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Alistair Hosie
06-11-2005, 01:18 PM
I have a very good quality eight inch heavy duty bench grinder it has a problem that since I bought it second hand it wants to vibrate off the stand. I have bolted it down it is useable but the vibration is unnaceptable .I only have one wheel on it could this be the problem?I bought a diamond truing stick should I refit new wheel which I have ?or try truing up (the present wheel) with the wheel in situ? or fit a new pair of eight inch wheels?I don't have any other way /device for truing up the wheel of the machine ,advice please.Alistair

jim davies
06-11-2005, 01:32 PM
How smooth is it when run with nothing on the shafts?

Smtty58
06-11-2005, 01:34 PM
I would pull the wheel off and see if the grinder alone vibrates. Then when remounting the wheel make sure it is centered on the adapter hub. Don't dress it in the conventional bench grinder way, you'll just follow the out-of-roundness. If you have a diamond, use that. If not, use whatever is at hand. Clamp something to the dresser that will follow the lip of the toolrest, and run back and forth just knocking the high spots off the wheel. Keep readjusting the clamp untill you can skim the wheel as round as possible. Don't expect perfection, I've never seen a bench grinder that didn't vibrate.

Jpfalt
06-11-2005, 02:25 PM
First comment, get a diamond dresser. There is no substitute for forming the wheel.

Dress it true with the diamond. If it's not balanced when dressed true, then most likely the problem is the wheel. Most are pretty good, but occasionally some come out that are way out of balance. You can either replace the wheel with a good one or put on a balancing collar. Using a balancing collar can even adequately compensate for an untrue grinder arbor. The simplest form for a balancing collar is a disc of about 1/4 or 5/16 plate with a ring of tapped holes near the outside diameter. You can either put set screws into the holes and moving them around until things run smooth. Then a drop of lacquer or superglue will keep the setscrew from backing out. It's important not to drive the point of the set screw into the side of the grinding wheel. In extreme cases, I have put in lead slugs instead of set screws. Usually you have to counterbore the center hole in the collar to accomodate the length of the grinder arbor. Also, the wheel side of the collar should match the shape of the collar on the other side of the grinding wheel as collars of different contact diameters put extra unwanted forces into the wheel that could cause the wheel to break. The key is that once the collar is bolted on, don't move it until it's time for the grinding wheel to come off. As the wheel wears, the balance may change due to heavy and light spots being dressed away and moving the set screws may be required.

With dressing, true with the diamond and then lightly take a pass with the star wheel dresser to get a free cut. I usually turn the grinder off after truing and then while it coasts down run the pass with the star wheel. It reduces the wear on the star wheel and keeps you from over dressing wiith the star wheel. When properly used, you don't get sparks when using the star wheel.

One of the lowest tech ways to figure out the heavy side is to put a dial indicator against the grinder frame near the wheel and put a strobe light on it so you can stop the indicator wobble. You mark the collar on the grinder and note when the grinder frame is pushed farthest forward which is also the point that the lightest spot on the wheel is also forward. When you identify the spot add set screws to the collar. Otherwise, take two screws next to each other in the collar and move them around until things get smoother. Then add two more and do the same. It's tedious, but it works after a while.

Alistair Hosie
06-11-2005, 03:29 PM
Sounds good guys will try these tips tomorrow . Alistair

precisionworks
06-11-2005, 03:47 PM
http://www.jsyangshi.com/cp/l-d1.jpg


This is the easiest type of dresser I've ever used. Costs $10-$15, used by gently feeding the diamond face across the wheel.

I noticed that the wheels on my new 7" Baldor kept coming to rest at exactly the same spot, indicating that counterweight needed to be added. By using superglue & various size hex nuts, I found the weight needed. Then that was TIG welded onto the nut that holds the wheel. Vibration gone.

------------------
Barry Milton

Mcgyver
06-11-2005, 07:48 PM
check out

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

As JP suggested, it gets to the root of problem but seems to have good methodology vs trial and error (then again i haven't done it yet, but plan to soon http://bbs.homeshopmachinist.net//smile.gif

lost in la
06-12-2005, 12:55 AM
If the wheel is still out of balance after truing up the od, trim up the sides with a diamond. This might take a bit of doing but a lot of grinding wheels are not true to their bore. Also, the bore may be too large for the shaft that you mount it on. If it is loose by only a little I use a bit of scotch tape inside the wheel bore to make a snug fit then redress.
If this does not do the job the wheel may be out of balance due to uneven processing at the factory which only balance weights will solve.
Lost

Evan
06-12-2005, 02:18 AM
"I've never seen a bench grinder that didn't vibrate. "

Whaat?? It should be smooth as silk. If it isn't then something isn't right. A quality wheel will be well balanced from the factory. If it isn't then get your money back. Don't try to mess with it, something is wrong.

As for wheel dressing use a diamond. I have a couple of half carat diamond dressers and it is amazing how they will take the wheel true in a few seconds. Any wheel. Keep your grinders away from the other tools.

Norman Atkinson
06-12-2005, 05:20 AM
Alistair,
I do not wish to detract from anything written so far.

Nevertheless, when a wheel- or both wheels are out of balance, you should be asking questions of whether the present wheels are
suspect or whether the rest of the grinder is suspect. The latter point has already been raised. Is the grinder smooth running- without wheels? It is only when you can say "yes" to that that you can move on to what is stage 2.
You then put the retaining washers and nuts on- and check.

Then you have stage 3 and that is to go out and buy 2 decent wheels from say Cromwell which has a place in Glasgow or another good firm.

I recall the words of the late Tom Walshaw writing as Tubal Cain about abrasive wheels.
The safety rating of unknown wheels is NIL.

Reams of advice have been laid down as the Law and Practice on this subject. Respectfully, good friend, might I suggest that the "Bucket Man" gets the present wheels.

