|COMMUTATOR BRUSH REPAIR |
|PART NO SP-088-0504|
I tend to do lots of small repair jobs. Here is a brush repair job on a shower pump motor.
My mate's shower pump stopped working. If he hit it, it would start up briefly. Eventually it stopped altogether.
I started at the plug and steadily worked my way through the system, testing each part of the pump assembly, and ended up stripping it completely. Long story short, the brushes had totally worn.
New brushes were 28 GB Pounds a pair ... crikey. It did not seem worthwhile throwing 28 pounds at a 10 year old shower pump.
I had an assortment of used brushes from some old washing machine motors, so decided to try those. Trouble was, they were not the correct size.
I decided to grind them to size on the lathe. I had to be accurate first time on this job, as I only had two pairs of replacement brushes to play with.
↓ The old brushes are on the left. The replacement brushes are on the right. Luckily, the replacement brushes are the same thickness, but are far too wide.
The brushes need to be 4.8mm thick and 7.8mm wide.
↓ The old brushes had worn down completely and the braided wire was rubbing on the commutator.
You can see the braid showing through the curved part of the brush that rides on the commutator.
↓ I found a scrap piece of aluminium and proceeded to make a holder, to accurately hold the brushes during grinding.
I mounted the milling cutter in the lathe chuck and milled a 5mm wide slot in the edge of the piece.
↓ I faced the edge, so the slot ended up at 8mm deep.
↓ I drilled two 2mm holes.
↓ I tapped the holes M2.5, and inserted two screws.
↓ The screws secure the brushes in the holder during machining.
↓ I mounted a fine cup grinding wheel in an arbor in the lathe chuck.
↓ I slowly reduced the two edges of the brush, making sure the braid was on center.
↓ Eventually the brush was ground flush with the side of the holder, and was 8mm wide.
↓ The brushes were now close to 4.8mm x 7.8mm and seemed a good fit in the holder on the motor.
I know there is much technical stuff concerning motor brushes, but I've no time to get into that now. Wing and a prayer on this one.
↓ The ends of the brushes needed forming, to match the curve of the commutator.
I measured the commutator at roughly 25mm diameter.
I mounted an el cheapo 'hobby' type grinding wheel in the lathe chuck and used a diamond dresser and trimmed the wheel to 25mm diameter.
I reused the scrap holder to hold the brushes for this operation.
↓ I could not alter the height of the scrap holder that was mounted in the lathe tool holder.
After a bit of thought I realised I could pack up the top-slide assembly, to bring the brush to center height. That's a first for me!
↓ I slowly ground each brush to the correct length, and formed the correct curvature to match the commutator.
↓ Here is the formed curve.
↓ Finally got it reassembled.
I always try and keep things repaired and running.
(Never, ever, pull the plug on my life support machine).