Problem with my circular saw

Stan in Oly, WA · Feb 23, 2015

I was using my Skil 77 worm drive saw pretty hard this afternoon and it started acting like there was a problem. I could hear the sound of the brushes arcing on the armature---that sound like a welding arc makes. Looking in the back end of the saw I could see arcs from the brushes running a third of the way around the circumference of the armature. I let the saw cool down, then took out the brushes and inspected them. They appeared normal. I blew out the saw and put the brushes back in, but it didn't change the situation. What's happening, and what can I do about it?

Thanks,

Stan

Lou from Wi. · Feb 23, 2015

take the brushes out then take a continuity meter and check the armature. It shouldn't show continuity while you spin the armature by hand using the blade as a turning device for the armature.DO NOT FORGET TO UNPLUG THE SAW WHEN TESTING.lol.Sounds to me like you have a serration gone bad in the armature and is grounding out.By continuing running it you'll lose it all, you'll smell it being burnt.
LOU

Lou from Wi. · Feb 23, 2015

my mistake I should have said commutater instead of armature.link below for a better explaination. We check from the commutator to the armature shaft for resistance,which there should be none. Hope this helps.
LOU
poke here for testing armature

Fatamus · Feb 23, 2015

(quoted from post at 20:02:55 02/23/15) I was using my Skil 77 worm drive saw pretty hard this afternoon and it started acting like there was a problem. I could hear the sound of the brushes arcing on the armature---that sound like a welding arc makes. Looking in the back end of the saw I could see arcs from the brushes running a third of the way around the circumference of the armature. I let the saw cool down, then took out the brushes and inspected them. They appeared normal. I blew out the saw and put the brushes back in, but it didn't change the situation. What's happening, and what can I do about it?

Thanks,

Stan

It sounds like your bushings are bad allowing the armature to come into contact with the exciting coils. Also you might look at the armature and the exciting coils for starches where they would be rubbing each other..
ALSO..
The commutator, the copper looking thing on the end where the brushes come into contact, copper leads cannot touch each other.
and check the leads going to the brushes, they may be grounding out ageist the housing.

Bob · Feb 23, 2015

"We check from the commutator to the armature shaft for resistance,which there should be none."

Sounds like you like SHORTS!

INFINITE resistance is the term you are looking for, 'ol Louie!

Bob · Feb 23, 2015

Likely, you have an internal short(s) in the armature windings.

Lou from Wi. · Feb 23, 2015

nice to be corrected by world renowned professor of what,young bub.lol.
LOU

Geo-TH,In · Feb 24, 2015

I always polish the commutator with 3-400 wet/dry sand paper. Clean out the segments. Sometimes a tooth pick will work, sometimes a razor blade to get between segments. If brushes are long, you commutator doesn't have a deep grove in it from the brushes, you have a lot of flash over, you most likely will need a new armature. In many cases, time for a new saw.

I know worm drives are thought of as a commercial saw. 25 years ago I purchased a dewalt saw, not a worm drive. I'm right handed and the worm drive saws seem to put sawdust in my face/eyes. The conventional dewalt saw doesn't.

My dewalt saw is bad about cutting the cord, so you may want to find a different saw.

Butch(OH) · Feb 24, 2015

My old Skill 6 1/2" saw did the same thing last fall. Brushes looked like lots of life left in them but there is a cable inside of the spring that limits brush travel so they can not wear all the way down and get gobbled up by the armature. To test to see if that is the problem you can nip the cable and reinstall them. If it works be sure to find some new brushes pronto.

Stephen Newell · Feb 25, 2015

Yea the brushes are toast. It's not too difficult to change the brushes however it would probably work better if you would dismantle the saw and clean the commutator as well. Usually when the brushes start arcing it leaves deposits on the commutator. If removed from the saw I normally use 0000 steel wool and then blow it off with compressed air.

Problem with my circular saw

Stan in Oly, WA

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Lou from Wi.

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Lou from Wi.

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Fatamus

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Bob

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Bob

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Lou from Wi.

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Geo-TH,In

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Butch(OH)

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Stephen Newell

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