I'm using a flare die, 37 degrees. I think the problem is in the tube prep. I was hoping someone out there had a system down; type of cutter, file used for chamfer, sandpaper grit for deburring? It's my understanding that the cracking is caused by improper deburring?
By using an acetylene torch it's quite easy, first blacken the end of the tubing by using acetylene only.
Next turn on the oxygen and heat the end until the charcoal is just gone.
Let the tube cool down gradually,when the tubing is cold it's ready to flare.
I have flared hundreds of solid lines and the process is always the same. In forming flares, cut the tube ends square, file smooth, remove all burrs an sharp edges sandpaper helps, and thoroughly clean. Use the correct size 37-degree flaring tool for the size of tube. The trick is to oil the flaring tool makes a perfect flare each time.
Cut the tubing with a saw. Tubing cutters compress the area where the flare is being made. When the tube is being flared, it will crack. Also, ensure the flare area is clean after cutting. No burrs or rough edges.
It would probably respond well to the process, but totally screw up the desired heat treatment compared to away from the flare. I agree with WKT, et. al. - lubrication is key.
