Orbital sander not working - brushes?

[Charlie George]

You can buy a replacement on Ebay top bid at moment is £4.99.
https://www.ebay.co.uk/itm/Black-De...080643?hash=item4db3074803:g:qUgAAOSwZXRfWINH

 

[Burnerman]

I think the brushes are fine.....so long as you can pull them back against their spring and they move, alls well enough!
Is there any excess sparking taking place?
John

 

[phatboy]

I think the brushes are fine.....so long as you can pull them back against their spring and they move, alls well enough!
Is there any excess sparking taking place?
John

Thanks, there is a bit of sparking, doesn't look too serious though. The brushes can be pushed back onto the springs and when released seem to connect to the comm.

Tim

 

[Burnerman]

A bit difficult to explain Tim but on occasion I've found when power tool motors are about to go AWOL they tend to admit more of a growl than a typical motor whine.
If it's going slow maybe it's the shuffle plate gears needing lube but I don't think things look too good!
Valuable experience though.
John

 

[conny]

Arrrrgh! Carborundum paper NO!!!! It does contain metallic bits and these will settle between the comm segments and be part of the cause of sparks. I can't believe the shops you went to have never heard of glass paper. Most people know it as sand paper but sand paper doesn't actually exist as such. Glass paper/sand paper is what you buy from places like B&Q, Homebase etc to 'sand' down your paintwork before painting. Don't use water to clean anything electrical. You will introduce damp into the mica insulation between the comm segments and it will cause low resistance between the bars. Dry air is the best for cleaning armatures and comms unless you have a workshop that contains the correct equipment. As stated above, if you can push the brushes back into the box and they spring back into position 'with a nice slapping sound' then they are probably ok. They certainly look ok in the picture with no signs of burning on the ends. Now for a difficult bit. It would help if you could clean out the grooves between the comm segments with a small hacksaw blade. It's much easier if the armature is out of the machine but can be done in situ. Using a small broken piece of hacksaw you need to 'GENTLY' scrape along each groove till you can see the lighter mica underneath but don't dig it in, just gently scrape away between every bar and then brush and vacuum the dust away. Do not use any liquids unless it is a specifically designed electrical cleaner that quickly evaporates.

 

[phatboy]

Thanks guys, lots of good info here!

I bid and won the same model as posted by @Charlie George - £9 can't go far wrong!

However, I will persist with fixing this one, for no other reasons than I don't like being defeated, and it's valuable learning! I better get some contact cleaner though....

Tim

 

[big-all]

my thruppence worth
if its been stored in a cold damp shed over winter
the brushes can glaze over
so you clean the brushes with a needle file or fine emery then fully clean
you polish the commutator with brasso or metal polish " NOTHING MORE ABRASIVE"

to release the brushes you may need to remove the motor and circuit board as one from the case its all by trial and error but not force and once cleaned you will have to tape or whatever to hold the brushes back until the circuit board it over the comutator then work the tape out

 

[conny]

Don't use brasso or metal polish! You do not want to get any liquids or solvents near the commutator unless they are electrical cleaning solvents which evaporate. To clean the comm you can thread a length of fine sand/glass paper under the brushes, (grit side to the comm), and gently rotate the armature by hand as I described above.
The brushes can be bedded in, (shaped to the exact curve of the comm), by again sliding a strip of fine sand/glass paper around the comm under the brushes but this time have the grit side face up so the brushes are rubbing against the grit side. Again, rotate the armature by hand but this time it will only take a few turns to shape the ends of the brushes to the correct curve. Vacuum all dust away and look at both sides of the brush to see they are sharp edged and touching the commutator evenly. These steps will help to reduce, and hopefully eliminate, most if not all sparking at the comm though you will still probably get a few when under load.
Good to see that now you have a replacement you can use this one to learn on.