Re: Widening an existing hole with a drill bit: how to guarantee concentricity?
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Are you sure about that? The tap drill for an M12x1 tap is 11mm. That is what I used making the collet chuck and faceplate that I worked on. Both fit the Unimat SL spindle. See the Metric fine thread chart here:??I am a bit math-challenged, but that should make the minor diameter 11mm or perhaps a bit more. If it were M12x1.5 or M12x1.75 you'd be closer, but probably not enough to get good concentricity.?
Bill in OKC
William R. Meyers, MSgt, USAF(Ret.)
Aphorisms to live by: Good judgement comes from experience. Experience comes from bad judgement.? SEMPER GUMBY!
Expect in one hand, expectorate in the other. See which one gets full first.
On Thursday, April 20, 2023 at 09:54:10 AM CDT, Elliot Nesterman <elliot@...> wrote:
Without a milling machine or a lathe, achieving perfect axial alignment
will be difficult if not impossible. You can get close, or even perfect
if you're lucky, with a drill press. Drilling by hand you will ruin the
collet chuck.
Drills are not precision instruments. They like to wander, even once
they're in the bore. Guiding a drill by hand to achieve perfect
alignment of any sort is not possible, at least not to machinists'
tolerances.
The minor diameter of M12 is 10.106mm. This is the size of pin you would
need to set the alignment with the drill's quill. A 10mm pin will still
allow 0.1mm, 0.004", of slop. And it's likely that the minor diameter of
the chuck is a bit larger, to ease threading on a spindle nose.
Also, the drill bit should be as short as possible. Drills flex. Using a
screw machine bit (stubby bit) will help.
And, of course, you'll need to find a way to fixture the collet so it is
immobile once it's aligned and on the drill press table. The usual kind
of drill press vice does not hold round objects in a vertical
orientation very well.
Still, as you can find M14x1 collet chucks on Amazon fairly
inexpensively, you won't be out much if the enlarging doesn't work out.
Best of luck.
--
Elliot Nesterman
elliot@...
www.ajoure.net
"The finest jewel cannot disguise a flawed character."
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Bill in OKC too