After having received such useful advice on my first question to the knots forum, I have another problem for which I would like to profit from your collective wisdom. I am worried about my 6″ bench grinder. It is a cheap model from a Canadian box store. I have had it for about 4 years. It didn’t run very round from the beginning. But lately it is having seizures that get even the table to rattle in sympathy.
I don’t know if it is the bearings, whether the disks are not round or not properly seated. Is there an established way for testing and adjusting a bench grinder. Or do I have to chuck the culprit? I am concerned that sooner or later something will give.
Replies
1. Run it without anything mounted on the arbor. If it still vibrates then the problem is with the bearings, or conceivably the shaft has been bent. If you turn it by hand can you sense any freeplay, or any difficult point in the turn?
2. If the shaft runs smoothly without anything mounted, then you've isolated the problem to the stone itself. Try mounting a new one. There are tools which can true a worn stone, but if you're not adept I'd recommend just replacing the stone.
David Ring
http://www.touchwood.co.il/?id=1&lang=e
It's likely that if the arbor was off a tiny bit, you wouldn't see it without a stone. So i don't know if that test will work. It's worth a try, but it you don't perceive wobble or play doesn't mean it's not there.
Stones can easily do this. You could try truing up the stones a bit. Or they could have become loose.
I'm having troubles with my grinder. It's cheese. Life is too short for problem grinders. Who likes working with or on things like this? I didnt' get into woodworking to be a machinst. I say chuck it and get a grinder you can trust. Grinders are tools few of us want to spend money on, but they are clearly a tool you can throw money at aand these sorts of problems go away. Get a good Baldor grinder and at least one SG wheel.
(my SG wheel needed alot of truing- I think I had to compensate for bad cup washers - Woodcraft 8" slow speed)
Adam
I like working on my grinders. I just like being in my shop ! But I was called crazy earlier today here. Thing about being thought crazy; people give you allot more leeway for behavior. (Leo Buscaglia said that. People called him crazy but he had a PH.D. so we should listen to what he has to say. Right?)
Any way. Grinders. Worth taking the wheel off. While you got it off put a dowel or screw driver or some such through the hole then tap the wheel with a screw driver handle. It should ring like a dinner plate. If it goes thunk instead of ring it may be cracked so don't use it. (probably not cracked or it would have flew apart and killed every body in the room by now)
Ok to check the shaft for bent or not bent take a hunk of coat hanger wire or something that you can clamp near the shaft. Make it just touch the side of the shaft near the end of the shaft. Now turn the shaft by hand by the other end of the grinder.
Does the shaft move toward the thing you clamped near it then move away from it leaving a gap then move back at regular intervals? If it does then shaft may be bent. If it just stays about the same as you turn the shaft it is pretty straight.
I said regular intervals because if it moves in and out but in random intervals your bearing may be very worn and the ball bearings (assuming it has ball bearings) are no longer round and the places they role on are no longer smooth and so the lumpy worn things are just bumping around and pushing the shaft here and there.
As ring says at this stage you will sense slop in the bearing. Grab it very firmly and yank it back and forth perpendicular to the length of the shaft. Most cheep grinders if you were to grab the shaft and push it in and out along the length of the shaft it would slop a bit and this is usually not a problem if it is just a bit.
About all wheels need to be trued so getting a new one may not fix the vibration problem. Truing the wheel to make it rounder, called dressing it, is not difficult. Wear a mask for the abrasive dust that will come off.
You can get a dresser for not too much. Some have wheels and tungsten star wheels. Some have a chunk of abrasive harder than the stone and some use chunks of diamond. they are flawed industrial diamonds so really not expensive. It does not matter much which type you get.
The thing we did earlier with the object clamped near the shaft is basically what you do with the dresser but you let it touch the wheel (don't clamp it) while it spins under power. As the dresser wears away the high spot you keep moving it in a tinny amount at a time until it touches the wheel all the way around with out pushing the dresser back toward you and you are done. No big deal.
The dresser is handy if you get metal smeared into the pores of the stone you can clean it out by taking off that layer of the stone in the same manner we did to dress the bump out.
Also some cheep wheels are too hard and get to where they do not grind but just kind of rub on what you are trying to grind. If you take a pass with the dresser it will freshen the wheel by taking all this smooth stuff off and make the abrasive surface nice and scratchy again so it grinds better.
Heck if dressing the wheel does not take care of the vibration and you end up getting a new grinder you will still want the wheel dresser for the new grinder.
PS: one other thing that just occurred to me. Make sure the hole in the stone fits the shaft snugly. If there is a bigger hole in the stone than the shaft requires to just fit then go to a hardware store and get some grinding stone shims to improve this fit. They are just short lengths of plastic tubing in different wall thicknesses.
Edited 10/22/2008 11:14 pm by roc
"It is a cheap model from a Canadian box store"- no useful comment to make there.
"It didn't run very round from the beginning".- You seem to be saying that the wheel(s) were out of round from the start. If you did not dress them to be true from new they would only get worse with use and wear.
You can expect to dress any new wheel -they very rarely run true: they will have radial run out or axiel run out or both, and that applies to expensive seeded grit wheels from Norton and the rest of the big boys.
Check that the nuts are tight and the paper washers are intact-these are important for the well being of any wheel and should not be discarded. Do not over-tighten and be sure that you actually are tightening-many bench grinders have a left hand thread on one side and a right hand on the other....
Check that the wheel flanges are true- clamp them together minus the wheel and spin the shaft-they should have no visible run out at the inner sides.
Be sure that the wheel bushes are a close fit- too loose and the wheel can run out of true which will cause the vibrations you talk of. These bushes are typically plastic and often are too loose a fit-you can compensate for this with masking tape or tin foil-but not really a good plan.
Bearings- run it without wheels- it should run smoothly and quietly. I would expect no undue play as in worn bearings on a newish item like this-but it is remotely possible that the bearings suffered corrosion from incorrect storage and lack of use-if so they will make noise and if you spin the shaft by hand you will feel roughness. Hopefully it actually has ball bearings...
Absolutely no bench grinder will work as intended if the wheels are not true-that is why a wheel dresser is an essential accessory.
However, cheap nasties from a box store will in addition have some, all or more of the faults I have mentioned here- so it pays to get something reputable right from the start, unless you are machine savvy and prepared to re-build it.
I hate "cheap" bench grinders-they are in fact very expensive (;)
Philip Marcou
Edited 10/23/2008 5:55 am by philip
When was the last time you 'dressed the stone?' Machines do not like spinning Oblongs!
Thanks to everyone. Yes, you were all right. grinders like to be dressed. It works fine now.
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