Centroid Community CNC Support Forum

Making huge strides in my build. I have my spindle up and running, start, stop, fwd, rev and alarm all work. Speed changes in MDI make it spin faster and slower when changed. Problem is that the 24k RPM spindle speed (and VFD) are far too fast. S22000 maxes it out at 24000. S6000 is around 6800. Speeds are stable, so I don't think it is a noise issue. The 0-10v wires are in CAT8 double shielded cables, drained to ground. If it was wire resistance, the voltage would be lower, and this seems like the opposite problem.

I ran the bench test multiple times with different meters, all within a hundredth of a volt, so acorn output appear to be good. I suspect the VFD is simply misinterpreting the input.

I experimented with the 4 reference voltage values in the bench test program and can slightly improve the desired vs actual speeds, but at best 23000 requested spins 24000.

Set it all back to my true measured values, and experimented setting the max spindle speed in cnc12. I have it on 25250 now, and most speeds are within a couple hundred RPM, plus or minus. Many speeds are only 25-50 rpm off.

Is this an ok workaround? Will it cause any other issue? Anyone had this issue and solved it differently? Any other fix I should try? Thinking maybe inserting a trim pot in the 0-10v line, but if the kludge above is ok, less parts is a good thing.

That is the correct "workaround" to calibrate the spindle speed. Somewhere in the 25k range is usually around 24k. 25-50 rpm off is a great reading. Don't expect much better than that over the full range. 1% of 24K is 240 rpm and you are way under that if you are only off 25-50 rpm. Be happy with your settings.

A recent rebuild I did for a customer with a 18K spindle required me to set the max spindle speed in the wizard to 18,451 to get a solid 18K at his spindle.

If your speeds are stable great, if they fluctuate at all you can install a .1 mfd cap across the Acorn analog output.

ShawnM wrote: ↑Mon May 08, 2023 11:22 pm That is the correct "workaround" to calibrate the spindle speed.

Thanks for the quick confirmation. I had found mention of the capacitor, and may add it, though I only occasionally see it vary, and only by a tiny amount.

Fully agree with Shawn's recommendation of a 0.1 uF capacitor as this can correct even smallish errors in observed vs actual speed in addition to fluctuation as shown in my case below:

https://centroidcncforum.com/viewtopic. ... 225#p48225

For the record, I used a ceramic Cap which is polarized. If using the same, just ensure the correct polarity when connecting across Acorn's analog terminals

Ceramics are non-polarized caps and are the correct type to use. While the Acorn's DAC output is polarized, noise is not.

Quite right, just rechecked and my caps are definitely ceramic and not polarized.

I used to be forgetful, now I can't remember