Minimum wall thickness for stainless steel tube

[tgun829]

Hi

I’m working on a project. I’m considering to use off the shelf stainless steel tubes with 13mm OD and 11mm ID. That gives 1mm wall thickness. The idea is to lathe the ends of the tube, then thread them to make male and female. Thanks for your help in advance.

Todd

 

[JimDawson]

If you threaded the ends at M12x1 that would give you 0.5mm wall at the threads. Or you could make them 1/2-20 or 1/2-28 and get a little more wall.

Would it work for your application? I don't know. How much wall strength do you need at that joint?

 

[RobertB]

Would it work for your application? I don't know. How much wall strength do you need at that joint?

That is the question, without knowing the application it is hard to give a good answer.

Is the strength of the wall or the strength of the thread more important? There are examples of much thinner wall tube being threaded, for example the brass tailpiece on a sink drain. If they are just threading together you don't need a standard thread, you could use a very fine shallow thread leaving plenty of wall thickness at the expense of thread strength.

 

[whitmore]

I’m considering to use off the shelf stainless steel tubes with 13mm OD and 11mm ID. That gives 1mm wall thickness. The idea is to lathe the ends of the tube, then thread them to make male and female.

That'll be difficult; the 1mm wall is going to have to stay rigid when you apply the cutting tool. An external
(collet) support can hold it for internal threads, but some sort of internal support (a mandrel, or
maybe fill with low-melting alloy)
would be a good plan for external threading.

Tapered threads (sounds hard, but it isn't) are tolerant of minor dimensional mismatches, and you can do the
internal thread without having to undercut the tube at the max depth.

 

[nnam]

I don't think you can use that same size as male and female, unless the thread is very fine, so you would cut both tubes thinner. A larger female may work to connect them. A section of larger female connecting two male works also. Will it be strong? It depends what it's for. Brazing larger ends that have threads (male and female) can be both strong and work.

 

[nnam]

Also, flare coupling like brake lines work great too

 

[Downunder Bob]

De[ends on what you are going to do with them. Is the ID or Od important to be smooth and at constant dia. How much strength is needed, is internal pressure involved. we need the full story to advise.

 

[RJSakowski]

Hi

I’m working on a project. I’m considering to use off the shelf stainless steel tubes with 13mm OD and 11mm ID. That gives 1mm wall thickness. The idea is to lathe the ends of the tube, then thread them to make male and female. Thanks for your help in advance.

Todd

With both internal and external threads fitting within the 1mm wall thickness, you will want to use a custom thread. For more or less equal wall strength, the pitch diameter will need to be around 12mm.

I would use something like a .5mm pitch which would have a major diameter of 12.36mm and a minor diameter of 11.71mm. Going to a 1mm pitch would yield a major diameter of 12.65mm and a minor diameter of 11.54mm.

This would be for perfectly formed threads. Cutting tools with a radius smaller than the standard thread profile will produce slightly thinner walls.

 

[RJSakowski]

If you don't want to single point the threads, 1/2-48 taps and dies are available. This would be the equivalent of an M12.37-.53mm.

 

[tgun829]

That is the question, without knowing the application it is hard to give a good answer.

Is the strength of the wall or the strength of the thread more important? There are examples of much thinner wall tube being threaded, for example the brass tailpiece on a sink drain. If they are just threading together you don't need a standard thread, you could use a very fine shallow thread leaving plenty of wall thickness at the expense of thread strength.

The strength of the thread is more important. Yes, I was thinking about finer thread. In fact, for my application I really don't need more than 2 to 3 threads.