On Monday, 7 March 2022 05:37:43 EST andy pugh wrote: > On Mon, 7 Mar 2022 at 02:08, gene heskett <[email protected]> wrote: > > The thread is not a tapered thread, measureing 12.95mm in the threads > > major diameter, and quite close to 1mm pitch, maybe .98mm? > > If the measurements are correct then it is not BSP either. > https://en.wikipedia.org/wiki/British_Standard_Pipe > (Which is the international pipe thread standard used everywhere > except the US, a metricated imperial standard) > > 1/2" Gas thread fits the description: > https://www.bodgesoc.org/thread_dia_pitch.html > (Or possibly a "Brass" thread which were all 26 TPI) > But seems very unlikely on anything made after the 1950s. > > Being pragmatic, I would run a die down the thread that I have a tap > for, and fit a Dowty washer, > What I am actually doing, is making a hose barb adapter, just tight enough to nake its own thread when convinced to screw onto it with a couple big crescent wrenches, with an O ring capturing champhor in the rear face to seal it up since the threads wont be other than what it cuts in the PETG. 2 .png's from OpenSCAD attached. Max pressure might be 5 psi, limited by these teeny diaphram compressors. Just 2 is all the mister needs, more would clean the cut better but 2 keeps to tool cold.
So far I've got one thats quite tight, and one .15mm bigger ID radius thats almost too loose, so one .05mm radius smaller is making now. It should need some effort to screw onto it, and have enough grip to flatten the O ring and seal well. There's about 8 threads engaged when assembled. And PETG is a lot tougher plastic than PLA. PLA would just sugar like herculite glass at the forces involved in cutting its own threads. PETG will yield and grip like hell. About 12" crescent wrenches needed. Or a pair of good metric box ends of 21mm and 24mm would be even better. Dunno if I've got metrics that big. Harder to find on my side of the pond. Our vehicles changed many years ago and that helps as the car parts places stock it all, just bring money in little red wagons, but everything else is stuck in jurrasic times over here yet. The sensors hex is 23.82mm, and my PETG is about 20.88mm. ID bore rad is 6.55 (minus the nozzle sqeezout of at least .4mm, so this one building should measure near 12.7mm ID, so the threads cut by a 12.92mm measured OD should be ok. Barring cold flow in te PETG, should hold till the rapture at least. Has anyone studied PETG for cold flow? I've never seen the term used on the same page as PETG. I don't believe I've seen any evidence of it in making by $10 harmonic drive. I'm not using a metallic hub in the armature, instead grinding a bigger flat on the notor shaft, and making the shaft hole .35mm bigger than the shaft with that bigger Dflat, and I've had no loose fit failures at the torque a 1NM motor can make. Some armatures have been driven onto the shaft with a small dead blow, and removed several times without getting looser after the original install. Thanks Andy. Take care and stay well. Cheers, Gene Heskett. -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis
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