Tc 9-524 fundamentals of machine tools

3-10

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TC 9-524
THE PORTABLE HACKSAWING MACHINE
The portable hacksawing machine (Figure 3-24) is not
designed to be hand-held, but to lock onto the workpiece with
a self-contained vise. This saw has a built-in electric motor
that causes a power hacksaw blade to reciprocate at a fixed
speed of 115 strokes per minute. The machine is capable of
cutting solid steel 3 inches square and at an angle to 45°. This
saw can be used in a horizontal, angular, or vertical position,
having an adjustable counterbalance to compensate for
operating the sawing machine in a vertical position. A 10-inch
power hacksaw blade is used with this machine, producing a
4-inch stroke. A tension screw permits increasing or
decreasing the blade pressure with each cut. The portable
hacksawing machine will support itself when fastened very
securely to a stationary workpiece, using the self-contained
vise.
To operate the portable hacksawing machine, insert a
power hacksaw blade of 18, 24, or 32 teeth per inch,
depending on the material to be cut. Then, check the
adjustment of the tension screw and the adjustment of the
counterbalance lever. Turning the tension screw clockwise
will increase the amount of lift the hacksaw blade makes on
each return stroke and will increase the downward pressure of
the blade on each cutting stroke. Counterclockwise rotation of
the screw will decrease the lift and pressure. This control
should be adjusted to cause the hacksaw blade to lift 1/8 inch
on each return stroke to provide maximum cutting speed and
efficiency. The counter balance lever controls the downward
pressure exerted upon the hacksaw blade by the weight of the
saw frame. By moving the counterbalance lever to the left, the
pressure is decreased. Moving the lever to the right increases
the pressure. Mount the workpiece squarely or angularly in the
vise, depending on the type of cut desired. Start the sawing
machine and observe the cutting action. If the machine strains,
the blade pressure may be too heavy.
If the machine cuts very slowly, increase the pressure.
Continuously check the power hacksaw blade for sharpness. If
the blade is dull, it should be replaced. When the machine cuts
completely through the material, the saw frame will fall and
trip the motor switch, stopping the saw.
When the sawing machine is used in the vertical position,
the counterbalance lever must be positioned in the farthest
right notch of the guide bar ratchet to compensate for the lack
of gravitational pressure normally applied to the blade by the
saw frame. This practice should be attempted only if the
workpiece can be clamped very securely in the vise and
cannot be wrenched loose during vertical sawing, or damage
to personnel or equipment could occur .