On Mon, 19 Dec 2011 06:17:00 -0500, "Wild_Bill"
wrote:

As DoN has mentioned, using a DI and turning the spindle with the carriage
feed engaged will show if there are errors in the selected gear set.
I generally just rotate the chuck the number of turns equal to the TPI to
make sure the travel is 1.00".

Before I assembled a variable speed drive, I was using a hand crank fitted
into the back/left end of the spindle for short threaded sections such as
lens adapters which may only use 3-4 turns of thread.
When cutting up to a shoulder, the variable speed drive is a huge benefit.

For a fine thread, using a hand crank is fairly easy work, but there are
several other required additional steps which make cutting the thread
successful.

This is a basic outline:
Unplug the power cord for hand crank method
Setup the compound at about 29 to 29.5 degrees
Cutting lubricant applied to work area
Setting the cross feed dial to zero for the scratch cut
Set the compound dial to zero for the scratch cut
Make the first pass scratch cut
Backing out the cross feed enough to clear the workpiece
Reverse feed to locate the carriage for a second pass (by hand if using a
crank)
Set the cross feed dial back to zero for the second pass
Advance the compound for a reasonable cut (depending upon hand or power cut)
Make the second pass with cutting lube
Repeat from Backing out the cross feed

It helps to have a (quality) nut of the desired thread nearby to use as a
gage.. otherwise, there are cutting depth specs on on threading gages for
setting up the cutting tool prior to threading (perpendicular to the
workpiece axis).
A quality nut would be one that doesn't rattle when run onto a quality tap..
which will insure that the resulting thread will fit any other standard nut
of that size/pitch.

Adhering to the thread specs will generally prevent cutting too deep,
although getting familiar with a machine generally includes seeing how well
it responds to operator input, so when nearing the final recommended depth
of the cut, trying the nut can prevent undercutting and the need to start
over.

The edges of the thread crests can be sharp and possibly a little rough..
removing the hand crank and running the spindle at a reasonable speed will
allow the operator to wire brush the freshly-cut thread (carbon steel brush
bristles for a steel workpiece) and/or run some emery cloth over the area
(apply a protective cover/shop rag over the ways to keep any shedded
abrasive off them).
A 3-sided file can also be used to very lightly chase along the thread to
break the sharp edges of the thread.

Thanks. Pretty much all that I did except for the indicator thing.

I could only find a scanty reference to the depth of each pass - they
recommended 0.003" on the compound. That makes it about 0.0025" depth
of cut per pass. For the 1/2"-20 the depth of thread is about 0.060"
so that is about 25 passes. Soudns about right? Does this vary with
how beefy one's lathe is?

Michael Koblic,
Campbell River, BC