Armature commutator segments

[Bsmith]

Bought a second hand 5" angle grinder from an auction for £2, label on it saying that it had failed the test and do not use. I reconned I had done ok because all I wanted off it was the nut that holds the disk on, (one of them once cost me £5 from a supplier).
Just for fun though and curiosity I took the grinder apart. Found the brushes were completely worn down and the commutator blackened and slightly grooved. Took the armature out and put it on the lathe, skimmed commutator with parting tool and finished with wet and dry 300 grit.
Now, I have like copper burrs between the segments of the commutator. Do I need to scrape these out or will it be ok to try with new brushes as it is?

 

[the snooper]

Just scrape them out with something you don't want them shorting, it won't end well

 

[Bsmith]

Yes that is what I thought Paul. I made a hacksaw blade hook kinda thing but the swarf or what ever is well stuck between, needs a good pull to free it. When I'm finished can I check they are not shorting with a test meter?

 

[pedrobedro]

Bought a second hand 5" angle grinder from an auction for £2, label on it saying that it had failed the test and do not use. I reconned I had done ok because all I wanted off it was the nut that holds the disk on, (one of them once cost me £5 from a supplier).
Just for fun though and curiosity I took the grinder apart. Found the brushes were completely worn down and the commutator blackened and slightly grooved. Took the armature out and put it on the lathe, skimmed commutator with parting tool and finished with wet and dry 300 grit.
Now, I have like copper burrs between the segments of the commutator. Do I need to scrape these out or will it be ok to try with new brushes as it is?

I had one that burned the brushes and I just ran the comm in a drill chuck with some 600 grit then cleaned the slots with a broken hacksaw blade and its been running for years now.

 

[the snooper]

You can get a type of grinding stone for sorting them out, I took a motor in and the guy connected it up snapped a bit of the grill out and stuck a com stick in and it sorted it out, it worked perfect, not sure if com stick is a trade name for it or what but the exist

 

[the snooper]

Bought a second hand 5" angle grinder from an auction for £2, label on it saying that it had failed the test and do not use. I reconned I had done ok because all I wanted off it was the nut that holds the disk on, (one of them once cost me £5 from a supplier).
Just for fun though and curiosity I took the grinder apart. Found the brushes were completely worn down and the commutator blackened and slightly grooved. Took the armature out and put it on the lathe, skimmed commutator with parting tool and finished with wet and dry 300 grit.
Now, I have like copper burrs between the segments of the commutator. Do I need to scrape these out or will it be ok to try with new brushes as it is?

Maybe a fine junior hacksaw blade would clean them up

 

[Bsmith]

Would be great with junior hacksaw if I could get a straight go at it, but it steps up where the wires leave the segments and go into the armature, this is the corner where I'm having difficulty getting the bits out.

 

[Bsmith]

Been thinking of making something to go in the dremmel to try.

 

[the snooper]

How about a stanley blade, just slice it off

 

[Seadog]

Wet and dry is not a good way to clean the commutator. The abrasive embeds itself in the copper. Glass paper (sand paper) is what you should use.

 

[Seadog]

I don't think the shedding is the problem. It's just that emery embeds itself into the copper and and is also conductive.

 

[dobbslc]

Com stick! We used them for cleaning the comms on RC car motors years ago.
It's just a bunch of GRP fibres in a plastic tube.

 

[the snooper]

I don't think the shedding is the problem. It's just that emery embeds itself into the copper and and is also conductive.

Are we talking emery or wet n dry both are different

 

[the snooper]

Com stick! We used them for cleaning the comms on RC car motors years ago.
It's just a bunch of GRP fibres in a plastic tube.

These are stones, see here http://www.martindaleco.com/abrasives.htm

 

[Bsmith]

I'll get there somehow, any way I can test that the segments are not shorting together when I'm finished? The spaces/ insulators between are very narrow.

 

[the snooper]

I'll get there somehow, any way I can test that the segments are not shorting together when I'm finished? The spaces/ insulators between are very narrow.

Just scrape between them, a good magnifying glass will let you see and copper touching

 

[Seadog]

OK Snooper, emery is the one to steer clear of. I thought they were one and the same, but clearly not (aluminium oxide as against silicon carbide).

any way I can test that the segments are not shorting together when I'm finished

The resistance typically is very low, so, without a meter that has a low resistance range, we're talking 0.5 to maybe 3 Ohms, you'll have a difficult time measuring between segments. There used to be a piece of equipment called a growler that was commonly found in rewind shops that could detect shorted segments.

 

[Robotstar5]

One of the jobs I hated as an apprentice was undercutting the comm on a motor using a broken hacksaw blade with tape wrapped round it as a handle

 

[rtbcomp]

From memory you undercut motor commutators slightly (ie cut the insulation so it sits slightly below the copper) but don't undercut dynamos.

EDIT Looks like my memory fails me, see post. #24

 

[lotus 30]

i bought 3 chemo angle grinders from aldi or somewhere well my wife did she rang me from a ship and said they have angle grinders in store at £9.99 each do you want me to get one no get three. they lasted about 10 hours each and burnt the brushes out they came with spare brushes so fitted them all three burnt out completely in no time. Bought a makita for £40 to replace them had it for six years just grease to keep that running.
I have had a smaller hitatchi for prob 30 years one bearing and just fitted (well made one fit) brushes THEY JUST DONT MAKE EM LIKE THEY USED TO
rant over