Machining Fundamentals
194
Many techniques have been developed for prop-
erly mounting and tensioning blades. Use a torque
wrench and consult the manufacturer’s literature. If
the information (proper torque for a given blade on
a given machine) is not available, the following
methods can be used:
• Tighten the blade until a low musical ring is
heard when the blade is tapped lightly. A
high-pitched tone indicates that the blade is
too tight. A dull thud means the blade is too
loose.
• The shape of the blade pin hole can serve as
an indicator of whether the blade is tensioned
properly. When proper tension is achieved,
the pin holes will become slightly elongated,
Figure 12-7.
The blade will become more firmly seated after
the first few cuts and will stretch slightly. The blade
will require retensioning (retightening) before fur-
ther cutting can be done.
12.2.3 Cutting with a Power Hacksaw
Measure off the distance to be cut. Allow ample
material for facing if the work order does not spec-
ify the length of cut. Mark the stock and mount the
work firmly on the machine, Figure 12-8.
If several sections are to be cut, use a stop gage,
Figure 12-9. Apply an ample supply of coolant if the
machine has a built-in coolant system.
12.3 POWER BAND SAW
The horizontal band saw, Figure 12-10, is fre-
quently referred to as the cutoff machine. It offers
three advantages over the reciprocating hacksaw:
• Greater precision—The blade on a band saw
can be guided more accurately than the blade
on the reciprocating power saw. It is common
practice to cut directly “on the line” when
band sawing, because finer blades can be
used.
Mounting
pin
Elongated
mounting pin
hole
Saw
frame
Figure 12-7. Pin holes on a properly tensioned blade will be
slightly elongated, rather than round.
Avoid—
make sure movable
jaw of vise fits
solidly against work
Solid
vise jaw
Movable
vise jaw
Figure 12-8. If the work is not clamped solidly, it will twist and
the blade will bind and be ruined in the first few seconds of use.
Figure 12-9. A stop gage is used when several pieces of the
same length must be cut. Set it high to permit the work to fall
free when completely cut.
Set stop gage
high enough to
allow cut piece
to fall away
from blade