Motor or controller issues older SX3 mill

I have a SX3 mill that is getting on a bit now, it is on its second dc brushed motor that gets through brushes quite quickly. It sparks a lot intermittently (around the brushes I think) and quite often will not start until it is run backwards a rev or two, After which it will start forwards. It will occasionally just stop. It will restart again at low speed but doesn't like higher speeds any more.

I can get a motor from China (I think I bought the last one in the Uk 4-5 years ago) but it isn't cheap, is this likely to be the motor or could the controller be causing the issues? I can't get a controller and I'd rather not spend many beer tokens on a motor if the controller could be the issue.

Any advice gratefully received.

Try cleaning the commutator with some fine abrasive on the copper and use a fine hook to clean out muck from between the commutator segments. Worked for me on the Bridgeport power feed DC motor.

Andrew

Thanks Andrew, I've sort of tried that by using a fibreglass scratch brush as I can't access the commutator very easily. It might have made it better for a few days but that also might have been wishful thinking. I'll have a look this morning and see if I can take it apart and have a better go.

the sparking will be eroding the brushes quicker and making the commutator dirty leading to more sparking. Make sure the brushes move freely in their holders and the springs are not snagged on the holder so they don't push firmly.

I have taken the motor apart this morning and cleaned the commutator. The live crimp connector to the brush holder was corroded and not particularly tight so that has had a seeing to as well. At some point in the past the brushes have worn or burnt away completely which has resulted in some damage to the commutator. Some of the fingers have almost fused over the gaps from heat damage so I've made sure none are touching their neighbours. On putting it back together it is running significantly better, no hunting, starts first time and no sparking!

Thank you both for your advice.

I've had pretty much the same issues with my Warco WM-16 for a long time. The brushes in these motors are incredibly soft when compared to other DC motor brushes, like those used in power tools.

I reshaped my brushes by very carefully running the contact face along the curved edge of a half round file, similar to the radius of the commutator. It does work but the bushes soon wear down again. I also think the controller is prone to poor speed regulation, adding to the frustration.

The experience I've had with DC motors in power tools is that, if the commutator starts to flash then the armature is on its way out, however I'd never claim to be a motor expert.

I had considered sourcing brushes with a harder compound, but I've now gone ahead and bought a new 3-phase motor and inverter, hopefully to be installed soon.

Ed.

If the commutator is no longer round, the problem may not be solved completely at higher speeds. If the brushes are not in contact with the commutator all the time, arcing may occur, brush wear will increase, etc, etc. Cutting the commutator back to round, and under-cutting the insulation between segments, is the cure. Likely only possible once or twice on cheap modern motors.🙂