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#1 Robert BG

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Posted 25 June 2016 - 09:40 AM

I just noticed what looks like solder on a new arm that was freshly cut. It's so light it looks more like a stain but after break in the grooves are full. I'm about to tear it down and I'm sure it will have to be recut but I was wondering if anyone has come across anything similar.

 

Also what does everyone use to clean com grooves. I always just ran a sharp needle or pin through them.


Robert Fothergill




#2 Bill from NH

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Posted 25 June 2016 - 10:02 AM

I cut a bevel on the ends of round toothpicks for cleaning out comm slots. If I slip, the wood won't scratch the comm like X-Acto blades and other metal items. Scratches may be overated, I once read that some will steel-wool their freshly-cut comms before loading an  arm.


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#3 Robert BG

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Posted 25 June 2016 - 10:26 AM

I'm nervous with the X-Acto method myself.

 

As for scratches I used to use 1500 grit wet dry before on all my comms before putting a set-up together but someone advised against it and I stopped. Although I'm not sure why I took their advice to heart like I did because they were slower LOL. But I was young at the time so who knows.

 

I might give it a shot again. All I did was wet the paper and twist the comm through it once or twice to smooth everything out and it seemed to work. There were times I didnt have the time or money to send off arms and also used it as a ghetto type rebuild and while I don't recommend it, it did help times over not doing it on a old arm and I squeezed another race or two between rebuilds.


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#4 havlicek

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Posted 25 June 2016 - 11:47 AM

I've never found anything that works better than dragging (not pushing) the back of a #11 X-Acto blade down the comm slot from the bottom towards the top. It's easy and the blade seems to be about the perfect width for most comm slots.

 

I use superfine synthetic steel wool (Scotch-brite) for cleaning comms, but not after they've been cut.

 

-john


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#5 MSwiss

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Posted 25 June 2016 - 11:53 AM

Also what does everyone use to clean com grooves.I always just ran a sharp needle or pin through them.

You really don't want to use anything that's tapered or comes to a point.

 

You won't be able to clean out the bottom corners , or it will take more effort.

 

If you're dealing with a slot that might have a bit of epoxy in there, an X-Acto #11, Dremeled to the profile of a slot, works well.

 

If you raise a burr, so what, it will quickly arc away in break-in.

 

On my own arms, that had been run a few times, I would use a pc. of .010" Lexan®, and also, if ambitious, also do the cleaning  under a microscope.

 

All a bit of overkill, as if there was a pc. of copper still in the slot, you will know it as the arm won't spin freely when assembling the motor, before installing the brushes and springs.


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Mike Swiss
 
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#6 Ramcatlarry

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Posted 26 June 2016 - 09:42 AM

Cutting all commutators also leaves a very sharp edge at the slot, which CAN give both very good timing and help wear your brushes quicker - since it is a chisel edge.  A great use for an old ball point pen is to use it to BURNISH (roll down) that edge so that it is more of a very small ramp instead of a knife.  Used this technique cutting comms on generators and starter armatures as well as slot cars.


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#7 Robert BG

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Posted 27 June 2016 - 07:18 PM

 

All a bit of overkill, as if there was a pc. of copper still in the slot, you will know it as the arm won't spin freely when assembling the motor, before installing the brushes and springs.

What do you mean by this?

Will it actually cause funky things in the magnetic field even with no brushes installed?

If so that would explain a motor I recently attempted to assemble.It wasnt constantly but every couple of turns it would seem like something was hanging up mechanically.

I kept checking for a mechanical hangup but there wasnt anything.But I tore it down and started again anyways.

I've built a few motors but never saw anything like it.I knew something was wrong but wasnt sure what at the time.


Robert Fothergill

#8 MSwiss

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Posted 27 June 2016 - 08:58 PM

Yes, if there is anything conductive in the slot, bridging from one segment to another, the arm won't spin freely.

 

It's shorting the 2 segments.

 

You'll feel side play, good bearing alignment, and when you spin it, before installing the brushes and springs, it will rotate, but not like it should.

 

And junk, in more than one segment,  the lousier it will spin.

 

An arm, before cleaning, with chips in all 3 slots, will barely rotate.


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Mike Swiss
 
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Two-time G7 World Champion (1988, 1990)
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#9 Robert BG

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Posted 27 June 2016 - 09:21 PM

This one was intermittent but that explains it.

I've never put one together with crap in there that did this,so I guess I was lucky.

Not that I didnt believe you but I guess this proves that I shouldnt keep cleaning them the same way,I must have missed something in the end somehow and it was floating around in there.It would spin perfectly a few times and then bam it was like someone hit the brakes.


Robert Fothergill

#10 MSwiss

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Posted 27 June 2016 - 09:29 PM

The metal piece must of been small enough it didn't always touch both sides at once.

 

Pick up a microscope at a flea market.

 

It comes in handy at times, for stuff like that, and especially good for removing slivers.


Mike Swiss
 
IRRA® Components Committee Chairman
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Two-time G7 World Champion (1988, 1990)
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mikeswiss86@hotmail.com (also my PayPal address) 
Note: Send all USPS packages and mail to: 5858 Chase Ave., Downers Grove, IL 60516
Make checks out to Chicagoland Woodworking, Inc.


#11 Robert BG

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Posted 27 June 2016 - 10:05 PM

I ordered a otoscope on the suggestion of a member here already that has yet to arrive and I'll  probably dig out my old microscope and keep it near my bench for now.My eyes sure arent as good as they used to be when I was younger so they should make it easier.

I also tossed around the idea of getting a digital microscope for electronics work but I figured I'd rarely use it enough to justify getting a decent one.So I might look into that again.They can be great for doing work under on small things and I already have a monitor on my work desk.So thats another option to look into and this is probably as good of a excuse to put me over the edge and buy a decent entry level one.


Robert Fothergill





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