On Apr 22, 2:04*am, "Ed Huntress" wrote:
When you cut threads by feeding straight in, you're cutting both flanks of
the thread at once. That produces twice the tool load for a given depth of
cut.

If you have a good lathe, your tools are sharp, and you're cutting aluminum,
it may work just fine. But cutting clean internal threads depends on getting
things pretty close to right, so the extra tool load is something to watch
out for if you get some chatter.

--
Ed Huntress

Of more importance is that cutting on one flank loads the cutter
against the lead screw. Cutting both flanks at once, the carriage can
float instead on being driven by the leadscrew, and you can end up
with a drunken thread.

John Martin