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Fw: [Unimat] Widening an existing hole with a drill bit: how to guarantee concentricity?

Bill in OKC too All Messages By This Member #59929 Steve pointed out to me that not all of my messages are going to the group, and he thought at least this one should, so here it is! 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! Improvise, Adapt, and Overcome. Physics doesn't care about your schedule. The only reason I know anything is because I've done it wrong enough times to START to know better. Expect in one hand, expectorate in the other. See which one gets full first. ----- Forwarded Message ----- toggle quoted message Show quoted text From: William R. Meyers <wmrmeyers@...> To: Steve Johnson <steve@...> Sent: Thursday, April 20, 2023 at 10:23:25 AM CDT Subject: Re: [Unimat] Widening an existing hole with a drill bit: how to guarantee concentricity? I have been known to make mistakes about what the OP was looking for, so I went back and looked at the original message. He has a chuck with a pre-drilled hole. I'm guessing that he didn't drill it, so doesn't have the drill. Besides, depending on the the drill, the setup, and how tight the chuck was tightened can all affect how big a hole a drill bit drills when it's used, so getting a accurate hole would be a crap-shoot. Sets of adjustable reamers are relatively cheap, so OP could ream the hole to size, Still be better done in his lathe, which he says is not all together right now... Maybe we need to find someone near him who can help him out! :)? 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! Improvise, Adapt, and Overcome. Physics doesn't care about your schedule. The only reason I know anything is because I've done it wrong enough times to START to know better. Expect in one hand, expectorate in the other. See which one gets full first. On Thursday, April 20, 2023 at 10:06:42 AM CDT, Steve Johnson <steve@...> wrote: Good point Bill. Still, providing the M12 hole had never been tapped, use the original bit for centering and bore with the new tap drill size.? On Apr 20, 2023, at 9:03 AM, Bill in OKC too via <wmrmeyers@...> wrote: 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! Improvise, Adapt, and Overcome. Physics doesn't care about your schedule. The only reason I know anything is because I've done it wrong enough times to START to know better. 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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