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Author Topic: Bench grinder problem  (Read 2509 times)

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Varche

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Bench grinder problem
« on: 17 December 2007, 13:50:17 »
Irritating problem.

I bought a twin wheel £15 bench grinder 4 years ago. Tried it once. It worked. Put it away and am using it in earnest now to sharpen hand tools etc..

Problem is it starts up and takes ages(minutes) to get up to speed. I keep expecting it to burn out!

Before I bin it and splash out 15 euros here on another identical one is there anything I could try to make it work better? Could it be a brushes problem or the commutator(?) with muck in the grooves?

varche
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Marks DTM Calib

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Re: Bench grinder problem
« Reply #1 on: 17 December 2007, 13:55:15 »
Often they are induction motors in order to get them to run at a near constant speed (1500 or 3000rpm).

These require a capacitor in order to get them to operate on a single phase setup.....and when these start to die, the motor power drops off very quickly....
« Last Edit: 17 December 2007, 13:55:33 by Mark »
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Kevin Wood

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Re: Bench grinder problem
« Reply #2 on: 17 December 2007, 14:00:12 »
Most likely it'll be an induction motor which means no brushes, etc. to worry about. You'll probably find it has a pair of stator windings which are phase-shifted by a capacitor, and it's the capacitor that's the most likely component failure, I'd say. It'll be running on a single stator winding at the moment, which is why it's a bit sluggish. You might also find it doesn't start reliably or will start in reverse if you flick it backwards as you switch it on.

If it's not the capacitor you might find it's got a speed sensitive switch which reduces the power of the motor as it reaches operating speed. This may have jammed open, reducing the starting torque.

My money's on the capacitor, though, so should be an easy fix :y

Kevin

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Kevin Wood

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Re: Bench grinder problem
« Reply #3 on: 17 December 2007, 14:01:28 »
D'oh! Must type faster. There you go.. 2 votes for the capacitor...
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Golfbuddy

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Re: Bench grinder problem
« Reply #4 on: 17 December 2007, 14:01:41 »
I couldn't agree more. Go and buy a new one. Bloody farmers.  :-X

 ;D ;D ;D
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Varche

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Re: Bench grinder problem
« Reply #5 on: 17 December 2007, 14:03:16 »
I will have a look. It is a 3000 rpm job.

Funnily enough we have 3 phase electric. Not for big load items , though our well pump is 3 phase, but to get enough potencia from the antiquated twisted bell cable public overhead distribution! (5.5Kw)

varche
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Kevin Wood

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Re: Bench grinder problem
« Reply #6 on: 17 December 2007, 14:05:02 »
Quote
(5.5Kw)

Enough for a few sets of Christmas tree lights [size=9]and not much else![/size]
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Marks DTM Calib

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Re: Bench grinder problem
« Reply #7 on: 17 December 2007, 14:09:34 »
Quote
I will have a look. It is a 3000 rpm job.

Funnily enough we have 3 phase electric. Not for big load items , though our well pump is 3 phase, but to get enough potencia from the antiquated twisted bell cable public overhead distribution! (5.5Kw)

varche

Trouble is that the single phase motors only have two seperate windings.....

.....and the cost of a new capacitor might be more than a new grinder.
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Danny

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Re: Bench grinder problem
« Reply #8 on: 17 December 2007, 14:20:44 »
isnt it obvious??

you bought it 4 years ago... its due a cambelt change!! ;D ;D
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Kevin Wood

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Re: Bench grinder problem
« Reply #9 on: 17 December 2007, 14:24:09 »
Quote
.....and the cost of a new capacitor might be more than a new grinder.

Very true. Picked up a combined 6" grinder and belt sander for 25 quid VAT free at Machine Mart.

Without belt sander it was 14 quid. Hardly worth changing the stones on them. In fact I know a few commercial users who just chuck them when they need replacing rather than risk having a wheel burst and be liable for installing it badly.

Kevin
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Markjay

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Re: Bench grinder problem
« Reply #10 on: 17 December 2007, 15:18:16 »
Why would you want to grind a bench in the first place?  :o




(I'll get my coat)  :-X
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Marks DTM Calib

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Re: Bench grinder problem
« Reply #11 on: 17 December 2007, 15:19:27 »
Quote
Why would you want to grind a bench in the first place?  :o




(I'll get my coat)  :-X

Thats a nasty case of jimbobitus....
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Markjay

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Re: Bench grinder problem
« Reply #12 on: 17 December 2007, 15:21:19 »
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Thats a nasty case of jimbobitus....

 ;D


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Varche

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Re: Bench grinder problem
« Reply #13 on: 17 December 2007, 15:47:48 »
Just removed sole plate. Breather all blocked up. oil in plug well. Hadn't noticed ABS light on before so bet that is the ECU gone. Worse there are bits of the gearbox thrust washer in the sump. :o

Put it back together and idle is all over the place despite using tons of carb cleaner on IAC. Tried getting it up to speed but misfiring so that might be the DIS pack. Bad vibration so looks like one of the wheels is out of balance.

Strange whine from front of engine. Could that be the belt tensioner pulley about to give up or secondary air valve!

Tried paperclip test but got electrocuted.  :o

Think I will buy a new one!
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Kevin Wood

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Re: Bench grinder problem
« Reply #14 on: 17 December 2007, 16:17:50 »
Quote
Tried paperclip test but got electrocuted.

That is a new one  :-/

Kevin
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