Hum but no motion

Things do go pear-shaped in threes: Today I was happily mangling a piece of wood on my wood-lathe when sharpening became necessary. I turned on my smaller bench grinder which has a sharpening jig attached. The motor started to hum but the spindle would not turn. I switched off and turned the wheel by hand. Smooth as you like. I repeated the procedure three times with the same result. Possibly a little twitch of the wheel. I assumed the grinder was gone (Canadian Tire Jobmate, about two years old and hardly overused. Shame, I actually liked it more than my other grinder - way quieter). At the end of the session I tried to turn it on once more and lo and behold, it worked fine! I quickly sharpened all there was to be sharpened before I switched off.

So the question is: What is the likely cause of this intermittent fault?


Reply to
Michael Koblic
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Dirty start winding contacts. If you pull it apart, you'll probably find a spider-like device on one end of the shaft. It snaps out when the rotor gets up to speed and by snapping out, it disconnects the start winding contacts on the frame. Look for the start contacts and see if they are burned/corroded/dirty and fix them.

Reply to
Jim Stewart

Almost certainly true. But be careful when pulling it apart - bending the spider's legs will put it out of adjustment. In which case the contacts may never close or never open.


Reply to
Bob Engelhardt

  1. Bad switch
  2. Marginal connections to start cap
  3. dirty inboard startup switch

  1. Bad outlet.

If it happens again..check #4 first..then work your way down the list


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Reply to
Gunner Asch

agree - wood dust from your lathe and sanding - you could try compressed air to blow the dust out first, that might work - if it doesn't, take it apart and burnish the contacts with 600 paper and reassemble. Also make sure the centrifugal mechanism that actuates it moves freely.

If it happens aga>> Things do go pear-shaped in threes: Today I was happily mangling a piece

Reply to
Bill Noble

That reminds me of the homemade wood lathe someone gave me when I was in high school. It had the only electric motor in town with a rope starter. You had to make sure the rope was completely unwound and clear before throwing the switch.

Reply to
Ed Huntress

"Bill Noble" wrote in news:hddgda$o8n$

It's been so long I can't remember where it was, but someplace I frequented (friends shop?) had a grinder like this. You got used to giving the wheel a flick before hitting the switch, and off it went. Fixing it properly had been on his "to do" list for years, but the time it took to flick it into motion seemed so trivial compared to the time to tear it down & fix it that the owner never bothered. It's probably still like that if he's still around.

Doug White

Reply to
Doug White

I'd try burnishing with a crisp dollar bill held between the contacts first.


Reply to

Similar to a friend's printing press - flip the switch and roll the big flywheel. I seriously doubt that the little 1/4 HP washing machine motor could have got that thing rolling from dead stop even with the start winding helping! Gerry :-)} London, Canada

Reply to
Gerald Miller

I have a buffer like that. 2 HP, 120V 3450 RPM single phase motor. It actually can self-start, but when doing so it draws peak current of

195 amps for part of a second. Sometimes the 20 amp breaker can ignore that, sometimes it can't. I just give the wheel a brisk spin before hitting the green button.
Reply to
Don Foreman

I think you just answered your own question - The little motor couldn't get it rolling from a dead stop. Without the start winding you have to get a motor spinning pretty fast for the Run winding alone to get it moving, and that with no load like a radial arm saw.

I think the little Chief 15's came with a 3/4 HP motor. When I was young and foolish I thought they were overpowered for what they were, then I sat down and thought about it.

With the large flywheel mass and all the friction points on an offset press (all the damper rollers and ink system rollers, the friction caused by the blanket, the in-feed and out-feed mechanisms, etc.) all being run by that one motor, 1/4 HP wouldn't have a chance without a hand-spin.

Go ask the friend - Betcha the old motor died, and he had that little one on hand. And "it worked" so he never bothered.


Reply to
Bruce L. Bergman

Bad capacitor, sounds like, from here.

Reply to
Stormin Mormon

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