[handlewanker]

I'm not sure this is entirely true. On an R8, the straight portion of the collet/holder/whatever has a tolerance of 0.9490" - 0.9495" so right there is 5 tenths potential "slop" in that upper portion, and I am sure that the straight portion in the bore inside the spindle has a similar tolerance and undoubtedly a bit of designed in clearance. So there is not a "tight" fit there anyway and if needed, grinding another tenth or two out of that portion will have no detriment that I can see. The tapered portion of the tool would be able to "straighten" things out if re-ground. Indeed, a few years ago, Dave Decaussin of Fadal fame designed and made some very nice little CNC machining centers that used tool holders he called "Cat R8". These tool holders used only the tapered portion of the R8 and completely eliminated the upper straight portion of the typical R8 tool holder. Grinding that portion of the bore would pretty much just do the same thing and eliminate it from location the tools.

Look about 8:40 to see the Cat R8 tool holders.

https://youtu.be/b-y03hhCCME?t=519

Hi, I thought about that too and if the top straight section is clearance you won't need to regrind it at all......however if the bottom taper section is running eccentric then regrinding that part will work to correct it.

At a wild guess I would think that a die grinder on a small slide mounted against an angle plate and angled over at the taper angle would be a very doable DIY solution.....as Mac has said...….you only want to take off a few tenths at most and this won't affect the seating of the collet in the bore as it will only go back a few thou at most.

I would hesitate to suggest.....but if the Devil drives then it could be done...….. that a mounted grind stone in a die grinder, clamped against an angle plate and suitably dressed then moved against the taper with the mill table X axis to remove a few tenths, could work as long as the stone was long enough to grind the whole length of the taper in one move.

The stone would have to be mounted in the die grinder and dressed with a diamond initially to ensure it ran true.

One big factor and that is the draw bar influence on the collet...…...due to the end of the collet being a clearance in the bore, if the draw bar pushes the end of the collet to one side as it tightens you WILL get cutter run out as the cutter will run eccentric and more so the longer the cutter is.

BTW.....my opinion is...... the shortened collet of Dave D'C will not be supported as per a regular R8 collet, and as a cutter exerts considerable radial pressure when it is at a high feed rate the tilt over aspect would be a real problem......why then does an R8 collet have such a long length if it can work just as well as a cut down model?