Grinding: under or over?

Well, like the Great Bathroom Debate, here is another controversy!

Adoring fans, I need your wisdom. In another post I was crowing about my new 180 CBN wheel from Carrols.

I've had a bit of a think (don't be rude!) and I thought what would be the best for sharpening chisels on the grinder?....wheel rotating towards you, or away from you (from the top of the wheels perspective)?

The default is so the grind is down, the sparks go down, but thinking about it, it would be better to reverse the grinder and have it so the grinds spit up and towards the back.

Keep in mind this is for turning chisels in a jig. It seems to me that the wheel rotating down onto the edge would be less favourable than the wheel sweeping from the back of the tool towards the front sharp edge.

Any thoughts?

Yes. Thinking. :think:

With the Tormek they recommend having the wheel turning into the blade when you want to remove metal quickly. For just touching a blade up have the wheel approach from behind the blade. The Tormek has both a vertical and horizontal position for the rest to achieve this.

Safer to use a pushing wheel rather than a pulling wheel.

When grinding an edge, you want the grinder pushing metal away from the edge, not towards it. I believe you get a cleaner, sharper edge this way, and that's why grinders are pretty universally made to turn toward the user, and a toolrest gives a solid place to rest the tool for this setup. I don't know how you'd do this with a reversed grinder.

This direction also means that if something catches on the front of the wheel, it's thrown to the floor, not the ceiling, which is much safer. Had this happen lots in the last few weeks, polishing small fiddly parts. :o

Now, a slow-speed water-cooled grinder may be a different thing? But I'd still want it pushing metal away from the edge for sharpening.

How "sharp" does sharp have to be for the application?
I've rehabb'ed a dozen Sorby lathe tools, freehand.
Days like that, I have visions of a variable speed, reversing grinder.

With the visible face of the wheel coming downwards, I can understand cutting/grinding metal away from the edge.
If the front face of the wheel were to be moving upwards, seems to me that the bevel edge would develop a huge wire edge in a hurry. That's not metal movement just metal that didn't get dragged off in the conventional direction.

Me? I'd select a really crappy chisel and try it both ways, just to see what happens. Always wanted to do that.
Maybe I got this all wrong. But there must be a good reason that the vast majority of grinders are set up as they are.

Like Rooster Cogburn said to Lucky Ned ( in the Coen Bros "True Grit " ) when Ned threatened to kill the girl......" Do what you think is best Ned! "

Quote:

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Originally Posted by Robson Valley

If the front face of the wheel were to be moving upwards, seems to me that the bevel edge would develop a huge wire edge in a hurry. That's not metal movement just metal that didn't get dragged off in the conventional direction.

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Ever tried to grate a zucchini? The leading edge of the zucchini gets nice and square, and the trailing edge ends up with a big flap of skin that doesn't grate off. :D

There are a number of very good reasons why the grinder wheel should always turn toward the tool.

Above all, you have far more control pushing the tool into the wheel.

All the well established grinding methods work because you have your weight behind the tool and can brace and push.

You have far far less controll pulling......I cant think of one single grinding application that would work well pulling...some would be outright dangerous.

The wheel should always rotate over the top toward you if it is a hard wheel.

IF however it is a mop, a rag buff, a wire brush or a burnishing wheel, you work on the part going away from you....mostly on the bottom of the wheel.........and that is a whole other argument.

cheers