Michael Black wrote in
news:alpine.LNX.2.02.1409161603130.29800@darkstar. example.org:

I've made short lengths of rigid, air dielectric coax for UHF projects
from hobby store brass tubing on several occasions.

That's true. For inside a chassis. And I suppose making rigid is much
easier than making flexible coax, since you can get that brass tubing.


I've never used it for that (not done much RF work at all), but I like it,
it's very precise (and in the UK and on eBay precision imperial sized tools
to go with it are often a lot cheaper than metric, and mixing units can offer
suprising answers to tough problems, like tight fits of 4mm into a 5/32 hole
or a bit of that tubing of same size ID (3.96875mm). (Which incidentally
might help answer the original question, as one way to make accurate DIY 4mm
sockets.) Brass brazing rods can also be used, they're supplied very clean,
straight, and with even thicknesses, and I suspect hard drawn quality too.

If I had to make a aired cored coax I might hard-draw a bit of stripped mains
cable by hanging it off the top of a door and putting my weight on it to pull
the other end. I have done that a few times and got very good straight copper
bars that way in thicknesses up to about 2mm diameter.