07-06-2020, 09:58 AM
Ivor,
Not sure if you've already done this bit I was amazed how poorly the new brushes I fitted matched the curvature of the commutator.
I hadn't noticed this until I completely removed the armature from the motor body and then fitted just the brush end plate onto the armature spindle and had a look.
Although the radius on the brushes was probably correct, because the brush holder swings in an arc the commutator was actually only bearing on a very narrow land across the width of the brush. Using a strip of abrasive paper curved around the commutator and pulling it back and forth under the pressure of the brush I effectively re-formed the curve until it mated much better.
When I powered the re-assembled motor with jump leads the spark as I made contact was much more pronounced than previously, presumably because the motor was now drawing more current.
Anyway, it was after this that it seemed to work OK so if you've not done so it may be worth a try.
Incidentally, many years ago when I was an apprentice I was told it was best to use sand paper rather than emery on brass or bronze bearing surfaces as otherwise the abrasive can become embedded in the surface. Not sure how true this is but the old fitter who passed it on was very experienced.
John.
Not sure if you've already done this bit I was amazed how poorly the new brushes I fitted matched the curvature of the commutator.
I hadn't noticed this until I completely removed the armature from the motor body and then fitted just the brush end plate onto the armature spindle and had a look.
Although the radius on the brushes was probably correct, because the brush holder swings in an arc the commutator was actually only bearing on a very narrow land across the width of the brush. Using a strip of abrasive paper curved around the commutator and pulling it back and forth under the pressure of the brush I effectively re-formed the curve until it mated much better.
When I powered the re-assembled motor with jump leads the spark as I made contact was much more pronounced than previously, presumably because the motor was now drawing more current.
Anyway, it was after this that it seemed to work OK so if you've not done so it may be worth a try.
Incidentally, many years ago when I was an apprentice I was told it was best to use sand paper rather than emery on brass or bronze bearing surfaces as otherwise the abrasive can become embedded in the surface. Not sure how true this is but the old fitter who passed it on was very experienced.
John.
