I don't know how work-hardened the copper tubing is
when you buy it. But, if it cracks as you straighten
it out, heat it to around 700 deg with a propane torch
to anneal it so you can straighten it. You'll have to
experiment & try a couple pieces to get the annealing
right.
If I remembermy metaurgy correctly? In order to anneal copper after
you heat it up to red color to soften yo then quench in water unlike
steel, which you slow cool to anneal. Jim A (that has been busy
trying to find a suitable replacement for the Mercedes that was
totaled by a suicidal deer on Sunday evening the 10th of this month).
No one was hurt but our dog seemed quite curious about the whole
adventure.