Chapter 12 Sawing and Cutoff Machines
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High-speed cutting requires use of a coolant.
Coolant reduces friction, increases blade life, and
prevents chip-clogged teeth. Cast iron and some
brass alloys, unlike most materials, do not require
coolant.
A swivel vise permits angular cuts to be made
quickly. See Figure 12-4.
12.2.1 Selecting a Power Hacksaw Blade
Proper blade selection is important. Use the
three-tooth rule—at least three teeth must be in con-
tact with the work. Large sections and soft materials
require a coarse-tooth blade. Small or thin work and
hard materials require a fine-tooth blade.
For best cutting action, apply heavy feed pres-
sure on hard materials and large work. Use light
feed pressure on soft materials and work with small
cross sections, Figure 12-5.
Blades are made in two principal types: flexible-
back and all-hard. The choice depends upon use.
Flexible-back blades should be used where
safety requirements demand a shatterproof blade.
These blades should also be used for cutting odd-
shaped work if there is a possibility of the work
coming loose in the vise.
For a majority of cutting jobs, the all-hard blade
is best for straight, accurate cutting under a variety
of conditions.
When starting a cut with an all-hard blade, be
sure the blade does not drop on the work when cut-
ting starts. If it falls, the blade could shatter and fly-
ing pieces cause injuries.
Blades are also made from tungsten and molyb-
denum steels, and with tungsten carbide teeth on
steel alloy backs. The following “rule-of-thumb” can
be followed for selecting the correct blade:
• Use a 4-tooth blade for cutting large sections
or readily machined metals.
• Use a 6-tooth blade for cutting harder alloys
and miscellaneous cutting.
• Use 10- and 14-tooth blades primarily on light
duty machines where work is limited to small
sections requiring moderate or light feed
pressure.
12.2.2 Mounting a Power Hacksaw Blade
The blade must be mounted to cut on the power
(back) stroke. The blade must also lie perfectly flat
against the mounting plates, Figure 12-6. If long life
and accurate cuts are to be achieved, the blade must
be properly tensioned.
Figure 12-4. A swivel vise permits angular cuts.
Heavy feed pressure
Large work or
hard metals
Light feed pressure
Small work or
soft metals
Figure 12-5. Apply heavy feed pressure on hard metals and
large work. Use light pressure on soft metals and work with
small cross sections.
Blade must be
seated solidly
against mounting
plate
Direction
of cut
Tap blade lightly
and listen to ring
Figure 12-6. The blade must be adjusted to cut on the back
stroke. Make sure it is perfectly flat against the mounting plates
before tensioning. Tighten the blade until a low musical ring is
heard when the blade is tapped with a small hammer. Since
blades have a tendency to stretch slightly after making a few
cuts, tension should be checked and, if necessary, adjusted.