GlennW wrote: ↑Mon Feb 12, 2018 7:34 pm
The wheel grinds good after dress, (as far as surface finish) then gets real good, then starts to slowly go away.
Interesting. I wonder if you grind the same way I was taught? Just like in surface grinding, where you can take a large step-over but shallow depth of cut, repeating until depth is achieved, so, too, can one cylindrical grind that way. In fact, it's the prescribed method for internal grinding with through holes, but not necessarily for external grinding.
Finish was critical for the majority of the work we did, for the parts were generally quite small, and of high precision. Primarily, the mechanical parts of the guidance system. For that work, we used 100 grit wheels, aluminum oxide (38A), which did a great job. We, typically did our grinding by plunging at the headstock end, to preserve the corner of the wheel. We would then feed towards the tailstock to remove material, generally only one pass. We'd typically leave a few tenths for a finish pass, taken the same way. The periphery of the wheel, beyond the leading edge, did nothing but spark the part, improving the finish.
When grinding by this method, the wheel remains in pretty good condition, because the vast majority of the wheel breakdown occurs at the right corner of the wheel, to the depth of the passes being taken (the same way a centerless works in through feed). As the shoulder develops, it isn't necessarily a right angle, so as the shoulder progresses, it becomes a large taper, whereby the larger area in contact with the wheel starts to create grinding issues. At that point, the wheel would be dressed, restoring performance.
If, by chance, one uses the internal method of grinding, yeah, the entire perimeter of the wheel is in constant use, and it degrades more quickly, although I suspect that the difference in work accomplished per pound of wheel is about equal. I don't know that one method is better than the other, just different.
In my experience, the best possible surface finish usually occurred with a freshly dressed wheel. That could be more related to the wheel of choice, and the process we used. That, of course, was contingent on the wheel being free of imbedded particles---thus the typical feel of the wheel before picking up for a final pass after dressing.
H