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

[kingmt01]

Cigarette paper makes good cheap shim stock.

 

[Groundhog]

Or make a D Bit that is exactly the size you want. Drill the hole slightly undersize, then run the D Bit in. Google is your friend for making these bits. If you use O1 or W1 drill rod then easy to harden but would probably do fine for a hole or two without hardening.

I didn't know what a D Bit was when I read this. (I lead a sheltered life.)
So in my search I found this video;

that shows how to make one.

 

[Christian Poulsen]

OK my friend I have seen Journeymen struggle with precision holes (in "tents" LOL (.0002) in lathes with .0001 spindle runout and I have trained them so ifn' you want the skinny I will do so and a precision hole can be achieved with that .002 spindle runout by boring and some other tricks for both size and finish (provided the lathe (ways/carriage (yada) aren't giving you too much taper over the needed depth ("length) of hole and then that's when the reemer comes in with better results)...but the drill or reemer (1st with a dowel pin or drill blank in the chuck in the tailstock) needs to be on center to the spindle and there's tricks to that (adjustment) that need to be done IE This is why a guy will center drill, say a longer part (which will be on center with some careful easy handed high rpm center drilling (same principle as precision OD turning and ID boring will hold with that .002 runout) even with a tailstock set up that is out, but then, even in a precision lathe with no wear (taper), when he pushes the live center in and cuts the OD (X) he will cut a taper in the part...
holler ifn' you want me or need me to go step by step but 1st I will need to pop a top (or have a 2nd cup of coffee ifn' its before noon (LOL)...along the way and when done it will all be understood (you need a TEST indicator on a mag base plus a "round holder" (usually 1/8 to 3/8 OD) to hold the test indicator in both the spindle and tailstock (chuck)....again, these are thangs' that need to be learned and done when we're talking about .0001, .0002, .0003 but can be even in a somewhat sloppy lathe....cheers!

 

[kingmt01]

The way I did my chuck arbor in the lathe was to first make the threads in the end of a blank & face a nice flat shoulder. Then I screwed the chuck on the blank. I mounted a ground pin in my 4 jaw & indicated it to 0 runout. I mounted the drill chuck to the pin & cut the shank to size. I was very impressed that I get a repeatable .002" or less runout each time with that old worn drill chuck now.

For what your doing I'd approach one of two ways. I'd rather stick out enough stock to cut everything all on one setting. Face, drill, bore, move a center to it, turn the arbor to size, & then cut it from the stock. Flip it around, face & taper it for looks.

The second plan of attack would be to drill & bore it to size then mount the mill in the lathe & indicate it. Mount the holder to the mill & turn to size.

 

[Christian Poulsen]

I like your approaches (set up and operations) kingmt01 and I have done so....there are others ways and order of operations to achieve "tenths" (and most of anything in a Machine shop (smiley face here!)...
....except of course we must talk/teach more detail in the ops when dealing with "perfect" requested (IE "tenths") to trainees...
For example your above "...move center to it...." (the tail stock (with live or dead center) must be dead on center or all the X (OD's) and Y (faces) will be out...

 

[kingmt01]

Like I said, it's just two of the approaches I'd take.