Dumore Hand Grinder Don't do Nothing

[Chips O'Toole]

I don't know if this counts as a grinder question, but here goes. I have a Dumore hand grinder. It's like a giant Dremel that runs at 25000 RPM. I got it in nearly-new condition, so it's not worn.

When I hit the "on" switch, it doesn't start. Then if I spin it manually, it takes off, but it doesn't reach top speed. The brushes look fine. What's going on with this thing? Are there tiny capacitors in there I need to replace, or what?

 

[woodchucker]

I don't know if this counts as a grinder question, but here goes. I have a Dumore hand grinder. It's like a giant Dremel that runs at 25000 RPM. I got it in nearly-new condition, so it's not worn.

When I hit the "on" switch, it doesn't start. Then if I spin it manually, it takes off, but it doesn't reach top speed. The brushes look fine. What's going on with this thing? Are there tiny capacitors in there I need to replace, or what?

it's a universal motor so no caps, if there were it would be for noise suppresion.
Take the motor apart and clean the commutator with an eraser. it should clean up the commutator.
Take a file to the brushes and clean up the ends.

 

[aliva]

Also check any bearings or bushings

 

[Dave Smith]

maybe a weak spring on a brush or brush hanging up. I have one also and haven't used it for many years, I better see how mine runs now.
Dave

 

[Chips O'Toole]

Thanks for the suggestions. I cleaned the commutator with De-Ox-Id and Scotchbrite. An eraser didn't have any effect on the dark areas. I also scraped the brushes a little with a file. Now the grinder does nothing at all. I tested the switch, and it's fine.

 

[Dave Smith]

test your wires and connections from the switch to the brushes.
Dave

 

[jbobb1]

I agree with Dave Smith. It sounds like the brushes could be hanging up in the brush holder. If you, have it apart, make sure the bushes are moving freely in their holder all the way. Sometimes the end of the bush holder (near the commutator) can prevent the brushes from making proper contact with the comm, if some arcing had been going on.

 

[Dave Smith]

I just went down to my lower shop and brought my hand dumore grinder up. it runs very good up to 22,000 rpm. mine must be an older model. cat. #10 121 ser. #8176 3084 no load rpm 22,000. 115 v 1.4amp AC-DC. I noticed that the cord rubber is cracking. just have to remove the two screws on the product tag to get to the switch and wires--very simple except that the wires are crammed in a small area. edit-- it has the very small nice Jacobs NO. 0 5/32 cap. chuck
Dave

 

[Chips O'Toole]

The connections to the brush holders are good. The voltage is there.

It looks like one of the brushes is not very excited about exiting the brush holder all the way and making good contact. I ordered new brushes. The brushes say "660" on them. I am wondering if there are standard brushes that fit all sorts of things, and 660 is a designation.

I am not sure filing the brushes was a good idea.

 

[woodchucker]

The connections to the brush holders are good. The voltage is there.

It looks like one of the brushes is not very excited about exiting the brush holder all the way and making good contact. I ordered new brushes. The brushes say "660" on them. I am wondering if there are standard brushes that fit all sorts of things, and 660 is a designation.

I am not sure filing the brushes was a good idea.

I have filed mine. Sometimes they are not making contact all across, it leads to arcing and heat, so I file them flat across and let them reseat and break in again. It will never destroy them. I have a maintenance box of assorted brushes. they are all flat. I recently had to replace the brushes in my dremel, and had to cut and file a TOO LONG brush... no issues, just took some running to break them in.

BTW years ago before brushless motors, the guys that raced them in cars (brushed) and in planes used to break their motors in , in the water. They said it was easier on the motor.. I don't know about it, seems hard on the metal and oxidation.. but what do I know.