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MRC 40 spindle motor has stopped


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We've got a problem, the motor will not run for the spindle.

It stopped during a job after cutting for 40mins through bolsa wood using a 6mm ball nose cutter. It ran fine then stopped, starting twice for a sec before stopping completely. All other motors and switches are still working.

The relay kicks in and there is an 230V ac output from the board. But the spindle motor is unresponsive.



Here are some things to try, but I'm guessing you may have ticked them off already...
  1. Check on / off switch on Kress motor has not tripped to the off position.
  2. Take the Kress motor out of the MRC 40 and plug directly in to 240v mains supply, will the motor power up.

Let me know the outcome please.

What next..... Carbon brushes need replacing or motor faulty. (Hope not!)

Roughly, how many hours do you think the motor has run?

We have emailed Kress in Germany to see if they have an agent in Dubai if the carbon brushes need replacing.

Also - I've taken the liberty of adding you to our contact DB and you will be receiving future F1 in Schools related announcements. Ok?

Another comment - 45 min cycle time for one side of a car is very long, usually 12-20 mins is normal...

I've had the motor out and checked the switch, which is locked in the on position. Then tried a mains straight to it and nothing.

I would say it's only had 35hr run time of which the maximum single cycle has been 45min.

I'm a little cautious of opening up the motor in case it voids the warranty. The spindle is free to move and there is no grating sound which makes me think it might just be a dry solder or lose wire.


I wasn't cutting a car at the time. It was after an area clearance with 5 mm step down and the feedrate nothing more than it should be able to cut in balsa (it wasn't struggling).

Thank you for your swift reply.

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We need to inspect the carbon brushes for the spindle motor. It is normal for these brushes to wear over time and need replacing. I'm not sure of how many hours of operation is expected before replacement is normally due.

The PDF below provides a complete schematic for two Kress motor models. I'm not sure which one you have. Dissassembly from the top of the unit to reach the carbon brushes should be relatively straight forward, but we recommend that you only proceed if you or one of your schools technicians is confident in being able to perform this without damaging any components. (You will see the carbon brush part numbers listed in the legend with the schematic.)

During dissassembly you should be able to inspect the ability of the brush wear state and relative ability to contact the armateur.

Kress parts and diagram.pdf

Once you have the brushes removed please upload a photograph and supply your comments / findings.

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Cheers for the help,

I had the motor apart and found there was very little ware on the bushes.

After building it back up it started running fine again.

My guess is the switch extentsion arm had come off inside the housing.

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