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.

Quote Originally Posted by m_c View Post
Space is certainly a challenge with triac spindles.

Andy, what is wrong with your spindle motor/drive?
Mine started hesitating and making what's probably best described as a rumbling noise, followed by tripping the RCD at higher speeds. I took the brushes out, and there's signs of arcing on one of them, and another was sticking in the holder, but giving them a clean never made any difference.
The armature isn't that clean looking, however I won't be able to get the motor apart without using heat to get the pulley of, and I suspect the real problem lies with the drive. For it to trip the RCD, there's either got to be an excess build up of carbon inside to give continuity between the brushes and the case, or the SCRs on the drive are starting to breakdown and shorting to GND.
From past experience with my old lathe, the rumbling noise is consistent with a faulty drive.

If you want a new replacement DC drive, KB Electronics drives aren't that expensive. For basic speed control, a KBIC would work, or if you want to keep the tacho feedback, a KBMM would be needed. You'd also need to add the extra heatsink for either option to get the rated power capacity.
Axis Controls are one of the UK distributors, who I'd happily recommend as they've always been helpful when I've used them - http://www.axiscontrols.co.uk/shop/kb-electronics-dc

I think I'll go and start a new thread about my replacement plans, as I'm umming and arring over the design.