I am considering purchasing an MT5 to MT3 taper sleeve, cutting off the tang, and then boring the MT3 hole to accept R8 collets. My 13x40 lathe has a spindle with an MT5 bore, and I would like to be able to use R8 collets to hold things like the straight shanks of my expanding arbor set. I plan on building a draw bar and a plate to fit into the back end of the spindle hole to that I can draw the R8 collets into the spindle bore adapter. My hope is that by machining all of this on the lathe, I will end up with a very precise holding system for standard size round shafts that fit my R8 collet set.
As a newbie to machining, am I considering a silly solution to a non-existent problem? Is there an easier option? I can dial in round objects in my 3-jaw chuck, but I typically need to use shims, and the 4-jaw is a bit cumbersome to switch out and dial in, and the R8 collet solution seems somewhat trivial to implement. I have not been able to locate an MT5 to R8 sleeve but it doesn't appear that it will be too hard to machine.
Advice will be appreciated.
Post note: I just now disassembled and lubricated my 3-jaw chuck at which time I noticed that I had #2 and #3 jaws switched. Not sure how, as I am aware that it matters. Oh well, now they are within 2 thousands which was better than before and may now approach the accuracy of a collet? Anyhow, could it still be that a collet holder for the mill is still reasonable? Would it be easier to just make an R8 collet holder to fit in my 3-jaw chuck so that I can avoid having to remove the 3-jaw to use the collet holder? I could index the collet holder to the chuck to preserve accuracy...