How To Get A Perfect Fit For 1/4" Mills?

The correct size reamer will solve your problem. As for why anyone would make a 1/4" endmill holder, well if you have a machine with an obsolete spindle taper you may not have a choice or if you need an extended length holder to reach a spot where nothing else will.
 
I never saw much use for holders until I did a bunch of deep pockets. I have had heavy cuts pull an end mill out of a collet. Maybe it's my crummy collets, but an end mill holder solved the problem.
 
I would bore it and ball hone it to final size, yes its possible to get a small enough boring bar and bore a 1" deep 1/4" hole lots of tiny cuts bill
 
What size did you pre-drill the hole? Also if you stick the whole reamer shank into you chuck, it can be a bit rigid and not able to 'follow' the hole as well. I chuck on just abut 1/4" of the shank.
 
"Learn me" LOL, I'm not following "end mill holder"...are you making a collet (R8 or 5C or a specific one for one of the many specific Machine Tools out there?)...or a block or fixture to hold one to grind or sharpen?...or?
 
Endmill holder, as I understand it and have seen, is a tool holder that holds and locks the endmill in place wit a setscrew and goes into the spindle in place of a collet.
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Instead of throwing the old one it could you not just slide a sheet of shim stock in it to bump it over to the right place once tightened down to get rid of the runout?
 
OK I see and have used these (mostly for endmills that are bigger than a set of collets that go up to 3/4")...I see R8's for maybe a Bridgeport?...Still many questions and why's here but generally (and I see "perfect" in the title)....indicate the part stock or R8 (or whatever) blank) (prehard tool steel) dead on...turn, drill (undersize about 1/64 or whatever)...check and indicate again and then bore to size with a great finish (hopefully at least a 4 to 6 rms or better)...(using whatever ID gauge or instrument yoose' gots' to measure while "sneaking up" while boring)...use a 1/4" endmill itself for the final "go" gauge (you'll end up at about .0002 or .0003 over the endmill body dia. (and watch and make sure part is cooled down ("normalized") before the final passes...

...or, as said somewhere above and if your lathe? or mill? is somewhat "out": Do the above but bore to .248 to .249...then dull up the leading end cutting edges of a .250 reamer and run it through straight (hopefully not much if any runout)... and again use an endmill itself for fit...if it doesn't fit run the reamer through in and out until that endmill goes...(dulling up the leading "end" edge of a fin. size reamer is a key here to not going oversize in tenths...along with straight and rpm (slow!) and cutting fluid of course)

...or best is do the above boring but use unhardened tool steel and you bore leaving about .005 or whatever but you need a oxy/acytelene torch and a universal or toolpost grinder to grind the hardened and tempered (by colors (eyeball) rc55 -60) part hole to size (fit)...(and at least abraisive "paper" (if no bead blaster) to give (turn/spin) the part some TLC after torch/hand HT...

Note: Making this or similar use holders/parts should be made out of at least a prehard steel (or cast iron is OK but dirty LOL)
 
Oops and add ...Sorry, as I guess I often assume too much as I have boring bars I made out of carbide rod down to 1/8" dia and carbide "pieces" silver soldered on the ends and ground to bore, ID groove (for like small o rings) (even ID thread!)....that I would use for this 1/4" ID hole
 
I drilled 1/16th" smaller than .250. I made a 2nd one and used a boring bar i made , worked fine but i screwed up in the end and had to much runout.
I an putting the reamer in the tail stock to keep it strait with the head stock. I do not have shimms that small but i found by rotating the mill and checking for best runnout i could get it down to about .002"
This was mainly a training exersize for me. I have been using a drill chuck that came with the Unimat to mill and it is about .002" runout.
Thanks for all the ideas, Next time I will use them. Don
 
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