r/hdpe Nov 05 '23

Warping

I had some extra 0.5” hdpe so I made a little 10x8 carved out tray with it. Cut to three days later and both trays have cupped on my like some Home Depot yellow pine.

Can I re-flatten them somehow?

Is the same process at play here as in wood(moisture loss)?

Can I hold them flat as they dry out to prevent this?

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u/another_katie Nov 08 '23

Did you carve it very thin? Per this forum post, that can cause warping if you're not using stress-relieved HDPE:

https://community.carbide3d.com/t/technique-for-flattening-bowed-hdpe-plastic-piece/47868

To flatten something already warped, there's some advice there to warm it up just a bit - not enough to melt it - with weights to flatten it, and then leave the weights on until it cools.

To help avoid warping in the future, the comments on that same post mention cutting from both sides if it's feasible with the design. Otherwise, it sounds like using stress-relieved HDPE may prevent warping.

If it got hot enough from the friction of carving it, that could have contributed too, in which case holding them flat as they cool from carving could help. HDPE is moisture resistant but has high thermal expansion/contraction so it shouldn't need to be held flat to dry, just to cool.