Slow molding – sheet making

Continuing on Dave’s sheet press I made a mold for sheet making, suitable for the oven.

Basically a metal bottom with a heavy metal lid to press the melted plastic in the 5mm flatbar frame. Ones in the oven, some extra weight on top helps the squeeze the plastic in the mold.
For extra pressure I can tighten the nuts!

The first sheet is not completely melted, but not bad for a first sample

This is very helpful. Thanks, now I feel more comfortable to have a crack at this myself

Hey, Can anyone help continue this thread by providing some information on Plastic type + oven temperature + heat duration + cool duration?

This information is key and I have been searching these forms for a long time to no avail 🙁

I believe you can call that abstract art 😀

Hey @pimvb the productos look awesome.
Can you please share a bit of parameters? 🙂
(Plastic type + oven temperature + heat duration + cool duration)

I’ve done a similar mould inspired by yours and @procrastino but the results were terrible. See pics 😛

it’s very likely that the problem is because I mixed 2-3 types of plastics (PET and HDPE) which clearly have different behaviours (putting in the oven at 200° for 45min, PET was all burnt while HDPE was only starting to soften)

Thanks 🙂


Well, I had not so much trouble with sticky plastic.
You could check the “baking” time. Too long in the oven can make the plastic too sticky. Just a possibility.

Thoroughly cleaning the mold after using can make a huge difference.

And like procastino mentioned, oven paper could be a great help.
Never tried it but can imagine that it useful.



Yes! Made different products.

Slow molding – Clipboard

Check the “Share your creations” page 🙂

Share your creations


I’m so sorry for my slow response…

Hope I can still help you out by replying :-/

Your mold looks great. The mold I made works the same way and had good experience with it. I only had some difficulties with the metal sheet that started bending a bit after time, which had effect on the plastic sheet that came out. It was not super straight unfortunately. Especially difficult when you want to further work with it in lasercutter for example.

* I didn’t use anything to make unmolding easier. Didn’t had big issues with that to be honest. Sometimes the plastic was melted around the screw-thread or in between the flatbars. But most of the time I was able to remove it after some cooling down.
Sometimes there were some plastic flakes (probably another kind of plastic) that sticked to the mold. Thoroughly cleaning the mold after using with a spatula worked best for me. My experience is that every singel piece of plastic or plastic assessment remaining in the mold, could make it sticky.
Never thought about oven paper. Can imagine it it works fantastic!

* I did a lot of tests with changing the amount of plastic, the temperature and time. On the end I had quite a good idea about the right proportions and settings.

* Holes in the lid could work!
My mold just pushed the plastic out on the sides. But can image that a few holes works better 🙂


hi @pimvb, some time I have sticky issues with HIPS in compressions iron molds,
Making unmoulding difficult without breaking the mould, did you experiment with talk or any in-between agent to make unmoulding easy? As there is not many feed back on compression oven on the forum I m asking the question directly to you.
excuse my English!
Thank you.

@pimvb awesome work. any updates? what did you do with the sheets? some interesting products? 🙂

As I’m not receiving notifications of responses if I’m not mentioned, I try summon @pimvb with this… 🙂

Hi Pim!

I was just thinking if something like this would work… Great to see it does! 🙂
I put here what I had designed, the frame consisted on several rectangular bars, so that we could make thicker sheets adding more of them, and the lid goes inside the box, so that it could make more pressure and, maybe, more homogeneus sheets. What do you think?
Some questions about your device:
* do you think it would be posible to put some lubricant on the mold to make unmolding easier? Maybe a sheet of oven paper?
* I suppose shredded plastic takes more volume than melted… how do you know how much plastic to put into the frame to get an even sheet?
* Do you think it would be good to put some small holes on the lid to let the excess of plastic flow out?


Some other types pressed in the mold.

There is a relationship between the amount of granulate, temperature and time in the oven.
The blackish sheet was too long in the oven which made it a kind of caramelized on the sides. If I had used more granular, the corners would be melted too.

To prevent the sheets from bending, I kept them in the mold till it was cooled down.
Pressing it on a flat surface is also a possibility.

The mold turned out to work quite good and amazingly consistent.
I tried it with several different types of Polypropylene and polystyreen.

First with the 5 mm flat-bar frame, later with a 2 mm.
The last one appeared to be too thin and got damaged pretty quick in an attempt to get the plastic sheet out of the mold.

After removing the sheet, I cleaned the mold with spatula or even sandpaper.
Scratches caused by cleaning, became more and more visible in the plastic sheet itself.
Good to keep in mind when needing really proper and clean sheets 😉