Chapter 11 Sawing and Cutoff Machines 161
11.2 Power Hacksaw
A power hacksaw, Figure 11-3, uses a recipro-
cating motion to move the blade across the work.
The blade cuts on the backstroke. There are several
types of feeds available.
Positive feed produces an exact depth of cut on
each stroke. The pressure on the blade varies with
the number of teeth in contact with the work.
Defi nite pressure feed yields a pressure on the
blade that is uniform regardless of the number of
teeth in contact with the work. The depth of the cut
varies with the number of teeth contacting the work.
This condition prevails with gravity feed.
Feed can be adjusted to meet varying conditions.
For best performance, the blade and feed must be
selected to permit high-speed cutting and heavy feed
pressure with minimum blade bending and breakage.
Standard power hacksaws are available in
sizes from 6″ × 6″ (150 mm × 150 mm) to 24″ × 24″
(900 mm × 900 mm). The saws can be fi tted with many
accessories. A swivel vise permits angular cuts to be
made quickly, Figure 11-4. Quick-acting vises allow
faster manual clamping of the workpiece. Power
stock feed, power clamping of work, and automatic
cycling can automate the cutting operation. Auto-
matic cycling moves the work out the required dis-
tance, clamps it, and makes the cut automatically. The
cycle is repeated on completion of the cut.
High-speed cutting requires use of a coolant.
Coolant reduces friction, increases blade life, and pre-
vents chip-clogged teeth. Cast iron and some brass
alloys, unlike most materials, do not require coolant.
11.2.1 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 fi ne-tooth blade.
For best cutting action, apply heavy feed pres-
sure on soft materials and large work. Use light feed
pressure on hard materials and work with small
cross sections, Figure 11-5.
Blades are made in two principal types: fl exible-
back and all-hard. The choice depends on use.
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Figure 11-3. An industrial reciprocating power hacksaw.
Worakit Sirijinda/Shutterstock.com
Figure 11-4. A swivel vise permits angular cuts.
Heavy feed pressure
Large work or
soft metals
Light feed pressure
Small work or
hard metals
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Figure 11-5. Apply heavy feed pressure on soft metals and
large work. Use light pressure on hard metals and work with
small cross sections.