"jim rozen" suggested
If only a few thou of shrink is required, and the tubing is moderately
thin walled, one can do this in a (non-turning) lathe with a lever
type collet closer.

If you have access to a six-jaw chuck, you can do some nice "fluted"
neckings on thinwalled tubing. We use one to crimp shut brass tubing around
an electric match lead.

LLoyd