What do the blue sparks mean

[pierhogunn]

What does it mean when there is a slight scraping noise, blue sparks, a burning electrical smell, and the blade now runs down slowly when the power is cut to the saw?

I was ripping a 1X6 last night, and got the neatest light show out of the butt end of the motor on my beloved ( and quite necessary to my current project) bt3100?

any help, or procedures to fix this are greatly appreciated

[Stytooner]

Sounds like motor bearing failure. Probably time to select the head stone style and epithet.

[msorelle]

Sounds like you let the magic smoke out of the motor

I'm with Lee, probably time to stick a fork in it, I suspect it's done.

Mike

[RayintheUK]

About the only thing you can do is to have a look at the brushes and give the armature a clean. If the brush(es) wore out, that might account for the slight scraping noise, as the spring hit the armature. Otherwise, I suspect it's a main bearing and perhaps some other collateral damage - beyond economic repair, but there are occasionally a motor or two kicking about on the forum. Good luck!

Ray.

[eezlock]

what do the blue sparks mean?

Hello Dan, I see that you don't live too far from me....I'm in Charlotte, so I would recommend that you call Dixie Electric Motor Service on Freedom Dr.
They may be able to repair the motor for you...and maybe cheaper than buying a new one. I did check on e-bay, a couple of sellers parting out their saws...but, you might want to think about buying a used motor sight un-seen and un-tested, a pig in a poke situation as they used to say.
Hope this helps...eezlock

[mpc]

With the saw unplugged, open the side panel and the dust cover on the blade housing. Remove the blade. Turn the arbor by hand and see how tight it feels. If it turns easily then it's not the bearings inside the motor. If it feels hard to turn, and especially if it is harder in spots than others (or feels gritty), then one or both bearings on the main motor shaft are damaged.

They are generic sealed bearings; I just replaced the one on the brush end of my saw this weekend... the bearing itself cost under two bucks from Fastenal down the street. They had the right size sealed bearings on the shelf. (the front and rear bearing on the motor are different sizes by the way; the sizes are stamped into the bearings) It takes a while - you have to disassemble darn near the whole saw. Getting the old bearing off the motor shaft isn't easy without the right tools; I do a lot of car stuff so I have a bearing press and puller tools. You'll need two somethings that are flat with half-circle holes cut into them (or take a 1/8" to 1/4" thick flat chunk of metal, drill a hole in it a little bigger than the motor's shaft, and then cut the metal in half) to fit around the motor shaft underneath the bad bearing. Then you push the shaft out of the bearing, letting the tool hold onto the bearing. Typical 2 or 3 jaw bearing pullers might be an option if you have/find a smaller model; the normal sized one I had was too fat to fit between the bearing and the rest of the motor armature.

Here's a pic of the type of tool I tried to describe:
http://www.harborfreight.com/cpi/cta...emnumber=30305
Look at the big thing in the center of the pic; you can see how it fits around the motor shaft and underneath the bearing. Ignore the other stuff in the pic - only the center item matters.

With the motor apart, you'll be able to eyeball it for obvious burned/charred/melted wiring though a motor repair shop will be able to do a far better inspection.

mpc

[big tim]

Sounds like brushes to me!

Tim

[pierhogunn]

okay, MPC you have given me a ray of hope, this project ate my dewalt jig saw, and I thought that it had KO'ded my saw.

I rotated the blade by hand, and it doesn't move with any more resistance than it did before, nice and smooth with no tight feeling sections,

I did however count 7 clickity-click sounds as I turned the blade through 1 full rotation ( counted them by marking and numbering on the blade where I heard each one)

Now, with my extremly limited knowledge of electrical motors, I would hazard a guess that the clickity click sound is the sound of one or more worn brushes, or the springs that push the brushes against the armiture clicking as the different sections of the armiture slips past it...

so next question, which is jumping ahead of taking my saw apart, where do I get replacement brushes?

[crokett]

Here is a link to electric motor repair search for Charlotte:

http://www.google.com/search?sourcei...r+charlotte+nc

[Alex Franke]

Don't know if this will help you, but mine was sparking when I first got it actually -- probably 5 or so years ago. Having no easy way return the saw, I took the motor apart and discovered a loose wire. I don't remember much more than that -- other than it being very difficult to reach and refasten. It's worked fine ever since.

Good luck though.

[mpc]

I don't know the gearing ratio of the belts... but the saw motor turns several turns for each turn of the blade. Just from memory of the belt sprocket sizes, I'd guess around 3 or 4 to 1?

So 7 clicks probably means ONE bad spot "clicking" past the two brushes.

To see if it really is the brushes, or something in that area, pop the other side panel off the saw - the one with the electrical outlet. Look at the back of the motor, you'll see part of it is just a cover plate held on by two phillips screws... unless the later motors are totally different than my early 13-amp job. With that cover off, you'll see the rear bearing (and probably a load of sawdust) and the two gold colored carriers for the brushes. Shine a flashlight on them while you turn the blade again, see if you can spot either brush moving during the clicks, or if one of the commutator (turning part of the motor) contacts has "lifted" from it's glue-bond.

On my saw, there is a small phillips screw holding a brown fiberboard plate on each brush carrier, remove those and the gold box with the brush lifts out. See if the business end of the brush looks burned/pitted; I ran mine over a gently curved piece of 220 sandpaper and got rid of that junk - the motor is definately more powerful now.

mpc

[pierhogunn]

I know what I am doing as soon as I get my kids in the bed, anyone know where I can get a set of brushes for this motor, in Charlotte, PDQ?

[unknown poster]

Check Sears Parts for brushes for a 315.21829000. Their website seems to be broken right now, but if you search for that model number you should be able to see if they sell just the brushes. If sears parts department has it, there's a store in Pineville that might have it PDQ.

[pierhogunn]

awesome, thanks Unknown, say you would happen to know Unknown Henson would you?

heard he was named after his father...

[Jack Vines]

mine was a short in the armature -toast

Hope you have better luck, but I disassembled it cleaned the area on which the brushes ride, but it there is a leak in the commutator which is which is letting the smoke out of the armature :>)

thnx, jack vines