Miter saw acting slightly weird

[dwasifar]

I have a Delta 12" "sliding" miter saw. (It doesn't actually slide, it has hinged arms instead, but that sort of device.) It's new Delta, not the old school brand.

Recently I had a project requiring about 60 short repetitive cuts, and by the time I got toward the end of them, I noticed the saw was kind of stuttering and hesitating for about a second each time I started it. It would then come up to speed normally.

After I finished all the cuts, I pulled the brushes thinking perhaps they needed to be replaced. There was plenty of material left on them, but I did see a little bit of what looked like oxidization on one edge of each brush. I rotated the brushes 180 degrees and reinstalled them. The saw behaved normally after that, but I'm not sure if it was because of what I did, or just because it had a chance to cool.

Opinions?

 

[The Cobbler]

I would check the power lead for breaks,especially where it bends /moves . the switch for good continuity,all connections are snug/tight... and the armature /brushes for a lot of sparking. look at the commutator on the armature for any different looking commutator bars .
any one of them could be first on the list as far as I'm concerned
if the armature is bad it often shows heavy marks burn/erosion on the brushes and blacked bars near where the windings connect, also comm bars usually heat up & raise off the commutator

 

[dwasifar]

I would check the power lead for breaks,especially where it bends /moves . the switch for good continuity,all connections are snug/tight... and the armature /brushes for a lot of sparking. look at the commutator on the armature for any different looking commutator bars .
any one of them could be first on the list as far as I'm concerned
if the armature is bad it often shows heavy marks burn/erosion on the brushes and blacked bars near where the windings connect, also comm bars usually heat up & raise off the commutator

Thanks, this fits with what I saw on the brushes. Will check it out.

 

[dwasifar]

Actually it turned out to be a mechanical problem, not electrical at all.

I'm using one of those add-on lasers that replaces the outer cup washer and shines a beam down the face of the blade. The problem with these they are not cupped. They have a very slight recess on the back:



When I first started using it, I had to go shopping for a thinner arbor adapter washer, because the stock one was thicker than the saw blade. So when I cranked down the bolt using the laser in place of the cup washer, it contacted the arbor adapter before it touched the blade, leaving the blade loose. I wound up stacking two thin washers to replace the arbor adapter.

That's worked for years. But gradually the contact area between the blade face and the back of the laser has apparently started to slip. Over time it ground away just a little surface area, which was enough to cause the too-thick arbor adapter problem to recur. What I was experiencing as hesitation and stutter was the blade not coming up to speed in sync with the motor. The handle was actually jumping around in my hand. When it started making more obvious (and ominous) mechanical noises, I went poking around and figured it out.

I smoothed out the damaged contact surfaces of the blade and the laser, and removed one of the two stacked washers from the arbor. That seems to have fixed it, but I'll be keeping an eye on it.

I like the laser, but they all seem to have this same design flaw.

 

[The Cobbler]

That's better than a burned armature!

 

[dnschmidt]

Another example of why a shadow line is superior to a laser. Sometimes low tech beats high tech.