I have a mid-2000s Dremel 400XPR that I've used over the years for a variety of projects. A couple days ago I tried to use it and found that it doesn't power on. I read through the manual, tried a few different (working) outlets but still nothing.

Is it worth replacing the carbon brushes or is that unlikely to fix it?

Photos at: https://imgur.com/a/qpqKOj4

  • It's certainly worth inspecting the carbon brushes. Does the mandrel spin freely? Oct 22 '19 at 16:29
  • I took them out but don't really know what to look for. My fingers were black after touching them. I will see how the mandrel spins when I get back home from work tonight.
    – Dan K
    Oct 22 '19 at 16:56
  • Pop us some photos of the brushes if you can. Be careful of orientation putting them back in; at least have the curve go the correct way, and at best have them oriented the same. Oct 22 '19 at 17:32
  • OK, I'll post some photos tonight.
    – Dan K
    Oct 22 '19 at 17:59
  • Posted the photos!
    – Dan K
    Oct 23 '19 at 20:23

My experience is that the brushes sometimes become stuck in their channels so that they no longer contact the commutator.

  • Remove the brushes (if the spring pops off, pull gently with tweezers).
  • Clean the channel with a cotton swab.
  • Put a single drop of lubricant on the brushes.
  • Reinsert, keeping the curve of the brush so it conforms to the curve of the armature.

That often fixes the issue until the brushes are worn down.

  • Sounds like good advice. You would have to use your Dremel an exceptional amount to wear down the brushes. Inspect and reinstall first and you should see any obvious issues that would call for a brush replacement.
    – JPhi1618
    Oct 22 '19 at 16:03
  • @JPhi1618 I could easily see brushes becoming frozen in their tracks to where they no longer sink as they wear. At that point, a gap would be created, and current would arc across the gap for a time, spalling both the brush and armature until this stopped working. It might be quite damaged at that point. Oct 22 '19 at 16:31
  • Thanks for your reply. I don't know where the spring is. I took off the plastic brush covers and pulled the brushes out after disconnecting the metal connector. What part of the brushes should be lubricated?
    – Dan K
    Oct 22 '19 at 16:58
  • On some Dremel tools, there's a small brass spring that pushes the brushes against the armature. If not, no problem. See illustration at homedepot.com/p/… . As for oil, it's optional... one drop along the side of the brush can help, but too much causes arcing. Oct 22 '19 at 20:38
  • I tried this last night, minus the oil. The Dremel still doesn't run. Any other ideas?
    – Dan K
    Oct 23 '19 at 20:24

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