Craftsman table saw from the early 70's, motor hangs out the back and drives the blade via a belt.
Turn on the power and the motor hums, but won't 'start'. Wrap a string around the shaft opposite the pulley, pull, and the motor will come to life. Tried a new capacitor, didn't fix it. Now what?
I assume this is not a proper fix:
Capacitor was my First guess.
Next thing I'd be checking is the brushes and commutator, and whilst in there check any bearings/bushings are moving as freely as they should.
You plugged into a good solid plug? I've seen them not start properly when plugged into a long extension cord.
If looking at brushes etc, just get a new motor?
extention cord is 12ga, cord etc is good. Plug directly to wall outlet has same effect.
It depends on how you value your time I guess.
Brushes could be changed out in about an hour and as such are probably worth replacing. If the commutator or windings are damaged then yes, replacing the motor is probably far more economical.
If you are doing brushes, if you can't find the right size, you can go a little oversized and sand/file them down to suit.
Twenty years ago, I knew a small shop that would rewind and repair electric motors rather economically. I have no idea if such shops still exist.
I have an old pool filter left outside, same problem. Sprayed WD40 on everything, still using it today.
I would disconnect everything and make sure you don't have a tight bushing or bearing. Not much torque needed to start a saw, so there won't be much for startup windings in the motor.
Starting switch?
In reply to bentwrench :
Probably not with the switch in the on position it hums like the starting capacitor is shot. However he replaced it with another one.
My bandsaw does the same thing. I just prop start it and it runs fine.
In reply to Gearheadotaku :
Prop start it.
With the power switch off Give the blade a spin and while it’s still spinning flip on the switch. If it runs fine the problem is the starting capacitor.
On a single phase induction motor you have two elements that need to work properly for the motor to start. The capacitor and the centrifugal switch. Since you already replace the capacitor, the problem is most likely sawdust jamming the centrifugal switch. The centrifugal switch is located on one of the bearing supports, most likely on the rear bearing support.
What he said^, there aren't any brushes to deal with, just the centrifugal auto start switch (that click you hear right after one is shut off is the contacts snapping shut). I'm pretty sure you can check the contacts for continuity first to confirm that's the issue without taking it apart. JUST BE VERY CAREFUL WORKING WITH CAPACITORS, they typically discharge themselves, but it's a really bad assumption to make, always check for voltage.
As you can see, neither side of the (disconnected) cap should be open to line or neutral, that would indicate the switch isn't closed or a start winding has gone open.
so that switch is outside the motor?
No, it lives inside the motor, when the motor is below a certain RPM it's closed, it opens up when the motor is running to disconnect the start winding.
Pulling the end(s) off a motor and sliding out the rotor is really easy, but I don't like taking stuff apart if it doesn't need to happen, hence the suggestion of ohming it out first. Though really it pretty much has to be an issue in there and the bearings are probably about due to be replaced (or repacked if they aren't sealed) anyway.
In reply to BrokenYugo :
Thanks, now I have another thing to check on my problematic horizontal band saw! I'd replaced the start cap and replaced all the bearings save the two in the actual motor case (seems like everything turns pretty freely to me), and it starts *some* of the time, and hums others, subsequently tripping the built in thermal breaker. Gah. Facepalm: Also trips that even when it's started after a few seconds... usually.
The centrifugal switch seems to work quite nicely when it does start, and I've been careful about making sure the connection is made and broken completely in the two positions.
I'm super-bummed that Grizzly decided to make the end plate opposite the fan integral to the gearcase on this one. It's a lot to drag around to repair shops.
Apologies to the OP for the threadjack, but it's so dang parallel... 
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