Chapter 11 Sawing and Cutoff Machines 165
11.4 Using Power Hacksaws and
Band Saws
Most sawing problems can be prevented
by careful planning and observing a few rules.
These rules apply to both power hacksaws and
band saws.
11.4.1 Blades Breaking
Blades are normally broken when they are
dropped on the work. A loose blade or excessive feed
can cause the blade to fracture. Loose work can also
cause blade damage, as will making a cut on a cor-
ner or sharp edge where the three-tooth rule is not
observed. Broken blades can normally be avoided
with proper machine setup.
11.4.2 Crooked Cutting
Crooked cutting is usually the result of a worn
blade. Remember to reverse the work after replacing
a blade, and start a new cut on the opposite side. See
Figure 11-15. A loose blade or a blade rubbing on a
clamping fi xture will cause the same problem. It can
also be caused by excessive blade pressure on the
work or by worn saw guides.
11.4.3 Blade Pin Holes Breaking Out
This reciprocating blade problem can be caused
by dirty mounting plates or too much tension on the
blade. Worn mounting plates can cause a blade to
twist and strain in such a way that the pin hole will
break out.
11.4.4 Premature Blade Tooth Wear
When this problem occurs, the teeth become
rounded and dull quickly. Insuffi cient feed pressure
(indicated by light, powdery chips) is one of the
major causes of premature blade tooth wear. Exces-
sive pressure (indicated by burned chips) causes the
same problem.
Insuffi cient pressure can be corrected by
increasing cutting pressure until a full curled chip is
produced. If too much pressure is the culprit, reduce
feed pressure until a full curled chip is formed.
Lack of coolant or a poorly adjusted machine
can also cause rapid wear. Correct by following the
manufacturer’s recommendations.
11.4.5 Teeth Strip Off
This failure results when the teeth snap off the
blade. Starting a cut on a sharp corner is a major
cause of this problem. A machine setup with a fl at
starting surface will greatly reduce tooth stripping.
Be sure the work is clamped securely. Loose work
can also cause the teeth to strip, Figure 11-16.
Check the manufacturer’s chart to determine
the proper blade for the job to be done. A blade with
Partial cut
made by worn
blade
Rotate work to
start new cut with
new blade
Cut with
worn blade
Goodheart-Willcox Publisher
Figure 11-15. Never attempt to start a new blade in a cut
made by a worn blade. Reverse the work and start another
cut on the opposite side. Cut through to the old cut.
Correct Incorrect
Goodheart-Willcox Publisher
Figure 11-16. Recommended ways to hold sharp-cornered
work for cutting. A carefully planned setup will ensure that at
least three teeth will be cutting, greatly extending blade life.