How to prevent PETG from warping

I’m having issues with PETG warping. The products I make must be as close to 100% flat as possible once finished, but a lot of what I am producing seems to come out a little warped.

For background, my CO2 laser has a working area of 600x400mm, and I order sheets of PETG at 1250x2050mm. So when the sheets arrive I cut them down to size with a jigsaw, keeping the sheets as flat as possible while doing so, then store the 600x400mm sheets stacked on a flat surface.

I’m thinking that slight curves caused by the handling of the large sheets (possibly by the supplier), or inconsistencies caused by the jigsaw, or something to do with how I’m storing the smaller sheets in terms of temperature may be the issue.

Does anyone have any thoughts on this?

It’s quite possible that the sheets are produced by rolling, introducing anisotropy and uneven internal stresses that are released with cuts. Are the sheets warping before you cut them?

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I’m not too sure. it’s hard to tell as the sheets are only 2mm thick, so when they are laid on a flat surface they tend to take the shape of that surface. It’s only when I’m cutting them down smaller sizes (~12" wide) that the warping becomes apparent.

What would you suggest? A different brand or supplier maybe?


You may try preheating them before you cut them. What I mean by that is use a heat gun or maybe a heater and have them warm but not to the point that they are melting.

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Alternatively, I wonder whether heating and cooling them flat in a press would work?

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