[MikeC8]

Being these machines do not have spindle encoders, it would probably be a good idea to use a RPM gauge with out a load, adjust the program, then run it on a scrap piece while tapping a hole and watch the RPM's, adjust again if needed.

I have a RF45, but they have simliar quirks of a Tormach. I find that my machines RPM will vary across the board. One of these days I should make a chart, mapping the input RPM vs actual RPM.

[shred]

I have found that measuring with a cheapy optical tach and bit of reflective tape on the spindle, that the RPM varies 10-20 RPM from the same commanded value even without load. I can't say if that's the tach or the spindle control, but something to think about.

Of course +/-10 RPM when tapping say a 32 TPI hole 1/2" deep at 500 RPM will end up being pretty minimal anyway.

[SCzEngrgGroup]

The magnitude, and direction, of spindle speed error can vary greatly from one machine to the next. The most common means of speed control is an analog control voltage, generated by a PWM-to voltage circuit or a Step-Pulse to voltage circuit, both of which typical have significant non-linearities. For some, those non-linearities are quite significant. The other, less common but better, means used in some VFD-driven spindles is direct RS-485 communications with the VFD, which will typically be more accurate, but can still be off by as much as 5%, especially at very low speeds.

Again, even a 10% error is no problem at all when tapping with the (more common) Chinese or Tapmatic heads. The Chinese head I have has enough over-travel to tolerate the spindle running as much as 30% slow. It is only the (relatively less common) Procunier that is sensitive, and then only to a slow spindle. A fast spindle will work just fine with all three. So, anyone NOT using a Procunier can safely assume the actual speed is equal to the commanded speed, and is unlikely to ever have a problem. I can't think of any other condition (apart from rigid tapping which few hobby machines do) where having precise spindle speed is at all necessary.

Regards,
Ray L.

[BAMCNC.COM]

Tomorrow at 10AM Ray owes me a beer

[tmarks11]

Tomorrow at 10AM Ray owes me a beer

What, new video on tapping coming out on your channel? Going to break a few taps as a demonstration?

[SCzEngrgGroup]

Tomorrow at 10AM Ray owes me a beer

Your PM box is full....

[BAMCNC.COM]

You were right Tmarks.. the greatest post of all time... vanished. I'll step out of this thread now...