I have an older CNC Mitsubishi ram EDM (M25) with a tool changer and I want to start converting it into a small automated CMM.
My goal is three tenths to half a thousandth accuracy. The mits motors/table are accurate to about 50 millionths, so if I can keep the setup rigid and the software under control, I should be able to get there without using air bearings. I'm good at software and systems integration. I am at the stage where I am trying to block out how the system would work.
It seems the Mach3 card would be able to control the stepper motor output (I believe they are steppers) and tell me when the probe fires. I guess I would need new chopper drives for the motors, since the present ones are in the cabinet and I no longer need to draw 40 amps of power.
My idea is this:
1. Dedicate a PC to run this thing.
2. Program the probe movements using G-codes
3. Have a Mach3 (or other board) control movement and acquisition.
4. Pull the points in, write some simple routines (to start) in C++ to get center and radius for arcs and circles, slope and intercept for lines, intersection points, etc. ( unless there is stuff out there to do this inexpensively - and I seem to remember there was but I lost the file on it that I put together last year).
5. Do the same type of routine to translate CAD output (DXF or CADL) for comparing the gathered data to mean print dimensions.
6. Send the data to a comparison routine (could be EXCEL to start) and into SPC output.
The key would be that while I was running the CNC Mills and Lathes (I own a machine shop), the CMM would be checking a part on its own. And the system would operate exactly the way I want.
Please help me with any information you feel like sharing.
Is there a low cost CMM-oriented board around like I remember?
What chopper drives would you recommend? (These are small motors, really only used for positioning. Optimally, I would want to control X, Y, Z and C, and trigger the tool changer to somehow load probes in different orientations. But in the beginning, I would just use one wired probe.)
What controller would you recommend? I need accuracy, as I did not find glass scales on this machine (though I have not yet started disassembly).
Any other pitfalls that I am overlooking?