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I have a 3 axix CNC converted Conquest mill (from Chester UK) controlled by Mach3/Geckodrive G540 and recently got quite happy to make it work with the VFD (RPM controlled by Mach3).

For that I simply disconnected the potentiometer from the mill speed control  and replaced it by an analog optocoupler and a resistor. I know G540  VFD is already isolated, but the mill circuit board was powering the low voltage electronics directly from the 220V using a voltage divider... so it got me scared to simply plug the G540 directly.

The advantage of this approach is that I got a working VFD almost for free. The disavantage is that it is highly non-linear. The spindle only starts to turn at about 30 RPM when I command 400 RPM, it  gets close to the commanded value at about a 1000RPM then it undershoots.

So I thought "Lets use the Mach3 spindle calibration and it will work fine"... Well, wrong... for some reason the calibration, at least in my version of Mach3 would not work. Probably it works for correcting small deviations but for my cheapo VFD it was hopeless...

So I read some threads here about this problem and it seems somewhat usual. People referred to a file named "Linearity.dat" so I could not resist taking a look at it.

Long story short, the linearization strategy implemented in Mach3 is actually works great. The problem seems to be the function that generates the file, it probably does not assume that a VFD could be as bad as mine  :D.

So I wrote an Excel table that takes as input the commanded RPM vc Real RPM and produces a  "Linearity.dat" file that works fine.

I am attaching the Excel file so that you guys can try it out. Can´t guarantee anything but that it worked for me. But if some of you have the same issue, I hope it helps.

The way it works is the following:

1- Only make changes to the GREEN cells.
2- Enter your min and max RPM. It will generate a list with 101 input values for you to fill.
3- For each entry, command your machine to spin at the COMMANDED column (blue), take note of the real RPM it is spinning and enter it in the MEASURED column (green)
4- Click the CREATE FILE button. It will run a macro that writes a linearization file. That is the  "Linearity.dat" file that Mach3 is able to read.
5- Shut down Mach3 and copy that file as to replace the one you have. In my case it happens to be at "C:\Mach3\macros\Mill_RS".
6- Start Mach3 and try to see if the RPM is correct now.

Hope it helps.


General Mach Discussion / Spindle Speed never shows RPM, can´t figure why
« on: November 16, 2015, 04:40:15 PM »
I have set up the Index signal from a parallel port input and it toggles correctly as seen in the Diagnostics window.

But no matter what , RPM values are never displayed in the Spindle Speed window. I even tried emulating with hot-key but although the input shoes the pulses, Mach3 seems to ignore it for reasons I can´t understand.

Hope someone can help me on this, I send attached the xml file.



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