Table Saw Woes

[Herman Trivilino]

Last night I was making another pair of the HK-50 jigs from that same piece of oak that I used the day before to make a pair.  I wanted to do it while I still had the table saw out as my shop does double duty as a garage and when both cars are in there the table saw is rolled off to the side, covered up, and used as a platform for my Tormek.  (I found a way to keep this post on topic!) 

Link to table saw literature: http://www.mikestools.com/download/DeltaTableSawManuals/34-670.pdf

I made a cut, then when I went to switch it on to make another cut there was nothing.  I checked that it was still plugged in to a powered source.  So, I flipped it over and checked the switches.  Both were good.  I hooked it back up and it worked.  So. I flipped it back upright.  Then it didn't work, then it did.  One time I had to give it a spin to get it started.  I noticed a lot of sparks flying out of the motor towards the blade.  So I took the blade off, blew compressed air into the motor housing, put a blade back in it and was able to finish up my work.  This morning I made the final cross cuts that turn the single piece into two jigs and finished them up.

I flipped the table saw over again, but this time onto a pair of saw horses so I wouldn't have to work on the floor.  I took the base off, and removed the motor.  I took the fan pulley housing off and removed the brushes.  I blew compressed air into the motor from both sides and also through the two holes where the brushes go.  Put the brushes back in and bench tested the motor.  No more sparks.  Blew some more compressed air into it while it was running.

Link to motor literature: http://www.ereplacementparts.com/delta-34670-type-inch-table-saw-parts-c-3275_3334_7069.html

I wanted to replace the brushes so I went searching in vain for them at Lowe's, Home Depot, and Sears Hardware.  I looked at photographs of the replacement brushes on the web and they don't look much longer than the ones I have. 

Link to brushes:  http://www.ereplacementparts.com/brush-sold-individually-p-57904.html

So, I used this opportunity to clean and lubricate all the linkages that adjust the blade height and miter angle, put it all back together and I think I'm good to go. 

Could it be the sparking was due to an accumulation of dust inside the motor?  Back in the day when I was a carpenter and doing trim work (2nd fix) the boss regularly cleaned his table saw motors by blowing compressed air into them while they were spinning.  It's not safe to do that to this saw unless you've got the saw upside down, so I never did it.  I did blow the dust out on occasion, but not while the motor's running. and not in recent memory.

[Mike Fairleigh]

Very odd problem.  What condition were the brushes in when you took them out?  How much of them were left?  Did a lot of debris come out with the compressed air?  My initial thought is either worn or shorted brushes and/or brush springs, or a worn out or defective commutator in the motor (which I would think unlikely, but would probably mean replacing the motor if that turned out to be the problem).  Brushes have been known to stop working reliably when they still had quite a bit of length left, so it would be worth just putting in a new set and seeing how it goes.

But I'm no expert with non-induction AC motors (or anything else made by Man, but I'm more familiar with induction motors), so that's just my wild guess based on having rebuilt DC starters and alternators in the past.

[Herman Trivilino]

Very odd problem.  What condition were the brushes in when you took them out?  How much of them were left?  Did a lot of debris come out with the compressed air? 

The brushes were uneven in length, one was a bit more than half it's original length, the other a bit longer than that.  They had grooves worn in them.  A lot of dust came out.  In recent years I've been building speaker cabinets so I cut a few sheets of MDF.  Really dusty stuff.

The thing is, it's running great now so maybe I should get a couple of brushes to have on hand.

Thanks, Mike.

[Mike Fairleigh]

I try to keep a spare brush set on hand for any tools that use them, since I've seen manufacturers discontinue them.  (Of course now I have a drawer full of brushes and I don't know what they go to...)  It may also have been that one or both of the brush springs were weak enough to allow some of that debris to get between the brush and the commutator, creating an intermittent connection.  It seems odd that Delta doesn't protect the motor a little better.  Glad its working again.

[Herman Trivilino]

While this table saw is definitely one level above the cheaper table saws meant for home owners, it's at the bottom of the contractor grade table saws.  Don't get me wrong, it has a beefy table and accurate blade control, but it is a direct drive. 

These motors have to breathe to stay cool, so they are exposed to the saw dust!

[Mike Fairleigh]

I have a Unisaw/52" Unifence which uses a true 3HP TEFC motor.  The tradeoff of course is that it fills my whole shop - to the point where I've toyed with the idea of selling it.  I'm a long way from pulling that trigger, but it has crossed my mind the more time I spend using hand tools.  It's on the Delta mobile base, but unless your shop is the size of a football field, you can only move a full sized cabinet saw with 52" fence so far.

I love Delta's line of contractor saws.  The original "Delta Contractor Saw" which was discontinued a number of years ago was the standard by which all saws in its class were judged.