Oh and make sure you use the Index input if using a single slot disc.
Hood

can you give me a target discrepancy to aim for between actual and commanded spindle speed please!,  whats the general results people have, should it be a stable speed reading? few rpm, or better still none at-all with no load!?

My Bridgeport mill just has manual speed control, was going to hook it up to Mach at some point but once I get the Beaver Mill finished I will probably sell the Bridgeport so I am not going to bother at this time.
 On the lathe the speed is controlled via clutches in the gearbox and Mach switches between the clutches over ModBUS so really maybe these are not good examples for you in as much as the actual speed control, however both read exactly what they are supposed to and if anything  the reading fluctuates by 1 RPM. I dont have spindle speed averaging checked so I know that is a true reading.
Hood

im aiming for nuts then i guess, big target!. if anyone had confirmation of electronic rpm fluctuation for the dro on a set machine i would be obliged, i've just turned mach on so im looking for a standard to work from.

 I appreciate what you say about the mechanical machine is driving the dro.  Tell me you have a modbus controlling different clutches inside the gearbox, thats pretty smart, i did not know a cnc could effectively change gears!, i have hope for a machine with torque yet then! was it a conventional mahcine or a cnc to start with?

The Lathe was set up that way from the factory, it has a gearbox with 5 electromagnetic clutches which can ne engaged in a few different combination and this give me various spindle speeds. I am however planning on fitting a big AC servo I have instead of this arrangement, that will give me infinitely variable speed up to the 2000RPM that it runs at now. I just hope the motor will be big enough, its slightly bigger than the motor thats on now being 12.5KW(11KW now) but will have to wait and see what it is like when connected. I hope to be able to hook up to the gearbox for testing and if its not quite powerfull enough then I will use maybe two of the ranges of the gearbox. If it is powerfull enough then I will do away with the gearbox and direct drive to the top gearbox that has a manually controlled High and Low range.
Hood

5 emc's, very interested to see that box.  
 did you remain with the origonal motor frame size?.   I just managed to squeeze the next up into the space giving me a massive power increase of 180w  (0.55Kw from origonal 0.37) .   still, the inverter will give a programmed torque boost of another 50%, the top end was sacrificed for 1.1:1 pulley reduction to give some more gain at the epxense of some top end.




I took out the index plate and turned that down to get rid of the 100 slots,  milled in a 10mm square, now it works  better for pick up, it still fluctuates around 10rpm quickly in the dro. after calibrating further 2490 = 2490 actual,  and 1000 = 1010 actual, and  600 = 605 actual. so its close!

but there is still some discrepancy at the very low speeds / 200=305 actual or so.  for some, and it may be my oversight and inexperience, mach has difficulty calibrating/syncing the low speeds in for step tuned spindle motor?.  I'll give it another go. thanks for the help so far its working out well

Try increasing the index debounce a bit and see if that helps, wouldnt put it too high though. Never set up VFD control so I dont really know anything about it. I think JimPinder has so might be worth giving him a shout.

Dont have any pics of the box I am afraid, the manual has some line drawings of it, if you are interested PM me your email and I will send the manual (2megs approx). I still have the original AC Induction motor on it (11kw) and not sure what the frame size or even the shaft size is. The new motor has a 42mm shaft but it would be too good to be true if that was the original motors size 
Hood

i have now tried changing the p.i.d values, it seems to hunt about too much like that, i checked closed loop feedback that also takes too long to settle, although it hunted out the commanded value for once!.  Averaging is more like pulling the wool over your eyes..!   

Im on 45khz , have one slot in my index pulse plate 10mm wide on a 94mm diamater plate.   On my inverter 10V = top speed @ 50hz = 2790, through 1.1:1 pulley = 2536.   Ive calibrated the spindle in at 1-2-3-4-5-6 ~ us.
 i can get good results for commanded in the mid to high range 750-2500,  within target to 5-8 rpm, (thats adeqaute for sure on a low inertia pint sized drive)   but for some reason still in the lower rev range when calibrating mach just dosent pick up the index pulse properly below 750. it can be anything upto 100rpm out, its non linear also,  just to be even more of a figure out!.


when initiating auto-calibration it starts the spindle around 125rpm,    and my motor spins at around 44,
mach has to increase to around 250 before the spindle starts to register steady speed at around 75-100rpm, before that its not registering properly in mach. 

by the time it gets to around 750rpm the spindle speed actual has caught up with mach calibration commanded, and from then on upto 2500 its better.  why when mach is calibrating does it not wait for the actual speed to catch up with the commanded before the commanded moves onto the next reference point up the graph* etc!.   perhaps its an acceleration thing, i'll try that next. 

i increased the acceleration rate on the vfd side,  by around double, and also the acceleration in motor tuning to nearer top end.    it seems to have further improved the accuracy of the spindle calibration and the dro.  I'm to within 5rpm open loop now all the way through  from 500-2490 rpm, does it get much better on a light weight drive? . 

at s500/400/300 it jumps plus to around 40rpm out.  funny thing is , when i command 100rpm, it jumps right upto top speed, perhaps someone can pick up on that issue.

I shall continue testing!.  I notice alot of others have had similar experience by doing a search on spindle calibration.  I wonder if its the board im using to convert step to volts if its a linear increase at the bottom end.