Qt: [ The Greenfield rotating table is not super accurate.]
Brand spanking new a rotating table is pretty accurate with many scraped in but with a little wear they ae no longer as accurate as a ground-in magnetic chuck.
The ability to angle is very important for angle grinding and tweaking a small amount of angle so not needing to loosen a fixture and lose accuracy. One example is the needed adding roll (tilting down) the edge to add a secondary clearance to a stager tooth mill cutter. when you roll (tilting) down the cutting edge straightness of secondary land is no longer straight and the rotating table needs to be bumped a half degree or so. Yes, and then rolling up back to the primary land the table needs to be bumped back.
For example, a 6” mill cutter OD edge would be set .325" below center to get a 6* clearance, and then to add a 20* clearance secondary it would be set .720" below center. That change of adding more roll would make the intersect of the two angles look bigger on one side and not be parallel with the top edge so making a poor-looking cutter. The rotating table is bumped to correct this defect.
For grinding the cutting end of between centers ground reamers and going from primary to secondary this same effect happens and the table rotation feature is bumped perhaps a half degree to make the intersect land straight, for a nice looking reamer.
Another function of the rotating table is that often the rotating post under the table is offset, so rotating the table might give 2” additional distance from the wheel so adding capacity to the machine. Yes, one has to go far to one end with long travel to miss hitting the wheel head collum.
Best reamers are made and sharpened between centers, not out of a work head.
Also like a lathe whose bed becomes a little worn and so no longer turns parts dead straight, the grinder's rotating table can tweak a little angle to correct machine error.
If this seems confusing then one should free download the Cincinnati TC grinder operators manual and read it through as one would read How to Run a lathe.
Agree, any of the old-school TC grinder manuals have much the same but the Cincinnati manual is one offered as a free download...*but still send some bucks to Vintage Machine as a donation.
Cincinnati Milling Machine Co. (Milacron) - Publication Reprints - Cincinnati #1 Tool Cutter Grinder Operators Instruction | VintageMachinery.org