Thread: Grinding wheel

This is the page from the Carborundum book I have (similar to the Norton book)
Carbwheels.jpg
No date but there is a picture of a woman operating a centreless grinder in there so I would guess probably around WW2.
Michael

Thanks for all the info guys. So, I think all the info says it looks like the wheels might be silicon carbide, and they don't have to be green but usually are? Still no sign of what RC might be, unless ruby carbide but then its not red either

I have to report a big failure on my part today. Its already too hot in the shed so I have given up but this morning I made a nice snug fit plastic spacer and ran up the big wheel. I started it a little bit, and switched it off before it reached speed, sounded ok. Then a bit faster and off again. Then eventiually let it rip. These motors seem to run up fairly slowly then just when you think its going about full speed, it instantaneously doubles in speed which gave me a big fright. The thing was bouncing all over the floor, heavy stand and all. I thought I switched it off and was taking ages to run down but I hadn't switched it off (few secs but it seems like forever) all my slow tests were nothing to full speed of a 2"wheel that has 0.25mm run out. There's no way I would stand anywhere near it even with all my gear on, it just had an ominous presence. So, I'm a big girls blouse. Too late, I checked the run out, had mistakenly assumed a new wheel would be good and I thought it looked all right spinning by hand and on my slow tests. I'm convinced my spacer was perfect. Anyway, I ran it up slowly again and switched it off and used a diamond dresser on it as it coasted to a halt but it was going to take ages switching on and off, and I couldn't find my new diamond dresser, excuse, excuse... So I gave up and can't comment on how well it cuts carbide.

I tried a dremel kit I got from aldi which had silicon carbide, silicon oxide and aluminium oxide grinding wheels. All of them cut equally as badly, I couldn't really tell any difference. So I cut my inserts by hand on the aldi diamond blocks. With a puddle of kerosene on them, they actually cut quite quickly and I reckon I'm happy with the results, razor sharp. took about an hour or more and my fingers are a bit sore from holding it but at least I'm still in one piece.

I think the washers that hold the grinding wheel are shaped so there is only a flange at the outer radius against the wheel, and i'll check if that is beyond the hole of the smaller disk. I was thinking of using an aluminium spacer with a plastic spacer pressed on just so the stone was not against metal. I've never put an a new stone at all, and don't have any 2"ones fitted, but they are a bit scary if unbalanced. might try the smaller stone instead but I think I'll just order an diamond wheel.

I would think using the on off wall power switch would suit if an unknown wheel was used for the first time, at least you wouldn't have to stand near the control switch for the grinder,that said it still needs to be able to get up to speed.

In regards to the wheel being out of balance and vibrating it needs to be run up to speed and if nothing happens then dressed, if it moves the grinder around the floor then the grinder needs to be secured first.

When fitting a new wheel for the 1st time I rotate by hand and adjust the tool rest so that there is plenty of clearance, turn the grinder on, see what happens then if all good adjust the tool rest so that there is clearance to use a star wheel dresser.

It sounds strange that a new wheel was so far out you couldn't even dress it.

One thing with these wheels to consider is that even when dressed properly that doesn't mean they're balanced. So there may be some vibration just with a bad balance, and why the grinder should always be well mounted. Sometimes as the wheel speeds up/slows down it will go through some harmonic regions when it will vibrate like crazy due to the dynamic imbalance, then settle down at a different speed.

I'm not sure how bad 0.25mm out is, does that sound excessive on a new wheel? I checked things over just there and the grinder has come loose on its stand, in fact it was really just being held by one bolt which was loose as well. I never noticed before because although its an 8" grinder, the wheels are old and probably just 6" and not to badly out of balance.

I think the loose grinder is what sounded so loud and it did run for several seconds, so I think I'd be happy to try as Pipeclay said and switch It on remotely with an extension and leave it a few minutes to build confidence. its a second grinder and I don't need it now so it will go back into the queue if things to be done.

It's a shame nobody has caught footage of an actual wheel explosion (at least not that I'm aware of) in real time as I've heard they're rather "spectacular" when they fail, to say the least.

Sorry can't help. I have been close by when a short very hard thick walled tube flipped itself upright while passing thru a centreless grinder. 20 inch x 8 inch wheel. There was indeed a considerable cloud of dust floating about. There was also a lot of dressing to do on the wheels after. It did not damage the wheels except for gouging holes in them. I used to have the case hardened tube that was the cause, but it disappeared. Lucky it was hollow I guess.

