[mountaindew]

Doesn‘t your spindle speed DRO show the actual revs when running?
Step

Yes!
How accurate is it set from factory?
Never worried to much about this until RIGID tapping.

Mill has same PP dro and it required calibration to be even close.
Didn't you have to calibrate and set spindle speed when you set your mill up?

From the manual
Attachment 460588

[kstrauss]

Isn't the actual spindle RPM irrelevant with rigid tapping? The infeed/outfeed should be controlled by the spindle rotation.

[shred]

Isn't the actual spindle RPM irrelevant with rigid tapping? The infeed/outfeed should be controlled by the spindle rotation.

Within the usual speed/feed limits of course. I've not done rigid tapping on the SL15, but have done lots of external and internal threads which should be very similar code-wise. You put in a short air-cut in front of the part to get everything synced-up properly.

My guess is it starts moving the axis at the 'book' rate, then modifies feed based on spindle encoder inputs, so you need enough encoder pulses for it to settle down. IIRC there's a tooltip in the conversational threading screen for that lead-in sync distance that suggests how long to make it.

[TurboStep]

Yes!
How accurate is it set from factory?
Never worried to much about this until RIGID tapping.

Mill has same PP dro and it required calibration to be even close.
Didn't you have to calibrate and set spindle speed when you set your mill up?

I did, but then I mounted an encoder The encoder delivers the exact RPMs and this value is (at least on my modified mill) displayed on the DRO. You can consider the encoder derived RPM value to be "exact".
As Ken mentions the feed tracks the spindle speed (on a non servo system) so the exact spindle speed is not particularly important.

Within the usual speed/feed limits of course. I've not done rigid tapping on the SL15, but have done lots of external and internal threads which should be very similar code-wise. You put in a short air-cut in front of the part to get everything synced-up properly.

My guess is it starts moving the axis at the 'book' rate, then modifies feed based on spindle encoder inputs, so you need enough encoder pulses for it to settle down. IIRC there's a tooltip in the conversational threading screen for that lead-in sync distance that suggests how long to make it.

On these non servo systems the spindle speed is harder to control so it's allowed to run and the Z axis motion is synchronized with the spindle encoder. At the required depth the spindle decelerates and reverses while the Z continues to track the rotation.
If I had a lathe I'd certainly be rigid tapping.

I can imagine on a large mill/lathe a little travel in the tool holder might be advantageous because there will be very little flex in the system. On at least my 1100 it works fine with a rigid ER20 holder.
Step

[kstrauss]

Step, I believe that you have added rigid tapping to your 1100. Any chance for a few details of what is involved?

[TurboStep]

Step, I believe that you have added rigid tapping to your 1100. Any chance for a few details of what is involved?

I believe I did
Originally using a parallel port and later through the mesa card. There are a few issues if you want to avoid a custom Bit file and I wouldn't recommend my solution to anyone else. For milling I only thread mill so I haven't tried it for quite some time. I did notice that the RPM DRO no longer showed the speed when controlling the spindle via the potentiometer so I'll have to look into it some time. Things did change when Tormach introduced the encoders on the MX series so I expect I need to adapt somehow.
I'll let you know if I make any progress but I'm afraid it's not high on my priority list.
Step