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Thin walled tube threading

Thin walled tube threading

Thin walled tube threading

(OP)
I have an 6061 aluminum tube (1"OD x 0.058" wall) that requires an end cap on one end and a retaining ring on the other to keep parts inside. The tube is turned down to 25mm OD and anodized for use as a linear shaft. For the past while we've been having the end caps welded in place, then turning the tube to size. We would like to move away from welding for a couple different reasons.

The end cap is subject to axial loads of up to +/- 200 N, high vibrations, and an operating temperature range of -20° to 70°C. I'm trying to figure out if threading the tube and end cap is a suitable alternative. CNC single point threading is the preferred method of manufacture and they would be assembled with permanent thread locker.

Say I spec'd a thread with a minor diameter equal to the ID of the tube and a thread depth of ~1/3 the wall thickness. Is it sufficient to choose a thread engagement length that results in a thread shear area able to withstand the loads by some margin? How do I go about determining the effect of the cyclic loading on the threads? Is anodizing such a fine thread kosher, or should I mask off the threads before anodizing?

Thanks in advance for any help on the matter!

RE: Thin walled tube threading

You could probably swage the end of the tube to a smaller OD, forcing the ID small enough to retain internal parts, depending on the design.
Or curl and/or fold the end over like a shotgun shell is closed.
Or emboss a ring near the end of the tube over a plug with an annular groove in its OD. I think this can be done with electromagnets with impressive speed. Or mechanically with a roller.

If the closed end of the tube needs to be watertight, consider forming the whole tube by impact extrusion from a thick disc.



Mike Halloran
Pembroke Pines, FL, USA

RE: Thin walled tube threading

Try shaft-locking compound and a close slip fit. No need for threads.

RE: Thin walled tube threading

yoketech,

I think that any finish on your threads other than anodizing, is not kosher. Aluminium galls.

--
JHG

RE: Thin walled tube threading

Use the same technique used for push-nuts or Legris fittings.

RE: Thin walled tube threading



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