OK, drills and circular saws and sanders seem to work great right out of the box - why is it so hard to get a grinder to run smoothly?
I’ve had 3 of them now, and fussed extensively, and still they vibrate like hell and often only use part of the wheel circumference because they run out of true and out of balance.
The wheels themselves often have soft paper disks on the sides of the wheel around the hub, and manuals say you’re supposed to clamp the wheel in the right spot so the impression in the paper locks the wheel in place. True enough, there’s a few mills of clearance over the shaft, and often what looks like a malleable lead bushing on the ID of the wheel. But how do you establish the original position accurately? I’ve tried replacing wheels and holding the grinder with its shaft vertical so I can play with the wheel and turn it by hand and inspect it before tightening the mounting nut.
I’ve bought wheel dressers, the kind with the star-shaped wheels and the kind with a diamond point, and they do remove wheel material but don’t get rid of the vibration. Looks to me like the shaft curves a bit under the stress of unbalance, so of course the dresser makes the OD run true in this condition, but the thing still vibrates incredibly. Mounting the entire unit to a heavy support passes the vibration along elsewhere, but I wish it weren’t vibrating to begin with.
In machine shops I see sometimes very big grinders, with maybe 24" wheels, for example mounted on lathes to grind the ODs of web rollers or calender rolls to 0.1 mil or so. Those don’t look like they’re vibrating, and the bolts holding the lathe together don’t vibrate out every 20 minutes.
I have no clue as to the reason for your problem except maybe the wheels were made in China. I’v never had a problem like that but I haven’t bought a wheel in years.
I will say that I would be careful about running unbalanced wheels. Or at least about standing in line with the wheel. Such wheels can disintigrate catastrophically.
Perhaps your grinder is of poor quality or your shaft is warped. Are you using a wheel that is rated for the rpm rating of your grinder? If you continue to use it, make sure you do the following (for bench grinders): insure the eye guard and wheel guards are in place. Make sure the tongue plate is no more than 1/4" away from the wheel. Never grind on the side of the wheel. Always perform a ‘ring test’. Other precautions here (PDF), including how to perform a ring test. As mentioned, when a wheel comes apart, severe injuries are usually the result. The wheel throws shrapnel like a grenade, usually causing abdominal injuries.
Third this. In all my years of using grinding wheels, I’ve never ran into this problem, even when the wheel was damaged and had hunks missing out of them.
Among woodturners (and others interested in precise tool sharpening) out-of-balance grinding wheels are a recognized problem. High-quality wheels are available, and these tend to have better balance. Also available are wheel-balancing jigs which (with some care) seem to work quite well.
Well, this is a mystery. I don’t know what I’m doing wrong.
I have had 3 different grinders bought in about 1965, 1982 and 1995. I have bought perhaps 8 wheels over the years for them. They’ve been above-average consumer brands and models. Multiple times I’ve thought, surely I can fix this, let me get a good quality new wheel and spend a little time on trying to get it right, and still they vibrate much harder than I think they should, and walk off the workbench unless they’re bolted down. Last time I took the guards off so I could see all the way around, and held the grinder with its shaft vertical, and fiddled with tiny strips of thin shim to try to get the shaft centered in the hole before clamping. Still very noisy. (Don’t worry, I have guards on it again).
How much is it supposed to vibrate? Is it supposed to be much noisier than the motor running without a wheel?
I’m a machinist and have spent a lot of time in front of a lot of grinders.
I assume you are talking about a 6" bench grinder. How much vibration are you talking about? Scooting around the table or bouncing up and down? “Walking” is normal vibration. You are spinning two hunks stone around at a pretty high RPM. It’s not like a drill or saw blade, mass wise.
Every grinder I have either in my basement or the two at the shop I own are bolted down. Otherwise they would be all over the place. As you said, truing up the wheel with a dresser helps a little. If one part of the wheel has a high spot you can see that it will spin off center and add to the vibration.
Surface grinders and other big grinders often have a tapered shaft, eliminates any play. Also they have much better bearings.
Mr. Goob, this is what I’m talking about. My grinders walk around. They don’t scoot or bounce. So, walking IS normal vibration.
And I didn’t think it had to be. Spinning a wheel that’s somewhat heavier than a sawblade doesn’t mean it has to walk (and one of my grinders was a 4", whose wheels are probably lighter than my 10" sawblade). After all, the rotor inside the motor is heavier still.
What does the tapered shaft do? That is, where exactly is the taper used? In the connection between the shaft and the wheel hub? Does the wheel hub have a female taper? The stone itself wouldn’t slide over a taper, it’d split, I know. Are big grinding wheels balanced when you buy them? I can’t imagine smaller wheels are.
They call these toolroom wheels, right?
Maybe I should ignore the whole thing, but it doesn’t seem right…
A toolroom wheel could mean anything. It could be the composition of the wheel, the shape, grit, or any number of things. Marketing BS.
As to tapered shafts, I’ve only seen them on surface grinders or other industrial tools. Not something to find in a home workshop. The shaft and the wheel have a matching taper. If you were to look at the wheel flat on one side, then flip it over you would see the hole is a different size. It’s pretty slight, but enough to make for a snug wobble free fit.
What I’ve done in my shop with seldom used bench tools is to use wing nuts on bolts. Pretty quick but sometimes a pain. One of the grinders at my shop is on a board hinged under the end of a bench. With some hardware from a drop leaf table I can swing it up and lock it into place when I need it. Then fold it under out of the way the rest of the time.
The taper provides a very strong friction fit between the driving shaft and the tool. No screws or bolts are involved. You wouldn’t think smooth bare metal to smooth bare metal would work, but a taper can transmit a lot of torque without slipping. Nearly all drill presses mount the chuck on a taper.
As for the stones, they’d have a hub with the appropriate female taper.
Taper-mount “centerless” wheels are quite expensive - I’m hoping that part of their several hundred dollar cost (per wheel!) includes being balanced and true right out of the box.
>Taper-mount “centerless” wheels are quite expensive - I’m hoping that part of their several hundred dollar cost (per wheel!) includes being balanced and true right out of the box.
Hmm. This is the sort of proper fix I suspected was out there, but not at hundreds $.
The only expensive taper mounted wheels I’ve bought ( or my company did ) are around $ 150+ diamond cup wheels for special grinding of carbide tools. Their money not mine.
Not to be cavalier about the company cash, but spending $50,000 a month on perishabile tooling mkes one a bit jaded.
>Not to be cavalier about the company cash, but spending $50,000 a month on perishabile tooling mkes one a bit jaded.
Quite. The river that flows around me runs at about $1,000,000 an hour, and I have ALL KINDS of reasons to want to make it run better, even if just a little bit.