necking/expanding thinwall aluminum

What you are attempting is called swaging. A three roller tool can be made to do this, but if you are looking for an extended length of swage on the tubng, relative to it's length, you may have to resort to a commercial swager. Torrington is one of the manufacturers. Unless you have a screw machine or similar lathe-type tool, I suggest the swaging machine for thousands. Standard cam rollers with the leading edge rounded off on a belt sander and buffed smooth work well in short swages. They are mounted in a triangular pattern in slotted adjust ment holes on a holder and forced over the rotating tubing or vice-versa. Good location control is going to be needed, and expect crinkled tubing until you get the learning curve downpat. Use lube on it in the rollers.

RJ

Thanks.

The finished product is 2.6" of 1/4" OD, 1.4" of 5/16"

I was thinking of a roller device like you said. I wish they were off the shelf.

I'll go back and try to do a more gentle two stage press with an internal support for the tubing. Maybe a Teflon sleeve.

I'll probably have a local shop do the first production run.

I would think necking up would be easier than necking down. A hardened and polished steel mandrel should be easy to force into one end of 1/4" blank chucked in a lathe. Should be easy with something like 3003 aluminum tubing. You might have to experiment with the mandrel diameter if your tolerance is tight.

Randy