Thread: Grinding wheel "bounce"

Get a wheel dresser and dress it true.

Hi Dan...

Nah... I dress it whenever I use it and it still goes off. Sorry I should have mentioned that in the original post. I think its something altogether more sinister!

Originally Posted by philly

I dress it whenever I use it and it still goes off. Sorry I should have mentioned that in the original post. I think its something altogether more sinister!

You can get a bounce effect if the material you are grinding is too thin ie 2mm plate on a coarse wheel and the edge digs into the wheel
This can also happen if the angle of the material to the wheel is incorrect the material is pressed too hard onto the wheel and the tool digs in to the wheel
or if the material vibrates and flexes then digs in.

As you are sharpening lathe tools that don't flex and I take it these are wood working tools ,then perhaps your angle of approach to the grinding wheel is too sharp and you may find there are better methods of sharpening the tools.

The trouble with life is there's no background music.

Quote : the tool tends to bounce off the wheel rather than sit on it

Phil,
Are you using a tool rest on the grinder?

Phil I would have a look at the wheel you are using. Wheels are graded by the grit (coarseness) speed they run at the hardness of the abrasive and the hardness of the bonding agent. Because you said you are on your fourth wheel I am guessing that you have a coarse silicon carbide wheel that you can get off the shelf from any hardware store. These wheels are best for grinding back mild steel that has been cut with a saw. That is cleaning up the dags. If you cut something with an oxy torch they aren't too bad but usually not hard enough. For tool steel as in a Woodwork chisel you need a finer wheel. This could be the reason it bites and "bounces" back at you. The coarse wheel is suddenly grabs at the chisel then chucks it out. I am not sure what hardness they make turning chisels to. Normal woodworking chisels sharpen very nicely on the various handstones. I would recomend these hand stones to finish the blade off once you have done the rough grinding on a grinder. You may not need to use the bench grinder all the time although they are often useful depending how much of you need to grind it down to bring the edge back.

As rodm said using the rest is crucial. You can hold the chisel on the rest and by altering the pressure of your hand squeeze it in against the wheel. It helps too to set the rest to the angle you want the blade to be, so you have a guide to get you to the right place.

There are catalogues from the various abrasive manufacturers with specifics on their grinding wheels. You can find in them easily the wheel that will suit your needs and that might be all your problem is.

Good luck with all that

Stevo

I think Studley is on the right track.

You don't say what size wheel you have - you should have an 8 inch wheel - the 6" has too much angle on it.

The best grinding wheels for HSS are white in colour - They are aluminium oxide.

Don

Hi Philly,

I had a similar experience and found it was caused by the nylon bush that came with the grinding wheel. I replaced the original bush with a better quality one which fixed the problem. I have been told that some guys turn-up their own.

Yep. I'm with Russell. Duff bushes sounds likely. Are they the same width as the wheel? Any slop? - test by pulling the cover off and push/pull at 180 degrees.

Or washer under the nut not bearing down evenly on the wheel.

Get a new wheel and put it on. Rotate it with the tool rest in place and see if it gets closer to the rest as turned. If so loosen of the nut and turn the wheel 1/4 turn lock the nut and rotate wheel again, keep doing this until the smallest amount of movement is detected between wheel and rest then repeat either way with 1/8 turn until wheel runs true or as close as possible. Lock the nut firmly for the last time and use a good diamond dresser to finish off. (you will get a truer dressing with a diamond dresser than with a block or star wheel dresser)

Your tool rest really needs to be rock solid for dressing as a flimsy rest can also help to put the wheel out of round and actually magnify the problem. When sharpening turning tools it is best to use the tool rest as a hand rest and grind freehand especially if the toolrest isn't rock solid.

Hope this is of some help.

Cheers - Neil

PS I only ever use the toolrest for sharpening a skew chisel that needs to have an new angel or bevel put on it and only for initial sharpening even then I will more often than not do it freehand, all sharpening after that is done freehand as is all my gouge sharpening, using the toolrest as a hand rest.

Doing it this way they never get hot and they always have 1 constant bevel without a lot of facets.

Almost forgot. I also had a set of flanges (the big washers that go either side of the wheel) specially turned for my grinders by an engineer, so they always run true amny of the cheaper ones are only pressed metal discs and can get a little out of wack. A little out of wack at high revs can mean a lot out of wack.

I also cut washers out of blotting paper and use these between the wheel and the flanges, they help to give the flanges better seating on the wheel.

What Neil said. Blotting paper being a fairly rare household item these days, you can also cut them out of thick kitchen paper.

Wow!
This one went off....

Thanks for all your replies. I did neglect to mention a few details didnt I?
I am using the correct white and pink wheels at about 60 grit, with a uni-jig, not a solid rest. I think the problem *could* be the bushes. Neil....I did indeed do the sort of thing you suggested and put a ruler across the wheel, leaning on the guard and spun the wheel and it does indeed make a rub at one point. I have tried dressing with one of those black blocks. Sometimes I have found this makes things worse (which could suggest Im pushing the wheel to a different point on the spindle if the bushes are loose?) Its very frustrating when the wheel hammers on the tool as sometimes it causes the tool to slip in the uni-jig which buggers up my grind somewhat. I find the plastic tightening wheel pretty flimsy on jig and the knurls are pretty non-existent. Maybe its time for a re-think! I'll get a diamond dresser tomorrow and let you know how it goes. Thanks again everyone.
Phil

Oh yeah....

Its an 8" wheel.

Phil, there's no point in dressing the wheel if there's slop in the bushes or the mount.

I was once sold a 1" thick wheel with 3/4" bushes; after dressing it would work for a bit but then run out of true.

(BTW The carborundum stick is for roughening the wheel surface so it's more abrasive.)