RogerN wrote:
I'm not sure if it's practical but you could use a thread mill and a helical
interpolation. Thread mills might be too expensive but it's interesting
anyway!

Multi-row thread mills are REALLY expensive, well over $100 each, and
they only do a single thread pitch. Single-row thread mills can do a
wide range of pitches, and work like some kind of magic, but they are
slow. If you needed to do something like camera threads on the mill,
they'd be great.

But, a CNC mill and a tapping head works quite well, without fancy
spindle sync or precise spindle speed control. The CNC control feeds
the tap into the work at approximately the right feed to match the
approximate spindle speed divided by the thread pitch. Feed a little
slower to let the clutches in the tapping head adjust the rotation. The
CNC control handles the feed depth. When it backs out, the tapping head
reverses the spindle to pull the tap out. If these things work with a
drill press, they can definitely work on a CNC mill.

I have tapped thousands of holes with a Procunier "CNC" model 15000
tapping head. Any tapping head for manual drill-press use should work.
I also did a lot of work using combined drill-taps with the Procunier.
I have just retired it as I figured out how to do rigid tapping on my
CNC Bridgeport.

Jon