What do the Blue Sparks Mean, Part II

[pierhogunn]

I took the brushes out yesterday and both are still about 3/4" long

so that's not the problem,

what is the problem is that the part of the motor shaft where the brushes touch those little copper strips.

One of the strips is raised a little, about 1/64th of an inch

so I used the saw one last time last night with no ill effects, and I was able to rip 8 3" X 32" pieces of synergite with only a strong electrical smell.

I will be taking this motor to a local eltro-mechanical shop ASAP to get this back in working order

any thoughts as to what I may have done to screw up my beloved saw?

[rjwaldren]

Maybe a foriegn object made it's way through the motor casing, there's no real path for that though. I'd expect it was just weakly held at manufacture, rare but it happens. If it's in good shape they should be able to epoxy it and turn it smooth easily.

I had a throat plate screw vanish during a blade change one time. I gave up looking, assuming it dropped from the table and found a crevice in the garage. I few days later my router found it for me. It had rolled and fallen into the accesory table mounted router, straight into the motor housing. It did a number on the brushes but that was all (aside from alot of racket). A little emery cloth and new brushes fixed it right up.

[pierhogunn]

well, it's done, the motor does not go any more when you apply current to it. I got my last little bit of use out of it and now, it's done...

so sad

[Tom Slick]

Your commutator came apart. those copper bars are epoxied onto the shaft and at least one let loose. I've had that happen on a circular saw before. the motor is a paperweight now.

[LCHIEN]

...
any thoughts as to what I may have done to screw up my beloved saw?

Almost all motor problems can be traced to excessive heat at some point.
Insualtion breaks down and wires short out, epoxies break down, wires melt, bearings seize, etc.

In turn, excessive heat is caused by too much current - the current causes Resistive heating - too much current in wires designed for less, and saturating the magnetics instead of inducing more force between the rotor and ths stator the eddy currents just short circuit internally in the core and overheat. The motor valiantly tries to pull more current to counter these bad things and do its work and spirals out of control.

If the motor starts laboring (slows down significantly) under too much load, you might still save it by backing off, letting it cool.
If you start seeing blue sparks and smelling insulation burning, it's too late, damage is done.

[pelligrini]

well, it's done, the motor does not go any more when you apply current to it. I got my last little bit of use out of it and now, it's done...

so sad

I saw a BT3000 motor, switch & misc parts in a recent ebay listing today.