Hi guys. I’ve run into a problem with my table saw that I need some help troubleshooting. I’ve had the saw (a Craftsman 2-HP hybrid) for a little more than 2.5 years and haven’t ever had this problem before. I had used the saw quite a bit yesterday and, frankly, a ton over the last 6 weeks with no problem at all. Toward the end of the day, I had 2 more cuts to make and when I went to turn the saw on, it went “buzzzzz” and the blade started turning slowly but wasn’t picking up speed. On the rare occasion in the past when this would happen, I would turn off the saw and then turn off the other electrical devices on that same breaker circuit, and then it wouldn’t be a problem; obviously the problem at that point was too many amps on a hot wire.
Last night, though, it was different. After doing the same thing as when I would otherwise run into this problem, I turned on the saw, and still no movement. I figured that it being late and me being tired, I’d let everything rest overnight and tackle the problem fresh this morning.
Unfortunately, the saw didn’t fix itself overnight, so I know that hot wires aren’t the problem. The blade isn’t bound up on anything, as it spins freely by hand. The belt is in good condition and properly tight and there’s no interference with anything in the path of the belt, arbor, or blade. The cabinet was very full, so I vacuumed that out first and tried again, still no luck. Without removing the saw motor from the cabinet, after unplugging the saw, I pulled off the side cover of the motor so that I could see the armature and it was very, very dusty (despite this having a TEFC motor). So I blew it off with compressed air (~50 psi) and vacuumed that too. Reassembled and replugged everything, same result: no spinning blade. When I turn it on, the motor makes a loud buzzing sound like it always does at the start, but then it doesn’t start spinning like usual.
Any thoughts on this problem & the cure? Do I need to pull the motor out and disassemble to blow out the rest of the dust, then re-assemble and see if that fixes everything? Or am I looking at a new motor? Thanks in advance guys.
Pat
Replies
Sounds like your start windings aren't kicking in. There's a centrifugal activated switch that is closed when the motor is stopped, and energizes the "start windings" that give the extra "oomph" to get the motor started when power is applied. Then as the motor comes up to speed, a centrifugal weight arrangement opens the switch, and the start windings are disconnected and the run windings take over to power the motor.
That switch, or rather the contacts for that switch, may be dirty or corroded. You may have to disassemble the motor to get to the switch, or if it is not an enclosed switch, you may be able to blow it out throught the vents. If it is an enclosed switch, you may not be able to blow it out and will have to get another one. In either case, the switch is mounted on one end of the motor, so the centrifugal weight arrangement can activate the switch. If the switch is burned out, or you can't get into it to blow it out, you can probably get a new one from Sears, or the motor mfg, or anyplace that sells and/or services electric motors.
Another possibility is a bad start capacitor, but I'd check the switch first.
Lots of luck
GT
I had this problem with a jointer motor several years ago. I solved it finally by placing a sheet metal deflector over the motor so as to direct shavings and dust away from it. To get it going after a good cleaning, I sometimes had to use emery cloth on the contacts.
GT,
I was just reading your post to the gentleman whose motor wouldn't start. Ironically, immediately after I returned to my shop I discovered the motor on my lathe wouldn't start. Or, rather, it would try to start and would spin slowly but would never make it past maybe 20-30 RPMs.
So, with what you said in your post in mind, I disassembled the motor and found the contacts you spoke about in the centrifigal switch. They were quite corroded. I ran a little micro file in there and brightened them up. While I had the motor apart I blew everything out with compressed air, and then reassembled it.
With everything back in place I hit the switch and the motor started up like a champ. Miraculous!
So, thanks a million for your advice. I didn't want to have to bring this motor down to the local service place and wait a week for them to even analyze it. You saved me a bunch of hassle. Thank you.
Zolton* Some people say I have a problem because I drink hydraulic brake fluid. But I can stop any time I want.
Zolton,
Some people say I have a problem because I drink hydraulic brake fluid. But I can stop any time I want.