Dean

Originally Posted by RayG

The best thing since sliced bread for touching up carbide inserts is a 3000 grit diamond lap disk.

Grit 3000 Diamond coated 6" inch Flat Lap wheel Lapidary grinding polishing disc | eBay

I've purchased direct from THK's website before, but I'd recommend against it at the moment, I get security alerts when I try to access it.

As far as the wheels you've already got, I've got some of those grey carborundum wheels, I think they came with the grinder originally 30 years ago. I never realised they were Silicon Carbide? Wikipedia tells me that pure SiC is colourless, and the black colour is caused by iron impurities, so I guess that the grey silicon carbide wheels are actually black silicon carbide with a binder that makes it look grey. No idea what causes the colour in green silicon carbide.

Hi Ray,

Can the bore of the THK disc be simply bored out to suit larger spindles? I imagine your GMF has a 5/8" spindle?

//metalworkforums.com/f65/t1936...08#post1853208

BT

Originally Posted by Pete F

Keep your hand on the power switch "in case of unusual noises" if it makes you feel better, but I can assure you it won't do one iota of good if a wheel explodes. I've never personally had a grinding wheel explode, but have other smaller things with less energy let go, and all you hear (if you're lucky) is a bang and that's it. There is nothing left on the arbour so it's not like it's shaking about. If anything I think it's not the best advice as it suggests you may somehow be able to intervene and get a warning, and that could lead to some unsafe practices. In my experience with catastrophic failures there's no warning at all and all you hear is the bang and the feel for remaining body parts/check undies!

Actually nothing will alter the course if the wheel explodes, but I am reminded that about 45 years ago, early in my working life when I was a green young Tradesmans Assistant, and was given a small grinding job. Unfortunately I had been given no training in what to look out for before commencing such a job, and the bench grinder in question had the rest well out of adjustment. The result was as you will have guessed by now, the workpiece went between the wheel and the rest with a mighty loud bang. The wheel did not shatter, but a big chunk of it broke out, and suddenly a small one horsepower grinder was making more noise than a whole workshop and mine concentrating mill together, or so it seemed. The initial steps that I took to save myself from injury were long ones, and fast ones too!
My tradesman was far braver than me and quickly moved in to shut the grinder off, and we replaced the wheel. He also explained the necessity to keep the rest correctly adjusted. I learned something that day I am unlikely to forget, and fortunately the wheel did not continue to break up as he moved closer to turn the power off( on the grinder IIRC)
The point I am endeavouring to make that sometimes it is not a catastrophic failure but a partial failure, and having your hand on the switch might not be such a bad idea, and similarly standing to the side, running the new wheel for some time before getting close and personal all good practises. I do agree that PPE such as face shields are not likely to help much if a wheel catastrophically fails and the wearer of such ppe is standing in the way of the flying debris.

Hi Guys,

One thing that I have noticed in this thread, particularly with regard to wheel vibration and balance, is that wheels absorb water. If a wheel has been stored for any length of time in damp conditions or has got wet then this will cause an out of balance condition even if the wheel is physically round and true to the spindle.

As far as hub fillers go, often a supplier will ask what size spindle the wheel has to fit, and the they will give you a plastic hub to suit both the wheel and spindle. I've bought wheels where the carton has contained several plastic hubs to suit from 1/2" spindles to 1.25" bore wheels. Though that is less common nowadays.

A note about flanges: The flange should only make contact with the wheel via the blotter paper usually provided on the sides of the wheel and the point of contact should be on the outside 10 mm or so of the flange diameter, the plastic hub spacer should also support the middle of the flange. If you examine the inside of a flange, it will have a wide groove in it about a mm or so deep between the inner and outer edges. This is done in order to prevent the flange crushing the bore of the wheel and to ensure that the wheel is gripped over a large area.

Originally Posted by Ropetangler

The point I am endeavouring to make that sometimes it is not a catastrophic failure but a partial failure, and having your hand on the switch might not be such a bad idea, and similarly standing to the side, running the new wheel for some time before getting close and personal all good practises. I do agree that PPE such as face shields are not likely to help much if a wheel catastrophically fails and the wearer of such ppe is standing in the way of the flying debris.

Ha ha, I did laugh about your "initial steps" to solve the problem! I think we've all been there at some point in our journey through this minefield; when it's all going terribly terribly wrong ... run away!!!!

