how much stock should be left for grinding.

how much stock should be left for grinding between centers also for centerless grinding.

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ALWAYS....as little as possible. Nothing better than just bearly cleaning up on the grinder....unless, there's some kind of surface your trying to get under or some kind of condition your trying to fix. Everyone wants a simple answer, and if that were possible, there's be no experts. The answer needs to come from experience. However, I realize you gotta start somewhere.
Questions to ask yourself: Is the part round, and if not how out of round is it going to be. Is the part heat treated, and if yes how much to get past the surface tension. What type of equipment do you have to work with.
First of all is roundness. usually a lathed part thats heat treated will be .001 out of round approx. Bar stock .002-.003 usually. Then there's bend. is the part bent? Or how much will it be bent when I grind it? Is it long or short(this is where feel comes in). Is the part heat treated, and if yes is it done in house or in a vaccume furnice? No heat treat, you better leave less stock, soft grinds crappy compared to hard. Was the part lathed, or is it bar stock? Is it hot or cold rolled steel, making it very stable in heat treat, or is it tool steel full of all kinds of nickel and chrome making it warp? Do you have to do it all in one shot with one wheel, or are you doing it production style. if you have the luxury of production(multiple pieces) leave more since you can be more efficient at stock removal due to multiple wheels, etc... Are you going to use a dedtrue centerless grinder, with a 6" diameter wheel on a 4" roller, or do you have a real centerless grinder, with giant rollers and a giant wheel. The big machine can eat stock a lot easier than a little dedtru, so you can leave more stock to grind on.
Easy answer...leave .005 on a diameter. .008 if your worried. But thats too easy, I sure as hell wouldnt leave .005 on copper, copper is so gummy it loads up the wheel.
Then theres cost. the big one. If I got 50 bux to grind a bar, id leave little. id have to gamble to make a profit. Now If im getting 1000$ to grind it, Id make sure theres plenty to clean up. Id leave extra just in case.
NO EASY ANSWERS. If it wasn't complicated, anyone could do it.
On a side note, do not grind anything between centers when a centerless grinder can be used. The roundness of the betwen centers way can only ever be as good as the runout of the spinner. Centerless on the other hand has no such limitation, plus its supported, and up against a wheel to suck out the heat. You can take twice the cut in half the time and get twice as good results. AND the most important part, when you dial down a .001 on a between centers setup, it removes .002 off the diameter. like a lathe. Centerless is one to one. You come down .001, it removes .001 on a diameter makeing this way of grinding twice as accurate, and half as likely you will remove too much.
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