Armature commutator segments

[500e]

Remember that well Robotstar an old 5 Hp motor or larger finger all cramped up nicks where the you had not noticed you were griping the blade not the handle, then polish with the fiber glass stick.
If people use hacksaw blade remember to grind the set off the blade you only want to cut the insulation not the copper.
You need to get the cut so it cleans the gap leaving no remnants of the insulation on the sides of the cut, if left as wear takes place it breaks off damages brushes & increases wear a vicious circle.
CPC sell fiber glass pens for around 90p will do for light work not a quality item.
It is starters you don't undercut.

 

[Bsmith]

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

Yes lotus 30, I've had a 9" Hitachi for around 30 years, gone through 2 sets of brushes but still going good.

 

[rtbcomp]

This recommends undercutting both starters & dynamos, my Riley workshop manual says one or the other, but it's packed away at the moment.

 

[arther dailey]

the rule is cut to the same depth as the insulation is wide, again as an apprentice sitting on a tail stock of a lathe as it was safer than the tall axle stands,took hours .......

 

[rtbcomp]

...my Riley workshop manual says one or the other, but it's packed away at the moment.

Found it, undercut dynamo, don't undercut starter, Lucas M418G, M45G.



Of course it could depend on make/year/model so if in doubt contact the manufacturer.

 

[arther dailey]

on a starter it is because the amperage drawn , this causes next sgment coming around to arc accross the gap ,eroding both segments and blowing brushes.

 

[500e]

A rule of thumb is carbon brush undercut a copper brush don't, I think the other reason would be that copper dust (wear) would build up in the undercut & short segments

 

[Anguz]

commutator stone is what you need

 

[Farside]

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?

You're lucky there's any reusable thickness to the segments at all. Cheapy universal motors are made down to a price, as you would expect, and thin commutators are one way to shave costs. If it's a decent make, it's not so much of a problem.

 

[Bsmith]

You're lucky there's any reusable thickness to the segments at all. Cheapy universal motors are made down to a price, as you would expect, and thin commutators are one way to shave costs. If it's a decent make, it's not so much of a problem.

I would say it's a cheap CE 5" angle grinder, came with 9" disk attached and no guard. I only took enough off the comm segments to clean them up and remove slight grooves (prob a 2 - 5 thou) but I think the segments are thick enough. 5 sets of brushes ordered from China via eBay for £1.14p inc post, have to wait a few weeks till they arrive. Will upload photo of armature soon.

 

[Exuptoy]

Cheap grinders aren't worth a ****. I bought one form MM, it was the Practical Classics recommended one when I started restoring my VW Bay ended up taking it back then the second one was replaced and the guy said don't bother mate, pay an extra £20 odds and have the Makita. I'm still using it now 5 years later.

 

[zeppelin builder]

glass paper is correct

emery embeds in soft metals. thats an old gunsmith method a lead or hard wood slug treated with emery powder is inserted down the bore and stroked as its rotated ,honing a miniscule amount of metal off

 

[Bsmith]

You're lucky there's any reusable thickness to the segments at all. Cheapy universal motors are made down to a price, as you would expect, and thin commutators are one way to shave costs. If it's a decent make, it's not so much of a problem.

Checked today, the comm segments are prob around 4mm thick, now my bl00die camera isn't working well for close ups......