Yes, but my point is that accidents don't generally happen when you expect them to happen, and your excellent story was testament to that. I'm sure you're not advocating using a grinder with your hand on the power switch, yet your accident happened when just generally using the wheel not when it was first mounted. In my opinion anyway, sure when the wheel is first mounted you may want to keep your finger close to the power switch in case it's terribly out of balance, but once it's up to speed if you think you'll be able to prevent anything catastrophic happening by killing the power I think you're kidding yourself, and it may ironically lead to unsafe practices ie "I'll just .... it will be ok I'll kill the power if it doesn't work". There is rarely a chance for intervention once the accident actually begins to happen in my experience, and in less than a heartbeat it's over. All the interventions need to happen before the accident to prevent that chain of events from occurring.

Many people on the board now have surface grinders. The one thing I've taken away from using mine is that there are those who have thrown a part, and those who will throw a part. It shouldn't happen. It happens. Invariably it will be caused by doing something stupid, but the thing is how fast it happens. One second you're looking at your part, the next second you're looking at an empty chuck and there's some unpleasant noises going on around you as a part ricochets around the room at high speed! No amount of hands on power switches is going to prevent accidents like that I'm afraid.

As an aside, I've read reports of wheels exploding and even with guards the lower body injuries can be quite severe. Without the guards the shrapnel can definitely kill.

Originally Posted by Anorak Bob

Hi Ray,

Can the bore of the THK disc be simply bored out to suit larger spindles? I imagine your GMF has a 5/8" spindle?

//metalworkforums.com/f65/t1936...08#post1853208

BT

Hi BT, Yes, I just ran a tapered reamer through till I got a neat fit, since you are working on the flat side of the disc, it's not that critical for it to run true. I think I saw a picture where BobL had one mounted on the side of a CBN wheel?

Ray

PS. Sossity, for a new wheel to be so far off balance that it bounces the grinder across the floor, there must be something else going on, 0.25mm runout is not going to cause that. Even only having one bolt holding the grinder down is unlikely to cause that severe reaction. If you take the wheel off and run a DTI on the grinder shaft, what does the run-out look like? Also is there any play in the bearings? If the bearings are completely shot it might rattle around like that?

Originally Posted by Pete F

One second you're looking at your part, the next second you're looking at an empty chuck and there's some unpleasant noises going on around you as a part ricochets around the room at high speed!

I think you mean, one second you're looking *at* your part, the next you're looking *for* your part.....

BTDTGTTS.....

PDW

Originally Posted by RayG

Hi BT, Yes, I just ran a tapered reamer through till I got a neat fit, since you are working on the flat side of the disc, it's not that critical for it to run true. I think I saw a picture where BobL had one mounted on the side of a CBN wheel?

Ray

Bob, I have bushed then bored at diamond wheel as I found the OD was quite round so this was the bore was concentric. Just popped it in the lathe.

I have ground a lot of carbide over the last 12 months or so, mostly on the surface grinder. Parts up to 150x50. With SiC one thing i noticed was the wheel wear is approximately the same as the material removal. Ie your downfeed is .02mm and .01 comes off the wheel and .01 comes off the job. This is of course dependent on job size and wheel hardness, but seems to hold true on bench grinders as well. Push hard and your wheel just disappears in front of your eyes.
Having been screwed around by pretty much every major abrasive company in Aus i bought a couple of diamond wheels out of China, these have exceeded my expectations by miles and cut so much cooler and more freely than the SiC wheels. The biggest issue is dressing them!

Originally Posted by Ueee

I have ground a lot of carbide over the last 12 months or so, mostly on the surface grinder. Parts up to 150x50. With SiC one thing i noticed was the wheel wear is approximately the same as the material removal. Ie your downfeed is .02mm and .01 comes off the wheel and .01 comes off the job. This is of course dependent on job size and wheel hardness, but seems to hold true on bench grinders as well. Push hard and your wheel just disappears in front of your eyes.
Having been screwed around by pretty much every major abrasive company in Aus i bought a couple of diamond wheels out of China, these have exceeded my expectations by miles and cut so much cooler and more freely than the SiC wheels. The biggest issue is dressing them!

I've been playing about with a Norton brake dresser. I think they would be easy enough to make, just a freewheeling small Alox wheel with an adjustable brake, sort of a rolling action, spin it up by hand just before contacting the wheel, so that it rolls and abrades at the same time. Sort of difficult to describe, but easy enough to do. This is on resin type diamond wheels.

There's a Norton video DVD on how to use a brake dresser, I believe they were supplied with the unit, but I've never been able to source a copy of the DVD.

Ray