In article ,
Michael Horowitz wrote:

This is not an aircraft repair.

I've got a piece of 4130 tubing, about 3" long, 3/4" dia and I'm
trying to slip it over a like size tubing.
Just because I'm trying to let friction do the holding, I'd like to
remove as little metal from the external sleeve as possible.
I made a slot in the tube and expanded it slightly with a wedge.
I though maybe heating the insides would cause it to open like a clam.

I could wedge it open and apply heat, thus deforming the tube.

Other suggestions? - Mike

At least for larger diameter tubes, you can buy a tubing expander from
Harbor Freight -- and they work!