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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details. |
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16th Jun 2021, 6:04 am | #1 |
Diode
Join Date: May 2021
Location: Eindhoven. Netherlands.
Posts: 7
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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 |
16th Jun 2021, 7:15 am | #2 |
Octode
Join Date: Feb 2007
Location: Ely, Cambridgeshire, UK.
Posts: 1,975
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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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16th Jun 2021, 8:02 am | #3 |
Diode
Join Date: May 2021
Location: Eindhoven. Netherlands.
Posts: 7
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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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16th Jun 2021, 9:21 am | #4 |
Octode
Join Date: Nov 2011
Location: Manchester, UK.
Posts: 1,874
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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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16th Jun 2021, 10:41 am | #5 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
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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 |
16th Jun 2021, 1:04 pm | #6 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,867
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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.
David
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16th Jun 2021, 10:28 pm | #7 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
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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 |
17th Jun 2021, 9:21 pm | #8 |
Hexode
Join Date: Dec 2019
Location: Hohenroda, Eastern Hesse, Germany
Posts: 460
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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 |
17th Jun 2021, 9:54 pm | #9 |
Hexode
Join Date: Oct 2010
Location: Box End, Beds. UK.
Posts: 271
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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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18th Jun 2021, 9:09 am | #10 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,270
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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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Kevin |
18th Jun 2021, 2:19 pm | #11 |
Heptode
Join Date: Nov 2009
Location: Scarborough, North Yorkshire, UK.
Posts: 510
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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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18th Jun 2021, 3:40 pm | #12 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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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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18th Jun 2021, 4:34 pm | #13 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,867
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Re: Restoring a old table grinder
Machine mart and toolstation don't flog grinders of that quality.
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
18th Jun 2021, 4:42 pm | #14 |
Guest
Posts: n/a
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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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18th Jun 2021, 4:47 pm | #15 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Re: Restoring a old table grinder
Quote:
[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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18th Jun 2021, 5:37 pm | #16 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,867
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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. David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
18th Jun 2021, 6:29 pm | #17 |
Hexode
Join Date: Oct 2010
Location: Box End, Beds. UK.
Posts: 271
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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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18th Jun 2021, 6:58 pm | #18 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,996
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Re: Restoring a old table grinder
Quote:
You only get one set of hands/eyes. __PLEASE__ play-safe when using industrial power-tools. |
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19th Jun 2021, 5:08 pm | #19 |
Heptode
Join Date: Jul 2010
Location: Wellington, New Zealand.
Posts: 653
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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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21st Jun 2021, 12:36 pm | #20 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,270
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Re: Restoring a old table grinder
If you're quoted less than £400 for the rewind, you're doing well.
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Kevin |