Chapter 12 Sawing and Cutoff Machines
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12.4.4 Premature Blade Tooth Wear
When this problem occurs, the teeth become
rounded and dull quickly. Insufficient feed pressure
(indicated by light, powdery chips) is one of the major
causes of this condition. Excessive pressure (indicated
by burned chips) causes the same problem.
Insufficient pressure can be corrected by increas-
ing cutting pressure until a full curled chip is pro-
duced. 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.
12.4.5 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 flat
starting surface will greatly reduce tooth stripping.
Be sure the work is clamped securely; loose work
can also cause the teeth to strip, Figure 12-16.
Check the manufacturer’s chart to determine the
proper blade for the job to be done. A blade with
teeth too fine will clog (load) and jam, causing the
teeth to shear off. A blade that is too coarse (less
than three teeth cutting) will cause the same prob-
lem. Make sure the blade is properly mounted and
cutting on the power stroke.
12.5 CIRCULAR METAL-CUTTING
SAWS
Metal-cutting circular saws are found in many
areas of metalworking. Primarily production
machines, these saws are divided into three classifi-
cations:
• Abrasive cutoff saw.
• Cold circular saw.
• Friction saw.
An abrasive cutoff saw, Figure 12-17, cuts mate-
rial using a rapidly revolving, thin abrasive wheel.
Most materials—glass, ceramics, and metals—can
be cut to close tolerances. Hardened steel does not
require annealing to be cut. Special heat-resistant
abrasive wheels are available for high-speed cutoff
of hot stock.
Abrasive cutting falls into two classifications,
dry and wet. Wet abrasive cutting, while not quite
as rapid as dry cutting in some applications, pro-
duces a finer surface finish and permits cutting to
close tolerances. The cuts are burn-free and have
few or no burrs. Dry abrasive cutting does not use a
coolant and is used for rapid, less-critical cutting.
A cold circular saw, Figure 12-18, makes use of
a circular, toothed blade capable of producing very
accurate cuts. Large cold circular saws can sever
round metal stock up to 27″ (675 mm) in diameter.
A friction saw blade may or may not have teeth.
The saw operates at very high speeds (20,000 sur-
face feet per minute or 6000 m per minute) and actu-
ally melts its way through the metal.
Teeth are used primarily to carry oxygen to the
cutting area. These machines find many applica-
tions in steel mills to cut red-hot billets (sections of
semifinished steel).
12.6 POWER SAW SAFETY
• Never attempt to operate a sawing machine
while your senses are impaired by medication
or other substances.
Partial cut
made by worn
blade
Rotate work to
start new cut with
new blade
Cut with
worn blade
Figure 12-15. 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
Figure 12-16. 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.