Craftsman Jointer motor hums but doesn't spin

[mikaho]

I bought a used craftsman 6" jointer. Ran fine for a few times but this past week I ran one board through it fine and turned it off for a minute. When I tried to turn it on again, the motor hums but does not spin. The motor and the blade assembly spin freely by hand. I took the motor off the jointer and tried it and it started up fine. I put it back on the jointer and again, it hums but does not spin. Even if I give it a spin by hand it won't kick on.

 

I've read that single phase motors have a capacitor on the motor that can go bad and cause this behavior. Everything I read seemed to say the capacitor would be under a cover on the outside of the motor but there is nothing on the outside of this motor. Pictures of the motor attached along with the switch and relay.

 

Craftsman 6" jointer 113.232210

 

Any ideas would be appreciated.

 

Michael

[paulengr]

I don't see a capacitor in your photos. The capacitor does not have to be on the motor itself. That's more of a pump/appliance thing. There are a couple components to look for. First in almost all cases the motor has three wires and two stator coils, a run coil and a start coil if it's a nonreversing motor. The coils share one of the three wires. Locate the wires and use an ohm meter on them. You should get 3 different readings. Direction doesn't matter. So start with the highest reading. This means the third wire is the shared one. This reading should be pretty close to the sum of the other two. The middle reading should be roughly twice the smallest reading. If you read open or shorted (less than 1 ohm) the motor is fried and needs replacement.

Moving on next you can have 0, 1, or 2 capacitors depending on the design. 120/240 V is single phase so without another phase the motor is not self starting. So the motor might be shaded pole and only have two wires but those are really inefficient so not on a planer. Second is it might have permanent caps but they might be hidden inside. With both caps the first one is a run capacitor. This increases the voltage and power to the motor. Not a necessity but most have one. It will be in parallel with the run leads (smallest resistance). Second is a starting capacitor that is in parallel with the start winding (middle resistance). These are bigger and contain a can filled with a roll of paper and aluminum foil soaked in an electrolyte such as glycol. It has a very distinct odor. The can is crimped shut. When the electrolyte dries out (roughly 10 years) or if the motor doesn't start after about 30 seconds or so (run caps are huge so they are thermally limited to reduce size) the capacitor overheats, the electrolyte boils, and the steam blows up the capacitor. This is what happens 95% of the time. There are two ways motor running is detected. Method one more common on cheap motors uses an inertia switch which is what it sounds like. A spring loaded switch hugs the motor shaft. Once it starts spinning a weight on the shaft pushes a lever to open the switch. These either get fouled or wear out pretty easy. Or thers is a voltage sensor that opens once the motor turns and the voltage across the start coil drops. This is called a potential relay. Much more reliable but they still go bad. If either type is present and they fail the start cap blows out too.

Except the inertial switch this can all be inside or outside the motor housing. If it's inside you'll have to pull the end caps off. If you do the bearings are pressed in so often this destroys the bearings. In the motor shop we just replace them anyways.

Plus if you can't tell this is all leading towards the fact that if it's something simple and obvious to test and replace, do that. But otherwise the cost and time of troubleshooting and sourcing parts often exceeds the cost of the planer itself or retrofitting another motor.

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