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



## dontrinko (Oct 14, 2016)

I am making a tool holder to hold 1/4" mills. This is my second try. On the 1st try I used a "1/4" reamer to make the hole for the milling bit. It ended up about .002" over size. The mill fits but with enough slop to produce a little runout.
  I measured the reamer and sure enough it is a little oversize. The mill bits are .250" and not under or over size.
   How do I make a perfect fit for the mill bit?   Thanks; Don


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## petertha (Oct 14, 2016)

I think you just need to buy the appropriate size reamer diameter. Depending on the supplier, they will come in 0.0005" increments & typically have a +/- tolerance on them, for example +0.0002" and -0.0000". Measure your shanks & then choose appropriate fit. Also examine the shanks for wear or marring, particularly raised features from set screw impressions. This can easily alter the fit. Avoid bottoming out reamers in the pilot hole, I've heard it can enlarge the hole from spec size.

reamer dimension ~0.25" example from Travers online catalog


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## Randall Marx (Oct 14, 2016)

I would lean towards boring the hole to get it exactly on-size.


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## Gerritt (Oct 14, 2016)

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.


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## Wreck™Wreck (Oct 14, 2016)

Randall Marx said:


> I would lean towards boring the hole to get it exactly on-size.


You routinely bore .250" +- .0005" holes 1+" deep?


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## kd4gij (Oct 14, 2016)

What is the purpose for a 1/4" end mill holder. A collet will run more true.


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## Gerritt (Oct 14, 2016)

kd4gij said:


> What is the purpose for a 1/4" end mill holder. A collet will run more true.


Why would it? A purpose made holder, made on the machine it is used on, will run truer than any collet. It all depends on how he makes it.
The purpose of the holder is to keep tools preset and ready to use. The tool length will be known, for use in CNC equipment. Much like QCTP tool holders.


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## Wreck™Wreck (Oct 14, 2016)

gerritv said:


> Why would it? A purpose made holder, made on the machine it is used on, will run truer than any collet. It all depends on how he makes it.
> The purpose of the holder is to keep tools preset and ready to use. The tool length will be known, for use in CNC equipment. Much like QCTP tool holders.


What he said.
If you do 50 tool changes per day you will see the wisdom of tool holders in an appropriate spindle, I would not trust an R8 spindle tool holder to repeat in the Z axis between changes. This is what cat and other design spindles are for, the holders may be grasped by an automatic tool changer as well


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## Chipper5783 (Oct 14, 2016)

A standard 1/4" reamer is 0.002" over?  You said the reamer was a little over - that seems like an awful lot.  Now, if it is just cutting oversize - that's another matter.

Are you following good preparation?  I generally drill, bore then ream.  Drilling is a roughing operation, the hole won't be round, straight or in quite the right location.  Bore the hold to get it at least straight and in the right location (if there are issues, make at least 2 passes).  I get it that this is a small, relatively deep hole - it does not need to be bored perfectly.  Just use a small end mill (say 3/16")  held in the tool post, position it so one flute is the cutting edge and go in as deep as you can.  Then the reamer will start well, if it starts well, it is likely to finish well.

Some materials don't cut very well.  I had some 3/8" holes to ream, and was working with some sort of mystery plate, seemed sort of hard - after 3 tries making oversize holes I quit.  I tried again with some regular mild steel plate, worked great on the first try.


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## kd4gij (Oct 14, 2016)

The cnc shop I worked used ER collets with cat 40 And tools where set in a pre setter. A high-end Weldon tool holder has the hole off centered by half the clearance so when you tighten the set screw the tool is on center. Most hobbyist aren't setup to do that. I asked what is intend use is because I do agree  that r8 collet don't repeat.


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## pineyfolks (Oct 15, 2016)

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.


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## Baithog (Oct 15, 2016)

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.


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## bfd (Nov 3, 2016)

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


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## Paul in OKC (Nov 3, 2016)

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.


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## Christian Poulsen (Nov 3, 2016)

"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?


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## Randall Marx (Nov 3, 2016)

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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## kingmt01 (Nov 3, 2016)

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?


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## Christian Poulsen (Nov 3, 2016)

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)


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## Christian Poulsen (Nov 3, 2016)

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


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## dontrinko (Nov 5, 2016)

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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## kingmt01 (Nov 5, 2016)

Cigarette paper makes good cheap shim stock.


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## Groundhog (Nov 5, 2016)

gerritv22 said:


> 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.


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## Christian Poulsen (Nov 5, 2016)

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!


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## kingmt01 (Nov 5, 2016)

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.


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## Christian Poulsen (Nov 6, 2016)

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...


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## kingmt01 (Nov 6, 2016)

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


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