Or get a brake pipe bending tool..... really cheap from a decent motor factor, and avoids the risk of using heat or kinking the pipe..... mine has 'wheels' that support various diameter pipes.....
I have used an internal spring on the plumbing, but have never seen the external job, available for such a small size as well. I think I will try this, as I am working in a quite confined space. Thanks everyone.
cheapest/easiest is an 8mm external spring.No need for heat.bend it slightly more than needed then straighten slightly.This makes it easier to get the spring off.
I have used one of these for years, THE ONLY WAY TO BEND COPPER PIPE!
Using an external sping is OK 50% of the time. However a spring is not strong enough to always stop the kink. Then you finish up with a copper pipe with a spring stuck around it!