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Old 16th Jun 2021, 5:04 am   #1
Martijnvanhooff
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Default Restoring a old table grinder

Hi all,

I am currently restoring an old Metabo.
Approximately the same as the one I uploaded.
While dissembling, I found that 2 wires of the magnetic coil were broken.
The grinder worked before dissembling, but I don't know if it broke during dissembly.

Is it still a nice project to continue of did I it up?

Thanks
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Old 16th Jun 2021, 6:15 am   #2
FIXITNOW
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Default Re: Restoring a old table grinder

Nice project just had to repair my compressor where the wires to the start cap and the mains in had their insulation breaking down. So worth putting new power cable in while it's apart.
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Old 16th Jun 2021, 7:02 am   #3
Martijnvanhooff
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Default Re: Restoring a old table grinder

I will, same happened here haha. But do you think it is working with 2 of the wires in the coil broken?
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Old 16th Jun 2021, 8:21 am   #4
mark_in_manc
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Default Re: Restoring a old table grinder

I don't want to be a voice of gloom, but the windings look a bit burned in your picture. What does it smell like? Perhaps measure continuity across the windings - if there is none, you know it broke as you took it apart (that sounds like my 14-yr-old-self - 'it just broke, Dad' ). Induction motors are on my mind at the moment - I don't think the grinders I use here have a centrifugal start-run switch, so you may have a start-winding with a capacitor on it, assuming this is single-phase. If it is 3-phase, perhaps it will run with one phase broken, but it would perhaps hum quite a lot!

It is difficult to repair things like this where the motor fits into a casing, and a general-purpose motor is hard to fit. If this one is no good and spares cannot be found, I wonder if you can drive the rotor from an external motor using a belt. But this is getting a bit OT for this forum and involves brutality with an angle grinder
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Old 16th Jun 2021, 9:41 am   #5
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Default Re: Restoring a old table grinder

That is a start/run type motor!! It will have a centrifugal switch. The start winding is cooked.
This happens when "some people" want 40 horsepower out of a 1/2 horsepower motor.
It is repairable!!, and its quite easy. BUT unless you have rewound a motor before it's not worth the time or money.

Sorry :-(

Joe
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Old 16th Jun 2021, 12:04 pm   #6
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Default Re: Restoring a old table grinder

That is a very, very nice pedestal grinder. If there is no other alternative, it is worth sending the motor out to a professional rewinding firm and paying to have it done. You just can't buy tools of that quality new any longer.

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Old 16th Jun 2021, 9:28 pm   #7
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Default Re: Restoring a old table grinder

If you take David's advice, it would definitely pay you to replace the bearings as well. With a little care it will last another lifetime.

Joe
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Old 17th Jun 2021, 8:21 pm   #8
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Default Re: Restoring a old table grinder

If it was mine I would opt to have the motor rewound professionally as well as get it fitted with new bearings.

Joe
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Old 17th Jun 2021, 8:54 pm   #9
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Default Re: Restoring a old table grinder

Since the starting torque requirements of a grinder are so small I would expect it to be a single capacitor start/run motor with no centrifugal switch; the capacitor feeds the auxiliary winding all the time. If the auxiliary winding is cooked then I would suspect that the capacitor has failed short/leaky. If it is the main winding which is cooked then I would imagine that someone tried starting it with the rotor jammed somehow, and it wasn't switched off in time.
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Old 18th Jun 2021, 8:09 am   #10
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Default Re: Restoring a old table grinder

in this neck of the woods a motor rewind is only viable if you can get a friend to do it for you, commercially it'll cost more than a similar used grinder at the auction.
Our single phase one at home is centrifugal switch start, the one at work is 3-phase and direct-online
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Old 18th Jun 2021, 1:19 pm   #11
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Default Re: Restoring a old table grinder

