Dying Motor on Sears Table Saw?

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Too little information to really diagnose positively, but electric motors don't usually "wear out" slowly. When they fail, it's more in the nature of sudden, catastrophic, and terminal.
The bearings might give out slowly, but normally you would have fairly obvious symptoms which you have not reported, mainly noise or a rough or gritty feel when turning the arbor by hand (unplugged! of course).
Given that the motor is likely no more than a 1 HP (typical for a home contractor type saw, even if it is a Sears and says more), and even wired for 120V and even run on a 15A circuit, it isn't likely to be tripping breakers with normal operation unless something else is going on (like additional load on the circuit--dust collection--or bogging down on cuts a lot, etc.). But again, not enough information.
My first suspicion would be dust, especially after 20 years of use. I'd check the on/off switch, the centrifugal switch, even the capacitor. Blow it out thoroughly with compressed air and see how it does.
Although the breaker might be the problem, and it's worth replacing for relatively few dollars, if you want to try it, they don't usually lose their effectiveness with just a few dozen trips--hundreds, maybe. What's your realistic trip count?
Here's a tip from troubleshooting 101: have you added anything to the circuit that didn't used to be there, like a dust collector? It's easy to forget conditions that have changed since the last known trouble-free period. In any event, what else is on the circuit?
As easy as that motor is to dismount from the saw, try taking it to a motor shop and get a diagnosis from them. Might cost you $30 or so, but you'll have a far more definitive answer than you'll get here.
--
LRod

Master Woodbutcher and seasoned termite
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Take the motor outdoors. Spray the berrings with trichlor, or some other solvent. Brake cleaner is OK.
Let it dry a few minutes, oil the berrings with zoom spout turbine oil. Two cycle mixing oil is OK if you can't find zoom spout. But the little bottles make life a lot easier.
Let the flammable solvent dry out completely. reassemble, should work better.
--

Christopher A. Young
You can't shout down a troll.
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turn off the suspicious breaker. plug saw into a different working circuit. does its breaker behave? is cord or plug overheating in use? is cord brittle or in need of replacement for any reason? examine suspicious outlet. are plug prongs loose or held firmly as new? after replacing suspicious outlet receptacle, plug a 1500 watt electric heater into the suspicious circuit and reset it, and try the heater. if circuit behaves, try saw. if saw or heater trips only the suspicious breaker, replace breaker.
Michael wrote:

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you could check actual current use with a clamp in ampmeter
harbor freight has them for under 20 bucks very useful around the home
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