I would imagine it would error if not correct.
Only thing with a VFD is you may travel slightly further than the commanded depth.

Well thats good news...

Seems to work just fine with the M84 macro

Tried various pitch and depths all the way up to 5mm pitch which is a bit steep

Couple of notes though - it needs a good headroom on Z above the start point as it overruns on the withdraw and will trip the soft limit again. Also at 300rpm it will overrun the reverse point by about 3mm on a 1.5mm pitch, just need to be aware of that

A little video...
https://youtu.be/ttz_LNAEEdA

It certainly tracks the rpm as i was gently applying the spindle brake while it was doing its thing and you can clearly see the Z drive belt changing speed with spindle speed

Also, the new DRO39 now shows real rpm - nice.

I played with the Mach pid loop again and although it did stabilise the speed at exactly the requested speed, it took a while to do so, i'll leave that off i think.

So, what sort of tap holder do i need to look for - floating, fully rigid??

ER collet holder does fine for rigid tapping, no need for a floating.

No overrun with a servo spindle or even if you could utilise +/-10v with a VFD and tune via the plugins PID. With the open loop VFD then you will get the overrun.

Hood

Pretty certain the vfd only supports 0-10v plus fwd/rev signals and not +/-10v so cant use the CSMIO servo DAC output or pid.

Not to worry, i think it will do fine, just need to assess the overrun before diving into a job and make allowance.

Just call it short, run it and see how deep it goes then alter the depth and run again if it wasn't deep enough.

Was recently asked for some videos, here we go...

Rigid tapping...
https://youtu.be/1UOak0qTHsY

Full machine conversion walk-around...
https://youtu.be/utjrP_94KIk

Looks to be working well
I can see all spare pieces of metal in your workshop will soon have tapped holes in them


Hood

LOL

Already found a use for a bunch of aluminium offcuts - the support bracket to hold the auxiliary spindle when not in use. Will be mounted up where the lifting eye goes on the top of the ram.

Designing it now in fusion - loads of tapped holes, chamfers, multiple tool changes, facing, boring, counter-boring the works

Here we go, nice fun little project for a Sunday morning....

Fits perfectly, works well and used loads of tool changes

Nice