Okay, I use the primochill tubing as well. Make sure your inserted core is clean and the tubing has been rinsed out well. So there should be nothing on both mating surfaces. As it heats and you stretch around a radius the force could be pushing any dust, etc. into the softened material. Also make sure you heat evenly, but slowly. Too hot to fast and you'll melt/create bubbles in the outer skin, but the inside wall will still be too hard. Too cold and you'll be stretching the outer wall. It doesn't look like it's too cold because your radius doesn't have any ripples or thin walls from stretching. There aren't any bubbles from over-heating. So odds are good it could be whatever you are picking up from the bending insert or from the tube itself. It seems everything sticks to those core inserts and I was constantly rinsing mine off from dust, cat fur, etc lol
It could also be a lubrication issue as well. because the insert may stick to the inside of the tubing, as both the tube and the insert heat up it could be creating a contact surface that isn't sliding as you bend the radius (smearing the surface). So having a bit of water in there from washing the tube/core could help break up the surface drag cohesion.
Last edited by Soulpatch; 01-23-2020 at 09:37 AM.