Author Topic: Repair a commutator?  (Read 1699 times)

Offline RussellT

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Repair a commutator?
« on: September 03, 2016, 11:08:46 AM »
I mentioned to a friend that I was thinking of buying a router and he said, "I've got one in bits you can have if you can mend it."

I've got the box of bits and attempted the jigsaw to see if it's all there.  It seems I'm missing two clamps that hold down the motor brush boxes and two screws that hold the top of the casing on.

However the original fault looks tricky to mend.  The commutator has two loose segments - pictures attached.  A replacement armature is not available.  I could get an armature and field windings for 145 but another friend offered me quite a good router for less than that..

I was wondering whether it would be possible to epoxy the loose segments in place and skim the commutator - but with the centrifugal force and possible high temperature I am a bit doubtful whether that would work.

I'd be grateful for any advice or suggestions.

Russell

Offline JHovel

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Re: Repair a commutator?
« Reply #1 on: September 03, 2016, 11:38:32 AM »
My thoughts are: the wiring looks pretty good on the armature. So it didn't overheat and cause the delamination of the armature.
So it is very likely that the original bonding or rather moulding in of the strips didn't manage to resist centrifugal forces.
Just gluing them back in - with a potentially lower strenght method than original - isn't going to do it for very long.
However the comutator strips are quite thick. The rub marks from the carbon brushes are also quite a bit narrower than the commutator. So I would glue them and then skim it GENTLY. Then cut a step or groove in the bits not touched by the brushes. In that step or the groove, I would force/press some kind of non-conductive ring. Maybe a thin plastic one and a steel hoop on top of it?
In any case, you will have to make it stronger than it was new.....
Cheers,
Joe
Cheers,
Joe

Offline Joules

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Re: Repair a commutator?
« Reply #2 on: September 03, 2016, 11:51:52 AM »
I would attempt by removing as much material between the loose strips to give enough surface to bond too but not enough to loose its position.  Do you have a large area of bonded strips still ?  Heat up the commutator to 40 ℃ and apply liberal slow set Araldite all over.  Wrap in pvc/teflon tape, add masking tape on top then use a Jubilee clip with the knuckle against a good part of the commutator to pull it all together and leave to set for a couple of days.  Skim the commutator between centres with a VERY sharp tool to take off excess epoxy and level the surface.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Online awemawson

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Re: Repair a commutator?
« Reply #3 on: September 03, 2016, 12:44:38 PM »
Many years ago (1968 I think) I was on holiday in Italy with the then girlfriend in my Frog Eyed Sprite when the dynamo packed in. No Lucas bits anywhere near so I pulled it apart to find lose commutator segments. My emergency kit included Araldite so with a hack saw blade I cleared material from between the segments, washed it clean with meths and forced Araldite in as far as I could. In the morning I carefully sanded the commutator then undercut the repaired bit with the hacksaw blade. Worked a treat and was still working when I sold the cqr several years later  :ddb:

Ironically we were travelling in convoy with the girlfriends parents and a few days later his starter motor packed in - this time worn down brushes. None available locally but a local garage had some that were somewhat larger. Bought a file, filed them to size and off he went.

Hardest part of both these incidents was cleaning myself up on a camp site - messy stuff graphite :bang:
Andrew Mawson
East Sussex

Offline mcostello

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Re: Repair a commutator?
« Reply #4 on: September 03, 2016, 02:13:40 PM »
Bravo, well played! :beer:
High Speed steel in a Carbide world.

Offline RussellT

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Re: Repair a commutator?
« Reply #5 on: September 03, 2016, 02:37:07 PM »
Thanks Joe, Joules, Andrew

You've all confirmed my view that it's worth having a go.

Joe - yes I've been wondering about making it stronger than the original.  I don't fancy pressing rings in place - making sure they stay in place seems tricky.  I was wondering about cutting a groove in the unbrushed end of the commutator and winding some epoxy soaked fibre glass thread into it.  I don't know how much I could get in there as it's not a lot of space but it might help.  At the windings end there's a fair bit of space so I could do the same there without cutting a groove.

Joules - I assume you're thinking of reducing the viscosity of the Araldite by warming it up to try and get it under the commutator segments.

Andrew - Thanks for the encouragement - like you I can't buy a replacement so there's nothing to lose by trying.

Russell