Delta Motor Help

[wrench136]

What I have is: Delta Repulsion-Induction motor. 1/3 hp, type SR, cat, # U6400, 110/220V, 1725 RPM.
This is connected to a late 30s vintage table saw which I think is a model 34-160.
Problem is motor hums but does not start. Motor will start with belt off. I've taken the motor apart and cleaned the commutator of carbon back to copper. Same problem. Was thinking try new brushes next. There are 2 in this motor. Contacted Arrowhead Electric/Carbon Brush. They could not help me.
Specs on brushes are: EG over # 6749, .5" width, .183 thickness, .882 length (as is now). Maybe 1"new ? Wire comes off top beveled corner.
Any ideas where to find new brushes?

 

[RTM]

Start capacitor?

Blade spins easily without motor attached?

 

[micromind]

When it starts, can you see any sparks from where the brushes contact the commutator? There should always be sparks, even small ones.

Is the mica insulation between the copper bars higher than the copper? This will usually cause lots of sparks then burn up brushes quickly then when the brushes no longer contact the copper, failure to start. This is called 'high mica'. Very common.

Do the brush springs push the brushes into the commutator enough? Excessive sparking will weaken them.

If you can find brushes that are too big, they can be filed down to fit.

 

[wrench136]

Start capacitor?

Blade spins easily without motor attached?

No start cap. Blade spins easy without belt.

 

[The Cobbler]

unless your brushes are worn to the point they aren't contacting the comm firmly , I doubt that's your problem.
if they are not pressing firm that could be a problem.
good advice above from @micromind .

 

[Roberts210]

The R.I. motors work a little differently than ordinary capacitor start motors.
The guys at OWWM will know a lot more about how to get your motor up and running again.

 

[wrench136]

When it starts, can you see any sparks from where the brushes contact the commutator? There should always be sparks, even small ones.

Is the mica insulation between the copper bars higher than the copper? This will usually cause lots of sparks then burn up brushes quickly then when the brushes no longer contact the copper, failure to start. This is called 'high mica'. Very common.

Do the brush springs push the brushes into the commutator enough? Excessive sparking will weaken them.

If you can find brushes that are too big, they can be filed down to fit.

No sparks at all. Mica and copper are smooth.

 

[Cruzan80]

This may be your problem. Mica should be undercut from the copper, IIRC.