These wheels are used for cutting off
tubes, shapes, and hardened high-speed steel.
9
⁄
16
7
⁄
16
Friction sawing machines
are used largely for cutting off structural
shapes. Peripheral speeds of about 20,000 ft/min (6,000 m/min) are
used. The wheels may be plain on the periphery, V-notched, or with
milled square notches.