Rage mitre/chop-saw burnout repair

Seb Palmer · 5 Apr 2018

Hi, I have a Rage mitre/chop-saw. Whilst working on a project recently it started sparking a lot, followed by a burning smell, followed by total mechanical failure.

I've watched numerous videos on YouTube of people dismantling similar sorts of saws and repairing or servicing them, and have attempted to do likewise. Unsuccessfully.

I was able to remove the brushes, and reckon I need new ones. But I've been unable to either get the motor itself out, or even to get access to it to clean/repair it. Any hints or tips?

Thanks, Sebastian

PS - I'd like to suggest that there should be a repair/maintenance section under the 'Tools' area of the forum. My most common posts and my predominant interest here on UKW so far is Tool maintenance/repair, which comes under neither the 'buying advice' or 'review' categories as things currently stand.

Eric The Viking · 5 Apr 2018

My expectation is commutator damage.

If you had continued to try to use the saw once the big sparking started you might have done irreprable damage to the commutator - the arcing will have scored the surfaces and probably also pitted the trailing edges of each plate, the degree depending on what exactly happened.

If you can dismantle the back of the motor, you might be ale to check the commutator: Smoothness and concentricity are the key things. it might be possible to fettle it, using fine wet+dry (used dry and frequently cleaned), and scrupulously cleaning up the filings, but whilst older & bigger motors (and dynamos) were intended to be skimmed occasionally, cheap ones usually don't have enough meat to do this, and anyway it changes the geometry, so it doesn't work well with small diameter commutators. Skimming properly is done on a lathe. People who service motors do this, but that sort of saw is probably not easily dismantled to enable that.

So, if the issues go beyond the brushes, you may struggle to make a good repair. You ought to be able to get brushes cheaply*, so I'd fit some and see. If it's going to run again, it will probably start up sparking a bit but quickly settle down. If it doesn't settle, the commutator itself is scored, probably too badly to be repaired. If the latter, you might keep it running roughly, but the brush and commutator wear will be a lot faster, and power will be down to some extent.

It's probably worth changing any spark-suppression capacitors at the same time (it's possible one of those failed, causing the initial arcing).

IF the commutator isn't too nasty and you suspect a bearing, check this without the brushes in place (and obviously without the mains plug in any socket). Rotate the saw and listen and feel for any grinding or slop (sideways or axially). The most-likely-to-be-damaged one is the big bearing next to the blade. The least likely is probably the one at the end of the motor by the commutator, unless the saw has been used in a very dusty/gritty atmosphere (it's usually not well protected as air has to move around the brushes). Universal motors (like that one) usually have a gearbox between the motor and the shaft driving the blade - it's possible a bearing has gone on an intermediate shaft, but less likely than the man blade shaft or the back of the motor. They're also a pig to dismantle and reassemble (the Elu/DeWalt ones have a wide belt system which is horrid, but they are very reliable and accurate).

It's just possible that the motor ingested something metal, which cut into the windings somewhere. They need considerable airflow nowadays, for cooling, so the velocity is quite fast inside the motor, and the winding insulation is only a modern varnish. I've slipped with a bladed screwdriver and done it.

E.
PS: there are far more experienced "motor" people around the forum, to whom I happily defer.
*Ebay or a motor repairer local to you (take the old ones!).

Racers · 5 Apr 2018

I reckon a shorted winding on the motor, I have had the same thing a few times, do you have a meter to check the resistance of the windings?

Pete

Seb Palmer · 6 Apr 2018

Thanks Eric. Thanks Pete. I'll explore your suggestions. If it turns out to shorted windings, is that a relatively easy repair job?

Whilst I'll admit I'm actually unsure what caused the problem, I think it may have arisen due to my relatively new workshop not having any form of dust collection... as yet

dzj · 6 Apr 2018

Remove brushes and see if you can inspect the commutator.
Sometimes a bar falls off or is damaged in some way. That would
account for the sparking and smell.
There's no cheap fix for this, but at least you'll know where you stand.

Racers · 6 Apr 2018

Seb Palmer":3pdsure6 said:
Thanks Eric. Thanks Pete. I'll explore your suggestions. If it turns out to shorted windings, is that a relatively easy repair job?

Whilst I'll admit I'm actually unsure what caused the problem, I think it may have arisen due to my relatively new workshop not having any form of dust collection... as yet

You will need a new rotor if it has shorts.

Pete

Seb Palmer · 11 Apr 2018

Well, I ordered new brushes, which arrived today. Fitted them, and the saw is at least working. But there's still a lot of sparking and a strong burning smell. Will that disappear with use, or do I need to continue diagnosis/repairs?