Metric lead screw and nut

I need some help firstly in identifying a particular metric lead screw
then selecting the proper tap to make a suitable replacement nut for
it. The diameter of the screw is approximately 17.9 mm and the slide
it's in moves 2 mm for each turn of the screw.
I'm assuming that this would therefore be a M18X2 screw for which there
are taps available. Only problem is that the thread looks more ACME
than the standard thread type and nobody seems to sell ACME metric taps
even though I've seen ACME metric lead screws available. Any help would
be appreciated.
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Typically, the nut would be screwcut on a lathe rather than tapped. I would expect this to be a job that would take about an hour or so of shop time, using a HSS tool, rather than a tap which I would expect to have to pay several hundred dollars for.
You really need to find a copy of the specs for metric acme threads, too, to get the correct angles and depths to feed.
Cheers Trevor Jones
Reply to
Trevor Jones
No, not M18 x 2, but TR18 x 2. TR stands for trapez and is the functional equivalent for your ACME-thread (different angles etc.!).
Reply to
Nick Mueller
That's because you can't cut a thread profile like an Acme with a one-pass tap, you have to use a single point tool and progressively increase the cut depth.
I'm also no great fan of hand-tapping 18mm threads....
Reply to
Andy Dingley
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There is a metric trapezoidal thread with a 30 degree included angle, and there may be metric Acme threads with a 29 degree included angle. Be sure which one you have.
Acme taps, and I would assume ISO/DIN trapezoidal taps come in sets, or for relatively shallow holes like a nut, with steps, so you don't cut the full depth at one time. They ain't cheap, and most likely you will be ahead to single point the thread.
I have seen some of the old machinists do this and they use an angle plate mounted to a face plate and lots of indicator work. I am sure you could rig something like a short section of 1 inch bar stock to clamp in a 3 jaw chuck with a threaded hole to mount an angle plate to hold the half nut.
Reply to
F. George McDuffee
I've done it!
Admittedly, the tap was home made, 1/2"x 10tpi and had a three inch taper for a 1" through hole. But it is possible :-)
Mark Rand RTFM
Reply to
Mark Rand
These threads are discussed in Machinery's Handbook (pages 1807-1813 in the 27th edition; search for "trapezoidal" in the index of other editions).
Joe Gwinn
Reply to
Joseph Gwinn
Thanks for the replies. The nut material is Delrin and I'm thinking of going the homemade route too similar to this fellow;
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I have a spare lead screw that can be used to make the tap.
Mark Rand wrote:
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