Thread: Benchtop Grinder

Thanks for the heads up. I'm sort of looking around for another 200mm grinder myself and I saw the one you have advertised somewhere recently. Also read a thread on one of the USA forums where someone had bought a 200 mm grinder but when they opened it up it turned out it had a large case with a real small diameter stator and rotor in it. No wonder it didn't have much power.
I have a real old GMF that I have had for 30 years and it was probably that old when I got it. Put a set of bearings in it about 25 years ago. The start windings have died so I have to give the wheel a small spin when starting but apart from that it is still running great. I'd like to get another one.

regards
bollie7

Originally Posted by bollie7

The start windings have died so I have to give the wheel a small spin when starting but apart from that it is still running great. I'd like to get another one.

Could be just a dead starting capacitor?

Originally Posted by bollie7

Thanks for the heads up. I'm sort of looking around for another 200mm grinder myself and I saw the one you have advertised somewhere recently.

I had seen an ad around for this grinder too and remembered it is from H&F sale catalogue, I recently bought a 200mm bench grinder from Carbatec so I dont need another but I did see this one and was wondering what it was like with its German name an all, guess we all now know its not any good !!

Matt.

Originally Posted by Big Shed

Could be just a dead starting capacitor?

I don't think it has one.There isn't one on the outside. Mind you, its been 25 years since I had it apart so who knows whats inside.LOL. Its one of those jobs in the "I'll get around to it one day or maybe sooner if it stops entirely" bin.

bollie7

Originally Posted by bollie7

I have a real old GMF that I have had for 30 years and it was probably that old when I got it. Put a set of bearings in it about 25 years ago. The start windings have died so I have to give the wheel a small spin when starting but apart from that it is still running great. I'd like to get another one.

regards
bollie7

Hi Bollie
Theres the rub
The "old" GMF bench grinders are nothing like the "new " GMF grinder.

The couple we had in the Man Arts department ran on for a good time once turned off . They had really top quality bearings and the balance was great.Have a look at a new one running and switch it off.It will stop very quickly..

Also check out the wattage of the old against the new.

They just don't make them like that any more. ....sigh!!!!

I suppose the best one could do would be to static balance the wheel flanges .


Grahame

Grahame
I know what you are saying. Mine's that old, it has a brass ID plate and the wheel guards are cast iron. The end covers were missing when I got it but I salvaged a couple of end plates of a later model from a place I worked at once. We had a grinder set up with a linisher on one end and a wire wheel on the other. Came in one morning to find someone b*****d had busted into the compound over night and pinched it, along with a bit of other gear. So we ended up with a set of end covers but no grinder. I grabbed them out of the dump skip.
I have nice little Sher or Skil grinder that belonged to my Dad. I just shoved in in a cupboard when we were cleaning his stuff out after he died, without really looking at it. I thought it was a 150mm one but when I dug it out a couple of weeks ago I discovered that it is actually a 125mm (5") one. Runs nice but I haven't found any replacement wheels for it yet. Its really a bit small for what I want anyway. It might end up becoming a motor to drive something else.

regards
bollie7

Originally Posted by Grahame Collins

The couple we had in the Man Arts department ran on for a good time once turned off . They had really top quality bearings and the balance was great.Have a look at a new one running and switch it off.It will stop very quickly..

I got a carbatec bench grinder that can take a while to slow down, at least 30 seconds maybe more like a minute but I havnt really timed it. Was only $100 on special for 8" one and it came with a couple of nice wheels. It does shake a little but I think its more out of balance wheels that anything, and that can be fix with a special tool I cant remember the name of at this time.

Matt.

If the grinder was (SHACKING) from new and the wheels were allready fitted I would be checking to see if the wheels are bushed and if so maybe replacing the bushes,the only time the wheels would be out of balance is through use ,if not through use there may be a problem.
The only way to get the wheel back in balance is to dress them with a Grinding Wheel dresser either star wheel,stone or diamond.

Originally Posted by Grahame Collins

The couple we had in the Man Arts department ran on for a good time once turned off . They had really top quality bearings and the balance was great.Have a look at a new one running and switch it off.It will stop very quickly..
Grahame

That reminds me Grahame of my neighbour who comes up to talk to me every now and then, and is forever trying to turn off my bench grinder. I don't know what brand it is, but its an oldie, and runs for about five minutes after you turn it off. My neighbour often goes over while I'm not looking and flicks the switch to "turn this off for you". This gets the damn thing going again and so on.... This means that if I'm using the grinder when he turns up, it runs the whole time he's there! I've explained to him a few times now that it runs for five minutes after you turn it off, but he's struggling to accept it.

Bollie

your GMF motor may just have an open centrifugal swtch, or dirty switch contact, or a crook connection to the start winding inside.
Get your electrician to have a quick look inside.
An easy fix sometimes.
These type of induction motor normally dont have a start capacitor, as there is little requirement for starting torque.
They just use a "resistance start" winding, connected by internal centrifugal switch, so as to have two windings connected in parallel at start, and then run on one winding.
The start winding uses the thinner diameter wire, so as to have some resistance (and phase lag), and the run winding uses thicker wire to have lower winding temperature rise by "copper losses".

cheerio, Mike

Hi,
For those it may be a help to
here is info for balancing the bench top grinder wheel.

http://assortedtips.blogspot.com/200...imbalance.html

More on concentricity and balance.
http://www.grindwell.com/GrindingTec...dingWheels.pdf

There was also another one just on balancing the bench grinder wheel flanges.

It dealt with adding balance weight in the form of lead into holes drilled in the wheel flanges, much like the wheel weights on a car. It is relatively simple to do.

What follows is similar to what I refer to above.
http://www.newwoodworker.com/reviews/onwybalrvu.

I will post the other if I can find it.

Cheers
Grahame

Hi


Heres the other site on as mentioned above
re balancing bench grinder wheels.

http://homemetalshopclub.org/news/sep04/sep04.html

Grahame

Originally Posted by mike48

Bollie

your GMF motor may just have an open centrifugal swtch, or dirty switch contact, or a crook connection to the start winding inside.
Get your electrician to have a quick look inside.
An easy fix sometimes.
These type of induction motor normally dont have a start capacitor, as there is little requirement for starting torque.
They just use a "resistance start" winding, connected by internal centrifugal switch, so as to have two windings connected in parallel at start, and then run on one winding.
The start winding uses the thinner diameter wire, so as to have some resistance (and phase lag), and the run winding uses thicker wire to have lower winding temperature rise by "copper losses".

cheerio, Mike

Mike,
All the GMF grinders I have seen are Capacitor-run motors, ie no centrifugal start switch. They start and run with the capacitor always in circuit in series with the start winding to provide a pseudo two phase motor. It is not uncommon for this capacitor to fail after many years. On early (pre 1980s) machines the capacitor contained PCB and must be disposed of responsibly.

Thanks to all for the advise offered. I've put the wheel washers on a lapping plate and they are way off, this is confirmed by rotating the washers with the wheel mounted, the lateral displacement of the wheel varies from about 1.5 to nearly 3mm depending on the phase of the washer. I suppose one can't expect too much from a piece of stamped steel, anyway the plan is to either true the existing ones up or make new ones, plus get a decent collar on the spindle shaft for them to bear on. Just hope I won't be the next one to replace the bearings. When I purchased this unit I was tempted by the 10 inch model but at nearly 3 times the price found it hard to reconcile for home shop use.