Jeff Liebermann wrote:

I don't read every thread.

Who does?

It's called "mitering":
https://www.google.com/search?q=mitering+bicycle+tubes
A mill with an tiltable head is probably the
easiest way to do it. I've watched the
process, but have never done it myself.
It can also be done with a lathe.

I do have a lathe, only I don't know if it
works. Maybe I can repair it. Getting the pipes
in place are probably easier with
a mill, right?

I don't know if a drill press will work,
probably not. Forget about using a tubing
notcher. If the metal is soft enough for
a notcher to work, then it's not strong
enough to ride.

OK.

Mitering bicycle tubes does not require
fabulous precision. A Chinese benchtop mill
could be used

OK, what brands are they?

--
underground experts united
http://user.it.uu.se/~embe8573