Design for Aligning Threaded Components

I am unable to visualise it, a rough sketch would have been good.

As far as I can understand - the solution may be a small locating step (shoulder) at the end of the threads (staring edge of the female and the last edge of the male) as the shoulders engage the alignment would take place.

Other ways may be with help of locating pins and shoulder screws.

How bout a union...

You could fabricate the part with the nose longer than necessary by a few extra threads, then use a master alignment tool to align the nose to the desired rotational orientation and then cut off the excess piece of nose. All of the parts would be aligned and trimmed using this same master alignment/cut-off tool so they would all be in the same orientation once installed and torqued properly.

If you want a back-up method for assuring alignment, you could use a second nut that you screw the nose into first (leaving it loose), then install the nose into the tube. Once it is in the proper orientation you then snug the second nut down, locking the nose into place.

A drop of a thread lock adhesive would hold everything tight.

You have had a couple good solutions already, but if you are in fact designing and machining these parts then why not design away the troublesome threaded joint all together?

Join them with possibly a boss, alignment pin, o-ring seat, etc, etc.

Tim

If I understand the application correctly, I would make the coupling such that one side has a nut that freely rotates about the one pile and the other pipe has external threads to fit the nut.

To keep the two pipes in correct alignment you only need to mill or cut slots in one pipe and corresponding mating tabs tabs in the other pipe.

The nut is threaded most of the way through, but leaves a step in the bottom that will butt up against the lip of the lower pipe.

Standard hydraulic fittings (JIC 37deg flare) do exactly what you are trying to accomplish. The cone in the fitting not only centralizes but also provides the seal. Have a look at how they are designed. Parker Hannifin is a good resource.

Yes that was one of the etc, etc, etc I was babbling about earlier. GA