"Robin S." wrote in message
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Does anyone else do it this way? The instructor who taught me is a very
knowledgeable German-educated millwright (different meaning in Germany,
apparently) and the first time I tried it I had far more success than
using
the old 29º method.

That is nothing new, but I don't endorse it unless you are cutting multiple
entry threads on an item chucked instead of running between centers, or
you're cutting threads other than 60° form. It is especially effective on
Acme or square threads. The real problem with that method is if you're
cutting (60°) threads that will get inspected by a comparator, and I've been
there, done that, many times, the form will likely be out of tolerance so
you risk making scrap, even though rings or a snap gage may say the thread
is acceptable. The flat on thread forms has a tight enough tolerance that
the side motion necessary to clean up the threads risks cutting the flat too
wide. Threading with a sharp pointed tool is not a solution, for that is
also a scrap thread.

The second problem with that threading method is chip flow and tool tip
loading, generally leading to tip failure. If you're threading at high
speeds using carbide, the problem may be lessened, even insignificant, but
that threading method otherwise is generally a recipe for tool failure.
CNC threading at high speeds seems to work fine when so fed, something many
guys do because they don't want to pay for the feature that permits "proper"
threading. I imagine the chip flow characteristics are much improved by
running the cut at the "sweet spot", but I have nothing to document my
opinion.

My threading practice has always been to feed at 29°, but to take the final
few passes by plunging with the cross slide, but taking light cuts, no
greater than a couple thou, and as low as a half thou when going for a fine
finish. Requires a sharp tool, but your suggested method does, too. The
advantage of finishing by my method is to eliminate the chance of ruining
thread form by widening the flat.

Harold