I just spit coffee all over by desk reading that! Too funny.
Regards,Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
Bob,
Thanks. A lot of people don't get the nuances of that one... Zolton* Some people say I have a problem because I drink hydraulic brake fluid. But I can stop any time I want.
As the last poster said it could be the windings, but I would also put a meter on the outlet and make sure your getting the right current. I had a similar problem once, and one of my power lugs was not down secure at the panel. I was not getting good current at the outlet. It gave a similar symptom. After I tighented down the lug, and checked the power at the outlet, she fired right up. Just something to try before blaming the motor. (although odds are that it is not because of power, I just try to eliminate the obvious).
If it moves, tax it. If it keeps moving, regulate it.
And if it stops moving, subsidize it.
I agree that the easiest thing to check is the voltage, but there is a way to verify that the starter winding are the culpret.
Raise the blade to full height. Then, with a piece of scrap wood, spin the blade towards you. While the blade's still spinning (and you're all clear) turn the saw on. If the saw comes up to speed to your satisfaction, then the starter windings are probably clogged with dust or is burned out.
This happened on an old saw of mine and was easily fixed by a retired motor repair guy who lives nearby. (wouldn't it be nice everyone had just such a gem in the neighborhood?) Luckily my problem was only due to dust.
Good luck, Mark
Hey guys, thanks for all the great tips!
Here’s the conclusion to the story. Last night I removed the outer cover, the external fan, the inner shroud, and then pulled out the spring-loaded centrifugal switch, which looked and operated pretty much as I would imagine that it did the day it left the factory. But, since I had it out I passed some sandpaper over the contacts although they didn’t look like they needed it at all. Same thing on the other part of the switch. Made sure that all the screws were tight (they were), blew it all off with compressed air again, then re-assembled everything. Forgot to put the fan back in somehow until I had the outside all buttoned up—Doh! So I had to take that outer cover off again, fan on, cover back on. Decided to hit the motor with the meaty part of my fist a couple of times since that sometimes seemed to work on the old Mustang I drove in high school.
Closed the cabinet back up, cleared the top of tools, plugged the saw in and hit the green Start button. Eureka! Started just like the day it was brand new. I couldn’t believe my eyes (or ears) because after I found everything shiny and new looking inside, I was convinced that I was going to have to remove the capacitors. Turned it off, let it slow to a stop, then started it up again just to see if the electrical gremlins were just playing games with me. I guess maybe leaving the side door of the saw cabinet open all day was enough temptation for them to leave my saw, because it started up again and cut just fine.
So, I’ll be darned if I know what was really wrong. What I did shouldn’t have had anything to do with fixing it, except maybe banging the motor with my hand if there was a short somewhere? But I guess so long as it’s working, I’m not going to go looking that gift horse in the mouth.
Thanks again to everybody for jumping in to help me out on this one. I didn’t know where to start and now it’s working again, which means I’m working again. Cheers.
"I don't know what's wrong with it."
"Take it apart and have a look."
"I don't believe it. I took it all apart, nothing caught my eye as being the problem. I put it back together and..."
"It works fine. Yup, had it happen lots of times. You gotta show these things a bit of love now and again." ;-)
This same thing would happen with the sears Radial arm saw. On mine the "switch" would move on the shaft to the point the weights were away from the contacts and do just what your motor did. Sears guy wanted to sell me a new motor, but pushing the switch back does the trick.
You know, it looked like that might have happened on the shaft of this motor too. There was some scuffing where the set screw held the centrifugal weight part of the switch to the shaft, and I'm sure I moved it more inboard when I put it all back together. I know I'm showing my ignorance in regard to motor design/construction, but wouldn't that merely have prevented the switch from kicking over from the capacitor-start to regular running power?
Its all done with magnetic fields. The capacitor causes a 90 degree out of phase condition and this make the rotor attempt to re-aline. As the speed builds the rotor magnetic field never catches the stator magnetic field and the contacts "switch" and the capacitor is no longer needed.
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