Flattening warped acrylic

I have been making a lot of press-fit acrylic signs, but noticed one little problem… they warp after assembly. It’s not noticeable in some uses, in others it’s bad news.

I found that I could smash 'em flat with the heat press I use for making T-shirts, and it might work with a hand iron too.

  • Find a flat, heat-proof surface
  • Put your warped acrylic on the work surface
  • Cover your arcylic with a heat-proof teflon sheet or similar (I bet a silicone baking mat would work)
  • Warm your iron to ~180F
  • Put the iron on top of the acrylic–weigh it down if you can. (Not sure how important the weight is, but my garment heat press delivers even pressure and it sure does the job.)
  • Leave the heat on for about 15 minutes
  • Turn the heat off but leave everything in place until it all cools off, about an hour

To truly anneal acrylic you need a longer period of both heating and cooling, but this quick method has made my signs nice and flat.


Wow. The acrylic actually warped , eh? Surprising!
Your advise seems pretty sound. I wonder if just sticking it on a baking sheet and putting it in the oven at a similar temp would do the trick.

Seems likely. Some kind of weight on top would probably still help.

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Thanks for the post. I’m running into this on a larger scale. Using my GF to make some industrial toolings, and am seeing a big warp on .25" acrylic with heavy engraving on one side. Fortunately, this factory has a hot press. I’m going to give it a shot at your temp. Only concern is controlling the pressure, but I’ve been regularly putting these toolings in a 4 ton press, so hopefully it’s OK. To verify, the main point here is to let it cool under pressure, yes?

I guess the point is to let it cool while it is in the shape you want it to stay in. I think people do this without pressure too, with a flat sheet in an oven. I am only using a t-shirt press since I happen to have one.

One possible caution: even at these low temperatures, I have seen that acrylic softens enough to take a texture imprint. A smooth Teflon sheet left no mark, but the more textured rubber pad on the bottom half of my heat press did leave marking on the underside of an object when I did not use Teflon on both sides. So, be mindful of that, especially if you are using pressure.

Fantastic. I ended up just heating some heavy aluminum plates I had around to 83C and sandwiching my tooling between them as they cooled. Worked like a charm.