Using the Thread-Cutting Stop
Because of the lost motion caused by the play
necessary for smooth operation of the change gears,
lead screw, half-nuts, and so forth, you must withdraw
the thread-cutting tool quickly at the end of each cut.
If you do not withdraw the tool quickly, the point of
the tool will dig into the thread and may break off.
To reset the tool accurately for each successive
cut and to regulate the depth of the chip, use the
First, set the point of the tool so that it just touches
Figure 6-92.--Adjustable thread-cutting stop mounted on
the work, then lock the thread-cutting stop by turning
carriage saddle (clamped to dovetail).
the thread-cutting stop screw (A of fig. 6-92) until the
When you are ready to take the first cut, run the tool
Engaging the Thread Feed Mechanism
rest back by turning the cross-feed screw to the left
several times, and move the tool to the point where
When cutting threads on a lathe, clamp the
the thread is to start. Then, turn the cross-feed screw
half-nuts over the lead screw to engage the threading
to the right until the thread-cutting stop screw strikes
feed and release the half-nut lever at the end of the cut
the thread-cutting stop. The tool is now in the original
by means of the threading lever. Use the threading
position. By turning the compound rest feed screw in
dial to determine when to engage the half-nuts so the
0.002 inch or 0.003 inch, you will have the tool in a
cutting tool will follow the same path during each cut.
position to take the first cut.
When an index mark on the threading dial aligns with
For each successive cut after returning the
the witness mark on its housing, engage the half-nuts.
carriage to its starting point, you can reset the tool
For some thread pitches you can engage the half-nuts
accurately to its previous position. Turn the
only when certain index marks are aligned with the
cross-feed screw to the right until the shoulder of the
witness mark. On most lathes you can engage the
screw (A) strikes the stop (B). Then, you can regulate
half-nuts as follows:
the depth of the next cut by adjusting the compound
rest feed screw as it was for the first chip.
For all even-numbered threads per inch, close
Be sure to use a coolant or lubricant while cutting
the half-nuts at any line on the dial.
the threads. This will help to cool the work and to
wash the chips away.
For all odd-numbered threads per inch, close
the half-nuts at any numbered line on the dial.
For cutting an internal thread, set the adjustable
thread-cutting stop with the head of the adjusting
screw on the inside of the stop. Withdraw the tool by
For all threads involving one-half of a thread in
moving it toward the center or axis of the lathe.
each inch, such a 11 1/2, close the half-nuts at
any odd-numbered line.
cross-feed screw in place of the thread-cutting stop, if
you desire. To do this, first bring the point of the
Cutting the Thread
threading tool up so that it just touches the work; then
adjust the micrometer collar on the cross-feed screw
to zero. Make all adjustments for obtaining the
After setting up the lathe, as explained previously,
desired depth of cut with the compound rest screw.
take a very light trial cut just deep enough to scribe a
line on the surface of the work, as shown in view A of
Withdraw the tool at the end of each cut by turning the
cross-feed screw to the right one turn, stopping at
that the lathe is arranged for cutting the desired pitch
zero. You can then adjust the compound rest feed
screw for any desired depth.