Denford Triac VMC with ATC Conversion / Fix

[m_c]

bit of a thread hijack sorry.

so when I got the machine it turned on and worked, but every time I started the spindle it tripped the RCD. I notice straight away the main fuse on the sprint drive card had been bridged, so assuming it was a known problem.

after many hours of faffing I took the top cover off the sem motor and it was filled with burnt carbon from the brushes. after a really really good clean and hoover, it worked and didn't trip the rcd.

I also replaced the brushes in the side of the sem motor just for piece of mind.

a problem since I had the machine is you start the spindle at say 3000rpm and it starts to jump around going up and down, by like 300-400rpm. so sent it away for a £500 refurb and it hasn't fixed the problem just changed the problem. now days when I set the motor to 3200rpm, it will go to that speed then after about 10 seconds jumps to 3800 where it will just sit until turned off. its not a big deal I have live spindle feed back so I can account for it, but it shouldn't be doing it.

That does sound more like a tacho or drive fault. Have you tried monitoring the tacho voltage, to see what it does when the speed changes?
If the tacho voltage is increasing with the motor speed, then it's most likely a drive fault, but if it drops first, then there's a tacho problem.

[andy_con]

I haven't no, you could spend more time trying to fix these machines than machining

That does sound more like a tacho or drive fault. Have you tried monitoring the tacho voltage, to see what it does when the speed changes?
If the tacho voltage is increasing with the motor speed, then it's most likely a drive fault, but if it drops first, then there's a tacho problem.