Norman

J Tiers
06-12-2005, 10:04 AM
I assume the wheel is not new. In that case, the best idea may be to dispose of the wheel, and replace it.

It is probably one of the gray wheels anyway, which are always the wrong grade wheel, normally too hard.

I found also that new wheels have a plastic liner in them, instead of the old lead. makes getting the bore true difficult.

If the bore is not true, then truing the wheel may help a bit, but it will still vibrate. I suppose weighting is all you can do then.

Mcgyver
06-12-2005, 12:28 PM
on the subject of the plastic liners, should one ever decide to make one with a "better fit" in an effort to obtain truth in the wheel, be aware that a lot of that clearance is on purpose. It's designed to allow for expansion as the wheel warms up

[This message has been edited by Mcgyver (edited 06-12-2005).]

darryl
06-12-2005, 03:35 PM
'expansion as the wheel warms up'

How much of that can there actually be? How does that relate to the motor shaft expanding also with heat from the bearings and the motor itself? I'm inclined to believe that any plastic bushing that is a snug fit, or finger pressure fit into the wheel and over the shaft is going to be ok. I've seen them being too loose where there's play, like maybe 10 thou or more- is this what you're referring to as being 'on purpose'? I guess I erred when I machined my own bushing to be a better fit, such that the wheel wouldn't go off balance by having that 'play' in there. Seems to me also that if you mount a wheel with a loose bushing, then true it, it could still be off balance because it was never centered properly to begin with. And it could go out of balance if it shifted on the shaft, requiring re balancing and truing again. And again, and again- doesn't seem right to me.

More input on this subject would be good, thanks.

Mcgyver
06-12-2005, 04:30 PM
What, you mean you’re not familiar with Subchapter 7. General Industry Safety Orders,
Group 3. General Plant Equipment and Special Operations, Article 21. Use, Care, and Protection of Abrasive Wheels, §3580. Mounting. (b)??

Arbor size. Grinding wheels shall fit freely on the spindle and remain free under all grinding conditions. A controlled clearance between the wheel hole and the machine spindle (or wheel sleeves or adaptors) is essential to avoid excessive pressure from mounting and spindle expansion. To accomplish this, the machine spindle shall be made to nominal (standard) size plus zero minus .002 inch, and the wheel hole shall be made suitably oversize to assure safety clearance under the conditions of operating heat and pressure.

I originally read about this in a Norton flyer and googled the about so you guys didn’t think I was imaging things. I don’t know the manufactures interpretation of “suitably oversized” It seems plausible that with a very low clearance, that across 8" of wheel under heavy and continuous use there'd be thermal expansion enough to add to the forces making the darn thing want to come apart.

Given Norton presented the idea and there's a standard on it, there’s something there….maybe a home shop guy is never going to heat a grinding up to that level, however with a bunch of grinders; I have a deep rooted fear of a wheel giving it up and have no interest in trying prove this wrong http://bbs.homeshopmachinist.net//smile.gif


[This message has been edited by Mcgyver (edited 06-12-2005).]

Mcgyver
06-12-2005, 04:32 PM
found the Norton reference....
http://www.grindwellnorton.co.in/GrindingTech/pdfs/BalancingOfGrindingWheels.pdf

i'd forgetten expansion is also from the shaft - bearings etc.



[This message has been edited by Mcgyver (edited 06-12-2005).]

Alistair Hosie
06-12-2005, 05:06 PM
Good information there,thanks.
Well I took of the guilty wheel etc and the machine is perfectly sweet when run with hothing but the bear shafts so will put the wheel back and try truing it with a diamond dresser.Alistair

darryl
06-12-2005, 11:51 PM
Thanks for the extra input, Mcgyver. I had to question what you first said because the play I have seen in those plastic bushings is in the ten thou or more range, and that is out of spec when compared to the two thou or so suggested in the articles. That's more like what I thought it should be, so there, I'm alright again. I'll stick with my practice of making my own bushing if the one supplied is sloppy, but I'll make sure to have some small clearance.

Now I suppose if anyone wants to get technical, they would have to do a static balance test on any new wheel if it didn't come already marked with that info. The mounting of the light side up procedure before truing sounds logical, and even for a small grinder and wheels would be a good practice.

madman
06-13-2005, 09:54 AM
Must suck to only have an eight incher.Up here in northern canada most have 9 and a half inches.

Evan
06-13-2005, 11:20 AM
First, when you buy a grinder that has wheels included immediately remove them, break them and toss. Then go buy some real grinding wheels. Ask the supplier if all their wheels are 100% spin tested. If they cannot instantly answer that question in the affirmative then go elsewhere.

Mcgyver
06-13-2005, 01:10 PM
Evan, Can you give some more insight re the comment on suppliers that spin test? I've only ever bought wheels from KBC or local industrial supply houses. On a good day, the guy at the counter is vaguely aware that what he's selling is a grinding wheel.

is the spin test something the supplier does? do you have to find a specialty abrasives vendor for that?

Evan
06-13-2005, 03:17 PM
The wheels are spin tested when they are manufactured. At least the good ones are. And yes, you need to find a specialty abrasives vendor. I see you are in Canada so I will recommend you speak to my wife. She sells abrasives and grinding wheels of every type and style. They are all 100% spin tested. According to my wife all major name brands manufactured in North America are spin tested. As for Asian made wheels, nobody knows. I wouldn't trust them at all.

My wife is the expert on this so if you have any questions send me an e-mail at the address in my profile and I will forward it to her.

Alistair Hosie
06-13-2005, 03:42 PM
I put the old wheel back on and it vibrated so I trimmed it up slowly with the diamond dresser and its quite good (not perfect) but bearable enough for me to use without wingeing .Alistair