That burnt winding is /was the start winding and the motor is single phase. As there is no load on the grinder on start up, so a capacitor wasn't needed or fitted. The same pedestal was used on 3 phase motors. As Kevin above says, it is costly to have a motor rewound. If you are brave you can wind a length of cord around one of the spindles and give it a pull then quickly switch the supply, over the top way first. A bit doggy, so be very careful. Perhaps the moderator might delete. ted
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Old 18th Jun 2021, 2:40 pm   #12
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Default Re: Restoring a old table grinder

The motor does look to have well-toasted itself, in which case you'll find that the cost of a professional rewind will easily exceed the cost of a new grinder from the likes of Machine Mart or Toolstation - which will also come with modern-standard safety guards etc [which look conspicuously absent from your old grinder].
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Old 18th Jun 2021, 3:34 pm   #13
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Default Re: Restoring a old table grinder

Machine mart and toolstation don't flog grinders of that quality.

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Old 18th Jun 2021, 3:42 pm   #14
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Default Re: Restoring a old table grinder

The windings look quite like my small bench top grinder motors', one set of full sized windings for run and the other (the burnt out one) of very thin wire to give enough of a phase shift to get it going round. This works well with the beforementioned low starting torque required. I like the "pull start" idea.
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Old 18th Jun 2021, 3:47 pm   #15
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Default Re: Restoring a old table grinder

Quote:
Originally Posted by Radio Wrangler View Post
Machine mart and toolstation don't flog grinders of that quality.
But they do flog grinders that work, and are compliant with the current HSE guidance on the use of abrasive wheels.

[I'm a bit obsessive about the latter: a family member has only about 10% remaining vision in one eye following an incident with an inadequately-shielded bench grinder]
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Old 18th Jun 2021, 4:37 pm   #16
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Default Re: Restoring a old table grinder

I was working about 25 feet away from a large, high-speed surface grinder where someone had forgotten to turn the magnetic chuck on. The wheel exploded and the workpiece went flying, right through a 'Colt' heater hanging from the roof.

Let's say I learned a lot that afternoon and HSE guidance is a minimum standard. So, start with a good grinder and add good guards.... then wear personal protection as well.

You needed to be licenced to fit or balance grinding wheels for those surface speeds, and that was part of the training. It also wasn't a cheapie wheel that went off.

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Old 18th Jun 2021, 5:29 pm   #17
trsomian
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Default Re: Restoring a old table grinder

I doubt you would need a piece of string, just flick the wheels in the required direction, then switch on whilst they are still moving. Works fine on a fan motor I have. Would the failed start winding need removing, because it may have shorted turns?
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Old 18th Jun 2021, 5:58 pm   #18
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Default Re: Restoring a old table grinder

Quote:
Originally Posted by trsomian View Post
I doubt you would need a piece of string, just flick the wheels in the required direction, then switch on whilst they are still moving. Works fine on a fan motor I have. Would the failed start winding need removing, because it may have shorted turns?
If you can "just flick the wheel in the required direction" the machine has criminally-deficient safety guards/interlocks.

You only get one set of hands/eyes. __PLEASE__ play-safe when using industrial power-tools.
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Old 19th Jun 2021, 4:08 pm   #19
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Default Re: Restoring a old table grinder

Agree with the previous people - that winding looks fried to the proverbial! If it was me I'd get it professionaly rewound and new bearings as it looks to be a nice unit. I tend to think more in terms of quality than economics ie is it a good unit initially/worth rewinding is the main idea and the cost secondary (which is why I spent about 4 hours and about $20 repairing an analogue 'Weston' brand multimeter once when $10 would have easily bought me a modern better spec'd el cheapo). You are not going to get a new one of comparable quality and any cheap used one may be equally fried up (always suspect immaculate looking or cheap used gear for that reason!!). So go for it.
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Old 21st Jun 2021, 11:36 am   #20
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Default Re: Restoring a old table grinder

If you're quoted less than 400 for the rewind, you're doing well.
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