double threading

How would a person go about tapping a sleeve so that the inside is 5/16X18 and the outside of the sleeve is also threaded at 18 threads and they match
at starting places as this female/male sleeve must be screwed into an opposing male/female fitting.
Dick
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cnc lathe
Dick wrote:

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On Fri, 08 Dec 2006 22:35:48 -0600, "c.henry"

SNIP
Hey C.Henry,
Not "simply". CNC will certainly do a thread, but not without substantial effort to get it "lined up" somehow.
Brian Lawson, Bothwell, Ontario.
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ours will , and its a rinky little nardini we make some threaded parts on a larger scale than what the o.p. is looking at and the threads have to be timed 90 degrees from each other , i dont know why but thats what the print calls for ,
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I've never done it, but what I would try is this: Make the sleeve and simply tap it. Run a 5/16-18 threaded rod into it with a locknut on it. Chuck it in the lathe and engage the half nut with the threading indicator zeroed. Line the lathe up on the threaded rod, turning the lathe over by hand and adjusting the threaded rod as necessary (be aware of the lash in the lathe...). When you have everything lined up, tighten the locknut. Now the lathe will be lined up horizontally on the bottom of the thread. Move the carriage (by turning the lathe over) to put the cutting tool over the sleeve and move in the crossfeed until it touches. Note the readings on the crossfeed and the compound (again, roll the lash out) and do a little math to figure how to set them so that, after you've cut the thread, the point of the tool is at the same place horizontally, but is now laterally at the bottem of the thread.
I hope this isn't too confusing. Just be aware of the lash in the lathe and you probably will need a good magnifier to get the tool lined up at the bottom of the thread on the rod. If you need to be really fussy, don't forget to allow for the slight movement (fit tolerance) the rod will make when you tighten the locknut.
Jerry
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Greetings Dick, Can you single point threads? If so then this will work: Machine to finished length and tap all the sleeves. Then put a piece of stock in the lathe and single point a 5/16-18 thread on it the length of the sleeves. This thread should fit the sleeves snugly. Finally, screw each sleeve on it and single point your 18 TPI thread on the outside. The parts will get stuck on the threaded mandrel because they will tighten up on it during threading. This means you will need to come up with a wrench to loosen them. If just a few parts a nut sawed in two and clamped onto the threaded sleeve with vise grips will work without damaging the threads. For nice threads use a full profile threading insert. You can either buy or make a tool holder. ERS
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Eric R Snow wrote:

Eric, in case I haven't mentioned it, YOU'RE A GENIUS!
GWE
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On Sat, 09 Dec 2006 10:13:37 -0800, Grant Erwin

Well thanks Grant. I really appreciate the compliment. Cheers, Eric
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Thanks all, actually this was not for me but another fellow who works on cues. He asked me how to do it and thought it would be easy to do and I told him I thought it would be difficult. Looks like I'm right. He thought he could just single point the inside and then the outside and they would stay in sink. I told him that wouldn't work as you would have to change tooling and that even if he ran the lathe in reverse for the inside threads and then kept the same tooling for the outside they would still be out because of the backlash in the lead screw between forward and reverse. I'll contact him right now so that he can review these answers.
Thanks very much, Dick
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Dick wrote:

Single-point both threads, with inside and outside tooling adjusted so that they cut at the same point (use left-handed boring bar for "normal" OD turning, bars have same length so adjustment is easy). Both threads can be cut the same direction, so the backlash is not important.
Could be done with normal OD thread turning tool with some effort to set the ID thread boring bar and the OD tool cutting point difference to be a multiple of thread pitch. Just put one tool to quick-change holder, measure, and then put the other tool to another holder and adjust the position vs the previous measurement so that the difference is a multiple of pitch.
Yet another way would to be use tap or ID thread turning tool to make the inside threads, then make a treaded holder for the sleeve, so that the sleeve is fixed to the thread same way every time. The holder needs to be fixed vs. spindle - could be between centers with driver centre/dog or at a chuck. Now, just adjust OD turning tool vs. the thread of the holder (before putting the sleeve in place), and turn the OD threads to sleeves one after another.
Kristian Ukkonen.
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An off the shelf possibility, if the available sizes are acceptable, would be a timesert: http://www.timesert.com
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OT , When you cant seem to create a small enuf thread ...
use a coupler nut , cut threads on outside that are diff by 1 thread in 20 feet ! Did i exagerate ?
You now have a differencial "incher" . Move one , one way and the other the other way , and the differencial will move something by microns !
But of course you must fine lap the threads ..
I have a book of mechanisms ..... fun fun fun ....
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