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The extrusion shape is a simple square tube. If I set it down on a perfectly flat surface with its curvature upwards, the middle raises up by around 5mm over the length of 1m.

So far I tried to just put a weight on it while its laying on a glass pane (my perfectly flat surface) but after 24h that did just about nothing.. maybe if I left it there for a year? I'm not that patient.

Are there any other options for me to straighten it without specialized tools? I could heat it up with a torch if that helps..?

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    $\begingroup$ In industrial circumstances, they are stretched while cooling, I believe - also not very practical for you. Have you tried setting the extrusion between two supports and flexing the centre down below 'flat', such that it springs back to the desired position? You will need to gradually push 1mm further every time until you find it is deforming permanently $\endgroup$ – Jonathan R Swift Apr 17 '18 at 7:00
  • $\begingroup$ @JonathanRSwift I can try that, going to have to rig something up to push it gradually $\endgroup$ – user81993 Apr 17 '18 at 7:06
  • $\begingroup$ You could also gradually increase a weight hanging on it, rather than gradually increasing the displacement? $\endgroup$ – Jonathan R Swift Apr 17 '18 at 11:42
  • $\begingroup$ Use a jack or screw thread to cause the deflection or, put the aluminium on two big blocks and lower a car onto it : worked for me in the past, careful with the lowering though... $\endgroup$ – Solar Mike Apr 17 '18 at 13:10
  • $\begingroup$ Seem to remember a technique which involves repeated heating the concave side with a torch. The differential expansion of the hot side vs cold side eventually corrected the curve... $\endgroup$ – BobT Apr 17 '18 at 17:45

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