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Thread Cutting Exercise - OTMT SC4 User Manual And Installation Manual

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Thread Cutting Exercise

For this exercise, select a piece of ¼" diameter
stock at least 3-4" long and mount it in the
chuck with about 1-1/2" extending from the
chuck. This is a greater extension than
normally might be used for ¼" stock, but it
provides extra distance away from the face of
the chuck for safety until you become familiar
with the threading procedure.
If you don't have ¼" diameter stock on hand,
use the next larger diameter you have
Commercially manufactured bolts typically
have a diameter a few thousandths of an inch
less than the nominal bolt diameter. Thus a
diameter of 0.245 will be used in this exercise.
1. Use a facing cut to form a smooth end on
the workpiece.
2. Use a turning tool to turn down a length of
about ¾" to a diameter of 0.245"
Check the diameter with a caliper or
Next, perform the following steps to zero the
calibrated dials:
1. Mount a thread-cutting tool in the toolholder.
2. Adjust the angle of the compound slide so
that the 30
reference mark at the left side of the
compound base.
3. Bring the tip of the tool about 1/8" from the
side, and close to the end of the workpiece.
4. Loosen the toolpost handle and rotate the
toolpost until the tip of the tool is square to
the side of the workpiece. This is best done
using a "fishtail" gage.
5. Rotate the cross-slide handwheel a partial
turn until the ball on the handle is pointing
straight up. This position will serve as a
convenient reference point later on.
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6. Hold the cross-slide handwheel in place
and rotate the calibrated ring until it is set
to "0".
7. Rotate the compound handwheel until the
tip of the tool just touches the side of the
8. Hold the compound handwheel in place
and rotate the calibrated ring until it is set
to "0".
This procedure zeros the calibrated dials to the
surface of the workpiece to facilitate measuring
the depth of the threading cut.
Next, a test pass is made to verify the proper
thread spacing.
1. If not already done, set up the gear train for
a 20 TPI thread.
2. Apply light pressure to the half-nut (power
feed) lever.
3. Rotate
clockwise while maintaining pressure on
the half-nut lever.
4. When the leadscrew threads mesh with the
gear of the half-nut lever, the lever will drop
into the engaged position.
5. Continue rotating the chuck about 5 or 6
6. The tip of the cutting tool should cut a
shallow spiral groove into the side of the