Why are threads cut at slow speed?

[Dr Stan]

For threading on manual machines I usually limit myself to 150 RPM or less.  Way too slow as to recommended cutting speed, but you got to be able to react fast enough to avoid wrecks.  The spindle speed is also highly dependent on the pitch of the thread.  Coarser = slower.  Finer = faster.

Before NC & CNC lathes high speed threading attachments were available for many lathes.  Once set up they would disengage the half nuts and back off the cross slide at the end of the thread.