I made up two SS brake lines last week for a buddy -- for his new Wilwood master cylinder... they needed to be double flare to use his existing T block and Prop valve.... used my Mastercool tool -- they were perfect and didn't leak.
A couple of things - not sure how you're going about it from beginning to end - but here's what I do.
I only cut the tubing with my fine tooth body saw (tubing cutter will work harden the cut area)
I then square the end on my disc grinder (fine paper disc)
I then DEBUR the inside radius with a deburing bit on a drill
The "squaring up" on the disc grinder will turn the end (an 1/8" in) blue - that will re-anneal that end of the tube.
Then I do the double flare.
Looks like you may be clamping a bit "tight" as well...
Is the tubing you bought (are using) annealed?
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