Full speed as defined in the pulley ratios tab by the maximum RPM outputs a 10V signal and half speed represents a 5V signal. Likewise, when 5V goes into the VFD I'm getting 30hz out, 10V  = 60hz. The pisser is that the motor isn't connected to the spindle w/ a 1:1 gear ratio. This is why I originally thought setting the pulley ratio would be ok, but that effects the index pulse ratio and thus throws off my IPR calculation. Brian obviously acknowledged this issue since there is the auto spindle calibration function.

The calibration would be long before Brians time, would have been Art.
Remember Art posting something about deleting the linearity.dat and starting again but not really sure on the specifics as I didnt really pay attention.
Did you try messing with the speed in spindle pulleys but leaving the ratio alone?
Hood

I did. The minimum and maximum seem to define the 0-10V relationship with the S word in the Gcode and within the screen input DRO. Beyond that they don't have any effect.

What is the ratio for spindle to motor?
Hood

 I'm not sure exactly but it seems to be about 1.5:1 or so. The timing index to spindle is 1:1 and I have confirmed that only 1:1 should be entered in the pulley ratio box.

Yes the pulley ratio iis for the index so you need to leave at 1 if your index is not on the motor. If it had been on the motor then you would enter a ratio in that case.
I helped a friend set up his Avon lathe a while back, it was using a CSMIO controller which outputs 0-10v for the spindle. What we did was settle on what the top speed he wanted, 2000rpm. We then set that in spindle pulleys and then commanded S2000 and read what the spindle was actually doing. We then worked out the rough ratio of true to commanded and altered the Max Hz in the VFD to achieve the correct spindle speed, seems to work well.

Hood

 That was the route I was going to try tonight. 2000 RPM is my desired maximum spindle speed within Mach and is what I have for a maximum speed in the pulley dialogue. S2000 gives me 10V out, so I think your method of tweaking the maximum Hz output in the VFD to make a true 2000 RPM @ the spindle is a good premise. I now have these auto tune parameters driving a strange adjustment curve which could cause issues. You mentioned the linearity.dat file....if I find that and delete it should I be back to a linear curve in my PWM output?

Yes you will need to delete the linearity.cat, you should find it in the macro folder of the profile you are using.
Hood

ual;l; I got the spindle close enough to be called "good for now". Changes to the spindle motor tuning in terms of steps/rev, max velocity and acceleration have 0 effect on the PWM pulse as best I could tell. I ended up setting steps/unit to 60 and then maxing everything else. With my particular VFD (Durapulse) there was a series of analog gain settings which define a linear relationship between control voltage in and the resulting motor frequency output in Hz. Once I got this dialed in to my particular settings I used the spindle autotune calibration routine within Mach to tune the actual voltage output from the C32 to the VFD to provide as linear a response as possible. I really like the concept of the auto tune, and even the initial autotune sequence. What I don't like is that I can't manually adjust particular control points after the control offsets have been established. What would be awesome (Brian and Mach4....are you listening?? ) is if you could interact with the resultant offset graph after the initial tuning run my just pulling on control points with the mouse. The control voltage output from my system is not linear so a modifier every 10rpm or so is necessary to keep the resultant voltage linear. It would also be cool if you could define the delta between each control point, so if you needed finer control you could have control points every 5 RPM while somebody who doesn't need it that precise could have control points every 50 rpm.

Anyway, for the most part when I key in an RPM, it gets to within 20rpm of the setting which is good enough for now. The only blip I still get is between 1700-1850. If I key in 1650 the rpm goes to 1650. If I key in 1700 the rpm goes to 1820. 1840 gets me 1890, and then 1900 gets me 1930. 2000 gets me 2000. Up to 1650 I get within 20 or so of the set rpm. If I could have access to the control points I could manually modify the particular range of interest, or better yet, have the auto tune actually get the curve right

That might be asking too much.

Ah ok thought you previously said the output was linear.
As long as you have it sorted now thats all that matters
Regarding Ver4, it likely will be done, maybe not at first but the modular way Mach Rev4 will be done it will make adding things easier and they wont  break other things.
Hood