View Full Version : Grinding Wheel Hole Too Small

02-09-2008, 11:26 AM
OK, here's a classic HSM question. I have a 10" pedestal grinder with a 7/8" shaft. The other day I was rummaging thru some old stuff at a used machinery dealer near me and I came across two 10” Norton grinding wheels, unused. I gave the guy $5 for one of them without looking at the hole very closely. Turns out the hole in the wheel is ¾”. I didn’t catch that. So my bargain is not a bargain.

Question, should I just chalk this up to stupidity, or do you think I can make that hole in the wheel bigger? What would I use to ‘drill’ thru an abrasive wheel, and what about making the new hole concentric? (I could take it back, but for $5, it may not be worth the trip)

Your Old Dog
02-09-2008, 11:31 AM
You could probably make the hole bigger without much trouble but by the time you bought a seriously macho mask and armor to wear while using it you'd be dollars behind the game. When something like a 10" wheel comes apart you won't want to be the same room with it. If there is the remotest chance a wheel has been compromised you are playing Russian roulette to use it. If I don't know the history of a wheel i don't want it in the shop. If it's new, does it come to sharp edges or does it look like it may have been dropped or abused causing a chip in the edge? I'd suggest you just write it off as a cheap $5 dollar mistake.

(you probably already know to stand at the side of the grinder and let the wheel come up to speed before stepping into the operating position. If you don't, you may be looking at facial reconstruction bills. Those bills plus the cost of the $5.00 and things could get expensive in a hurry.)

BTW, I don't consider myself to be a safety Nazi. With many problems in the shop you can see them coming. That frequently isn't the case with a grinding wheel as you may get no warning of impending doom.

02-09-2008, 11:54 AM
What YOD said. My wife sells grinding wheels and is well versed in the manufacture of same. The center of the wheel has a higher density that the rest to make it stronger and resistant to compression failure from being fastened to the spindle. BTW, she has also seen the facility used to spin test the wheels. It's a big box made of 1/2" thick steel plate with the spin tester machines inside. They spin the wheels up to 50% overspeed. Some do fail. The box looks like the Hulk was trapped inside and almost got out.

02-09-2008, 04:24 PM
Number one. Before you think about taking a grinding wheel home you should ring it assuming it is a vitrified bond. you hang the wheel with your finger in the hole and tap the wheel with a screwdriver or something similar. The wheel should emit a definite ring. if it goes CLUNK then the wheel is junk and will explode when spun up. You can bore out the center with a carbide boring bar, take light cuts and at slow speed or you can open it up with a carbide burr at slow speed like in an electric drill. After mounting (be sure to use blotters) dress the wheel and you off. Peter

02-09-2008, 04:45 PM
Don't follow that advice, please. Opening the hole on a large wheel is asking for disaster. I wasn't joking when I said that the centre of the wheel is pressed to a higher density. Removing that portion means that the clamping forces will be on a portion of the wheel that has the wrong grain orientation to withstand those forces.

BTW, a better method to test a vitrified wheel that always gives an accurate result is to use a tuning fork. Ring the tuning fork and hold the stem against the rim of the wheel while supporting the wheel by the centre hole. If there is any sort of discontinuity the fork will go dead in a second or two. If the wheel is good then it will amplify the ring from the fork.

J Tiers
02-09-2008, 04:51 PM
Ah, you can drill holes all over a grinding wheel, and then pour hot metal into the holes.......

I know it is true, it was printed in HSM..............(or was it MW?) :rolleyes:

02-09-2008, 05:09 PM
Don't get excited we are only removing 1/16" wall from the bore. have done it with no ill effects. Do ring the wheel again before mounting it. Peter

02-09-2008, 05:29 PM
Good excuse to buy another grinder.

02-09-2008, 06:32 PM
Do anything to that wheel and your as good as dead meat, might not be today, but it could be tomorrow, or the next, time sure aint on your side when you start to do crazy things like your thinkin' of doing.
Either chuck it away and call it experience, or go get a grinder of the correct sized shaft for that wheel.
Been in a room where the grinding wheel exploded, a big cylindrical grinder, wheel around 3 feet across and about 6 inches wide, covered by the normal big heavy cast guard. Found one bit way out on the road, it had gone screaming out the front door. The operator was only a young fella and he drove the wheel into the side of the job, a very load bang was followed by bits smacking all over the shop, at least the young fella had the sense to just drop to the floor and avoid any loose shrapnel. Three of us in the shop and none hit by any flying bits, but we all needed to change our nappies.
Son-in-law's father had a bench grinder wheel go orf, he COULD NOT use his wedding tackle for about three months after where the biggest bit hit.
Choice is yours alone to make, think about it long and hard before you do anything.

02-09-2008, 09:26 PM
According to the Norton rep back in the "70's, stand out of the plane of rotation for 60 seconds when starting any grinding wheel you haven't been grinding with immediatly before, new or not. You don't know what may have happened to it while you weren't looking at it. I've wasted a few moments doing this over the years, but I'm no uglier than I've ever been right now and I have had a few wheels blow when I started them.

02-09-2008, 10:01 PM
Ah, you can drill holes all over a grinding wheel, and then pour hot metal into the holes.......

I know it is true, it was printed in HSM..............(or was it MW?) :rolleyes:haha I think that was HSM, there was a good thread about it on here.

02-09-2008, 10:39 PM
Just to bring it to conclusion, I was aware of the issues with grinding wheels breaking apart. I am not going to try it. Thanks for all the inputs.

tony ennis
02-09-2008, 10:57 PM
ebay it and buy a wheel that's the appropriate size.