Introduction: Dremel Repair

About: Professional work in various electrical and mechanical fields, obscure sense of humour and typically willing to help... Currently under contract designing environmental monitoring equipment.

So my Dremel 395 died mid project!

No power no strange noises! it was just mocking me and acting like it was unplugged!

I figured that since it didn't smell of burning metal I should be able to get it going again.

Step 1: Assess the Mess!

I did notice that it was running hot for the past little while.

First unplug the tool.

Check to see if the shaft spins freely, if not you may have a bearing problem. You can sometimes free up a bad bearing with light oil but noisy bearings mean mechanical damage and it should be replaced as soon as possible. If the bearings are bad then the whole armature will need to be replaced. this is available online for around $17.

If it does then next check the brushes. These are under small blue screw caps on my tool. They should remove easily and have lots of carbon "brick" left.

On my tool one came out easily while the other separated from the spring and remained in the brush holder.

So it looks like I have a stuck brush which has worn down and no longer makes contact with the commutator (more later)! This explains the no power situation!

Step 2: Disassembly

Remove the hanging clip

Remove the body screws, mine were torx 15

Gently separate the body halves making sure that no small parts fall out, like the shaft lock assembly at the nose of the tool.

Remove the motor assembly from the body making sure to note which side is up with respect to your dis-assembly order.

Remove the rubber spacer at the rear of the motor shaft

Gently pull the brush block assembly rearward to remove it.

Step 3: Repairs

Use a rounded tool like a screwdriver shaft and gently push the stuck brush out of the brush block.

Check for damage, in this case there was none and I was able to re-use the brushes and brush block. Gently dress any warped or melted plastic with a needle file or sand paper.

Reattach the spring to the brush using mild force.

Test for proper fit by inserting the brush to make sure that it doesn't bind.

I suspect that the heat was caused by a dirty and worn commutator ( where the brushes contact the rotor), which in turn caused the brush to melt into the carrier.

Using a very fine sand paper ( 800 grit) clean and dress the commutator until it is shiny and smooth. Clean the black lines between the segments of the commutator using a brass brush to remove any chance of shorting.

Step 4: Reassembly Notes

The brushes go in last! Severely worn brushes should be replaced!

The brush holder connects to the motor assembly via friction fit contacts. Gently press them into place.

Reattach the rubber spacer to the rear bearing and place the motor into the housing.

Place the other half of the housing in place and test that to motor freely spins, if it grinds, open the case and flip the magnet assembly of the motor over and re-install, it should be smooth now.

Screw the case shut.

Look for a dark line on one edge of the brushes, if there is one, then this installs in the direction of the arrow. Dark line in the direction of travel. Install the brush caps.

Plug in the tool and test. If it doesn't spin at this point then you most likely have a burned out switch, unfortunately that will need to be replaced. The switch is available online for around $16.

Mine now works better than it has in a very long time!

Now back to the original project...

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