TipLap style tool sharpener

[Toolmaker51]

Tony Foale's accurate comments triggered email new action in this thread; and of great interest to me. 5C is popular for many applications, and rightly so. Compact OD, with comparative large maximum bore, in more sizes than many realize, being OD threaded operable by a hollow drawbar, AND if selected carefully ID threaded for a variety of stock stops. New, they are available in roughly 4 price ranges.
Tony is correct that a 5C would hold a an ER setup nicely; and useful for tool or workholding as well.
Now for a little more on collets.
All that aside, an enterprising designer could build a replacement/ alternate spindle(s) for a spin-dex carrying ER's; utilizing more of a compression than collapse function. The compression feature permit range of closure of beyond the few thousandths of a 5C. 5C, R8, 2J, 215, etc are split in front only, sized and cylindrical at one particular diameter only. ANY other only pinch, which can also 'spring' the collet into deformity, and unreliable thereafter.
The brand I can't recall; but there was a grinder for larger drills using Jacobs Rubberflex, that also function ala collapse. They're tool steel fingers bonded to neoprene [?] spacers, very good work holding collets. The drawback is they need a handwheel about 10" diameter to operate. Too big for convenient sized T&C abrasives.
Another 5C advantage. Using the largest with an eccentric bushing will grind beautiful, tapered boring bars; the right way.