Taint tryin’ to criticize ya Grigg, but if the flares are only decent as you say with the Fedhill tool, then it might be in the way your prepping the end.
I burned up probably 20 or 30 feet of tubing, making a flare, cutting off the sample and re-flaring it when I first got the tool just to verify that it was going to do what was promised. I’ve made literally hundreds of flares in both steel and SS 3/16, 1/4, 5/16 and have not had one single failure or marginal flare. Each one looked as good as the pre-flared tubing from the auto parts stores.
Rather than crush the tubing with a tubing cutter, I cut my tubes with a fine hacksaw blade. I then touch and rotate the end of the tube to square it up on a bench grinder that I have an 8"x1” 3m deburring wheel mounted on. I lightly de-burr the inside corner with an Exacto knife to remove any sharp corners.
Denny Graham
Sandwich, IL

Denny G
Sandwich, IL