I need to straighten a piece of PEEK tubing to tight tolerances. Has anyone had any experience with this? The tubing comes in a roll of about 150mm DIA from the supplier which doesn't help and I've been really struggling to succeed at this. Tube is 1/8"OD X 0.0802"ID and I need a piece 270mm long with 1.5mm maximum permissible bow. I have many quite a few attempts and I can get it pretty close. See below what I've tried so far. They all involve heat.
1. Insert PEEK tubing into a piece of brass tube(perfectly straight) then heat up to 220C (maximum my oven achieves) and leave there for various different amounts of time: 15min, 30min, 45min, 1hr, 1.5hr and 2hrs. Remove from oven (whilst inside the brass tube) and let it cool back to room temperature. Result is a 5mm bow
2. Pretty much same process as above but leave the set-up in the oven then switched oven off and let the entire system cool down for 24hrs.
Results varying between 3 and 5mm bow.
3.Same as above but apply a torsional for on both ends of the tube. Tried many variations, half a turn, 1 turn, 1+1/2 turns, 2 turns.
Results are very inconsistent. I managed a couple of good ones with 1+1/2 turns but I cannot reproduce it. Tried more than 10 and got 2 good. This will be a production process and can't afford the material and time waste of a 20% success rate.
4.Built a jig that would force the bow to go the opposite direction then heat it up and let it cool. Went 'S' shape horribly.
5.Same as 1 but I used blocks on rollers to stretch the material while it was hot. Tried various different distances. Went up to 25mm stretch (which reduced the overall DIA by 0.5mm but that is fine for what we need it for). This gave me my best results so far but at 2.5mm bow and reproducible.
6.Started to think that I may need more heat. So I used a different oven to heat it up to higher temperature. Maximum I went for was 325 but still not solving the problem. It actually got worse.
Sorry about the massive post.
Can someone please save me?