The electric motor in my circular saw has started to arc round the brushes - lighting up the underneath of the saw table. I took out the brushes but couldn't see anything wrong. There was about
10mm of carbon and when reinserted the spring was compressed so the brush was pressing against the commutator. Is there anything else that could be wrong and is straightforward to check out and deal with?The saw is a Bosch GKS 85S
Normally a symptom of one or more armature windings being open circuit, so there is no back emf as the brushes pass from one pair of commutator segments to the next.
Test (with power off) by using a multimeter between each opposite pair of segments. The resistance should be sensibly constant.
If a winding is open circuit, it's normally time for a new armature, but it's just possible that one end of the winding has become detached from the commutator, in chich case re-soldering might be possible.
10 mm sounds a little short to me, although I don't know this saw. Check for spares on the web, you will sometimes find a photo
or a diagram like this
A Bosch may well be worth a rewind. But I'm not fully convinced by this diagnosis.
NT
=A3100 + VAT - which is a lot for a handheld circular saw.
That's a great site. The exploded view of my machine could be very helpful. I tried measuring armature winding resistance via the brushes. Nothing seemed suspicious - the readings were all about 1.5ohm. WikiDiy almost as helpful as his group and encourages me to expose the commutator for visual inspection and possibly cleaning up.
Thanks everybody.
Yup. My table saw has gone exactly the same way (Performance Power Pro). Spares apparently not available ... until I spotted that Axminster used to sell the identical machine (except for colour and badging). £110 for a new one - I didn't even ask whether that was plus or inc. VAT :(
SteveW
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