Changed carbon brushes cs70, now SPARKING

[Ruben Phrisius]

Hi guys, can't find any info about this on the web.

I just changed the carbon brushes in my cs70 and now the machine sort of stutters when I turn it on. The blade is turning but the motor accelerates and decelerates constantly. It sounds like a kid trying out his new dirt bike. It's like the rotor touches the brushes and then it doesn't and then it does. Like the springs holding the brushes in place are not tight enough, but they are, I checked

I called festool and they didn't know without seeing it.

Now here is a thing, only when I changed the brushes and put everything back in, I found out there is a handy little hatch for changing the brushes. So what I did initially, is take the whole motor apart. I was very careful with the rotor but maybe I scratched something, or some tiny piece of dirt got on it? Could that be the problem?

[EDIT] Today I checked the brushes while the motor was running and a lot of sparks are coming off. I am afraid this could mean anything from the motor being damaged to the brushes "bedding in".

I don't really feel like sending the machine to festool, but maybe I have to...

Any ideas?
Thanks in advance!

 

[Brice Burrell]

I've had this happen on a table saw once before.  In that case the area where the brushes go needed cleaned and that solved the problem.  In your case I'd try letting the saw run for some time to see if that fixes it, it may be the brushes need to seat.

 

[Ruben Phrisius]

Thanks for replying.

Well I took the motor apart again, very carefully, and made sure that the rotor was clean. Then I put everything back together again and it seemed to work.

Now after cutting some wood for like one minute it started doing it again.

So my theory is that I somehow changed a micrometer in the position of the rotor and it is not turning completely free anymore. I am afraid that I might have to send it to Festool.

Anyone of you have any idea how much something like that costs at Festool? And will they fix only that, or fix every little screw and when there's a little crack somewhere, replace that entire unit?

 

[AlexThePalex]

When you send it to them they'll only fix what you have indicated as the problem. So no, they won't look at every screw and little crack.

But with labour at 45 to 60 euro per hour, and the size of the CS 70, I guess you might expect at least 150-250 euros for total cost. If there's something with the rotor or the electronics, it can even be a lot more.

Best thing to get to know their procedure is to call them and ask them. I think you can send it in, pay a basic fee for inspection and get a quote for a full repair.

But there's a big chance the problem is only the new brushes that need to be seated. Just use the machine and let it run. Might take a couple of hours though.

 

[Ruben Phrisius]

When I called them, Festool said new brushes should work instantly.

Thanks for the cost indication!

 

[Ruben Phrisius]

Looking in the motor while it's on, I can also see some worrying sparks coming off the brushes...