My understanding is that you're never going to get a 100% correct voltage, but as you say, they are pretty close.
What this means, is that your Mach3 settings are correct, as The G540 is sending the correct voltage to the VFD.
The issue is that the VFD is not giving the correct speed that corresponds to the input voltage.

I've heard that better VFD's allow you to adjust this to compensate for voltage irregularities, but I don't know if yours does.

I understand what you are saying Gerry but as I explain below the VFD produces the 400Hz / 24000RPM and varies the speed with the local contro so to my opinion I’m missing a setting somewhere and perhaps this setting is on the VFD.

I first verified that the VFD on local control takes the spindle to 400Hz and it shows RPM=24000. Then changing the VFD to external control (Mach3) and asking for different speeds with different pulley speeds and ratio I don’t get what I want (BTW I deleted the “Liniarity.dat” from the Mach3 Macros folder as I read this file should be deleted and Mach3 will regenerate it)

Pulley min / max 0/24000 ration 1:1
S6000, VFD shows 11299RPM / 186Hz, G540 volts 2.42vdc
S12000, 15398RPM / 256Hz, 4.81vdc

Pulley min max 0/30000 ratio 1:1
S6000, 10492RPM / 174Hz, 1.95vdc
S12000, 13752RPM / 299Hz, 3.85vdc

Changing the pulley ratio to 0.80 does not change the above.

In other words I’m running out of options on how to calibrate the spindle to be “close” to what I’m asking. I will investigate if I’m missing a VFD parameter

BTW Gerry I think the VFD only outputs 10vdc (9.89 in my case) and it’s up to G540 to interpolate this voltage and output the correct volts to Mach3. Am I correct?

Pin 7,8,9 of the G540 connect to 7 - ACM: 8 - V1: 9 - +10.
The 10v is used by the G540 to power the analogue output of the G540.
And outputs on term 8.
Nosmo

Thats correct Nosmo, my wiring is the same

In other words I’m running out of options on how to calibrate the spindle to be “close” to what I’m asking. I will investigate if I’m missing a VFD parameter

Try going to Function configs and then open the spindle calibration tool. It should allow you to get closer.

No idea how to go to Function Config and the manual i have says nothing about it. Can you explain how?

On the Mach3 main screen at the bottom right there is the “Spindle Speed” controls. Under the Reset button there is the RPM box. Why I don’t see a value there when my spindle runs?

I only see the RPM at the bottom in the Spindle Speed box

At the top left of the Mach3 screen it says file, then Config, then Function Config's. click on function Config's. The first option is calibrate spindle.


HTH

Mike

I thought spindle calibrate only had an effect if there was encoder feedback of the actual spindle speed i.e Mach3 was controlling the Pid loop???