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Thread: Old bench grinder won't turn.
06-02-2012, 07:48 PM #1
Old bench grinder won't turn.
I'm new here (first post), so I'm hoping I put this thread in the right place...
I have an old Craftsman bench grinder and she seems to have given up the ghost. My father gave it to me, so I'd like to see it turn again. Its stamed Nov. 28 1968 on the baseplate and according to the faceplate it is a 1/3 horse motor that draws 3.5 amps at 115 volts. The wheels turn freely by hand, but under power it locks up and hums. It can still be turned by hand under power, but has considerably more resistance. From what I understand (which isn't much), these split phase motors are fairly simple. They consist of the motor itself, a starting relay, and a power switch. So, I've been trying to systematically determine where my trouble lies. I figure if I here a hum after flipping the switch, its getting power, so the switch is good. Then, I slapped a multimeter on the motor to check its resistance. My thinking is if I was getting next to no resistance, there may be a short somewhere in the windings. However, I'm getting something like 13 ohms. I didn't expect the resistance of a bunch of copper wire to be too high, so 13 ohms sounds reasonable to me. Also, if there was I short, I would expect the breaker to trip (which wasn't happening). So, this is telling me that it is the relay.
I've got a couple question for all of you. Is there any good method of testing a relay? If it turns out to be faulty, what are some viable replacements? I can imaging finding this specific of a relay (a Klixon 2CR-14-224) could cost me a pretty penny (probably more than a new grinder) so would there be some sort of generic replacement I could slap in there? Can you think of anything I am forgetting to test?
I appreciate the help in advance. I figure if anybody will know how to get it turning again, I'll be one of you. I've attached (hopefully) a few pictures below to give you a better idea what I'm taking about.
06-02-2012, 08:20 PM #2
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06-02-2012, 08:23 PM #3
Check on an electric motor forum but if the unit hums likley the capacitor is shot. If it is that its a cheap quick fix.
Check to see if you can get it to spin up if you give it a start at turning.
06-02-2012, 08:53 PM #4
It left the factory with neither of those items, and is not of a sort to benefit by their addiition.
On an El Cheapo split-phase grinder (AKA misplaced kitchen vent fan motor), the more common cause of the symptoms listed is that the thrust washers (thin brass and thicker black or brown phenolic, IIRC) are worn or have split into bits and fallen out.
Result? A motor that spins freely power OFF, pulls its armature toward one end and jams. A byproduct of the field and armature never being perfectly aligned, and the price-point to which it was built not having margin for proper bearings.
Test for that by powering-ON, then pressing a bit of wood against each end of the shaft in turn to see if it frees-up and starts to turn under power.
THEN have the POS bronzed... The typical Chinese-made $49 to $89 6" and 8" grinders one finds in 'Big Box' or online are really, really, poor excuses for grinders.
But they still outperform this one.
06-02-2012, 08:57 PM #5
06-02-2012, 09:31 PM #6
Bill, I can't quite tell, do you think this grinder is worth salvaging? Stuart, I looked up the part and that is what I saw...wasn't too promising but I didn't know if y'all would know of an inexpensive part I could swap out to press it back into service. I'm in college and I'm trying to scrape together enough to purchase an old lathe, just wanted to try and avoid buying another piece of equipment. Just for giggles, I'll put this thing back together and see if it is the thrust washers causing the problem.
06-02-2012, 09:41 PM #7
Open the motor and clean the contact on the starting switch. Check for a broken wire to the switch..
06-02-2012, 09:43 PM #8
Replaced by the physically larger and higher-amp 4CR, which is still available and a wire-in replacement if there is space for it.
And money. Though EPray could probably find one cheap enough.
But neither includes a capacitor as-listed, and the startup characteristics as I recall them (circa 1970-'74 when the sucker was pitched into the kitchen garbage) were not those of capacitor-start.
More akin to a 1950 Buick Dynaflow waddling slowly off the mark in high-range. One had to wait for it to get up any speed.
Unlke the Buick, it gave-up that speed the minute you started to grind anything much huskier than a Victrola needle.
Functional replacement at the time - a B&D portable belt sander clamped downside-up in a bench vise - did a far better job of hogging OR fine-edge grinding.
..and not to put too fine a point on it .. but this sort of time-wasting over junkbox trinkets is wot I/we shouldn't be wasting PM's resources on.
For my part, I'm going to shut up and go bake some fish for supper...
06-02-2012, 10:03 PM #9
Bill, didn't mean to waste "resources." Just looking for a little help, thats all. Didn't know enough about it to know if it was junk or not. Thats why I asked.
06-02-2012, 11:00 PM #10
Point is that young and struggling doesn't mean your time is free, or even plentiful. It might be some time before CASH comes your way per each hour - but that means that until it does you actually have LESS time to waste on unproductive effort than older folk - not more.
Whatever your goals are, that grinder isn't even a good start at learning about electric motors.
You need to scout for things to do that advance your goal - not necessarily all work, no play, either. But raising the mechanical dead should not be squandered on road-kill.
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