Experiments with Sheetpress outcomes [#V4]

Hello Community, we are currently working on the development of the large sheet-press machine in version #4. Alongside we also started to experiment with the outcomes from it and also explore their different properties. So far it looks very promising and will open a whole different range of design possibilities. We are working with different types of plastic sheets like PP, HDPE, PS, Mixed etc. Here we will be documenting success and failure stories while dealing with them.

We are going to use various tools and machines for cutting, drilling, screwing, bending, welding and for trying different joinery techniques. The goal of this thread is to find out the most efficient techniques to work plastic sheets of different thicknesses.

For more information related to the sheet-press machine follow:


Constructive comments, suggestions, and ideas are welcome. Keep fighting and sharing.


                                                                         HDPE sheets

HDPE is definitely one of the most interesting and smoothly manipulable type of plastic to work on. After getting the HDPE sheet from our colleague and friend @markbertbach we started to experiment with different tools and joinery techniques with it. The material is super strong and almost acts like wood. It can withstand more strength and was a good longevity. But it is not so easy to make like other plastic, particularly PP.

The sheet we made is 1000mm x 750mm in size and 13mm in thickness. It was made with 10kg of black HDPE granule. The result has a very smooth finish, almost marble-like texture. It feels really tough and durable. It is extremely flexible. One can easily fold it in any angle with a half cut, without breaking or cutting completely.

The manufacturing process was not very easy. Because of its high viscosity, it takes a lot of time and effort to spread it after melting. We raised the temperature around 225ºC for the melting process. It created a high strength on the walls of the sheet mold and deformed it a little bit. The material is difficult to remove from the mold. It takes longer than making a sheet out of PP or PS.

I don’t have a CNC router but HDPE machines well on my small mill (much slower). You might want to try a router with a speed control box or a variable speed Dremel with the bits you want to use and run speed and feed rate tests on some HDPE cutting boards.

Hi all,

I am investigating making smaller, detailed jewelry using CNC Router and HDPE plastic.  I don’t have any of the hardware yet, so I am hoping that someone with experience in CNC routing can give me some advice regarding the success of fine milling with HDPE?

thanks for sharing, looks neat. Did you try flooding at the end ? I’ve seen this recommended quite a few times for polymers …  (i am still in good faith that we can build a plastic mill from plastic 🙂 )

CNC  milling PP Sheets

“Voronoi Jewelry”


Objective: Exploring digital fabrication, Making a Jewelry.

Material: recycled PP sheet (5mm thick)

Software used: Rhinoceros, Grasshopper, Autodesk Fusion 360

Tools: CNC milling machine, 1.6mm dia tool bid

Machining time: 25 minutes

Post-processing time: 30+ minutes


o   3D modeling and tool path creation were similar to the previous method.

o   PP did melt at the edges due to the rotation friction of the tool bid.
o   Had to constantly blow air to remove the particles as those were getting attached to the tool bid and the material often.

o   It took a lot of time and effort to post-process the outcome with a normal cutting blade to remove the extra particle attached to the edges.


o   It melts at the edge due to the friction with the tool bid.

o   No bad fume while milling.

o   Requires special attention at the time of milling and post-processing.

o   It is time-consuming to remove the extra particles.

o   Not so recommended for laser cutting also as it melts easily (in my opinion).

o   Not so happy about the outcome as it feels quite light and plasticky.

right, sounds like a reasonable recommendation to the non-skilled audience; I am placing your post in the library. I think a ~500$ can do still good stuff : cut raw stock and create molds (plaster/expoxy); I don’t know the controller software for these machines but let’s say it’s not Mach3 (another 100E) and something customizable/extendable (as smoothie board firmware)  then we could have a good option for the average budget of ~2000 – 3000 in total. Technically the router can be used for printing as well.

Hello @pex12
I machined the small parts you see up in the picture there.


So for laser cutting i heard from an experienced member that it is quite hard to process recycled materials due their non homogene material structure. I never tried it myself tough…

For the CNC machining part you can probably use every machine on the market, especially in those small dimensions. If you never used a CNC machine before, even the 200€ machine can be a good starting point. If you know already how those machines work i would recommend you to start with a chinese 6040 CNC or similar machines above 1500-2000€. This will enable you to have a reliable machine, which is not granted on 200€ CNC machines or Shapeoko builds.

You spend often much time on fixing stuff and re-adjusting your machine.


In this setup I used a single flute(very important for all types of plastic, because everything else melts the material!) 1,6mm endmill with air cooling (optional, depends on the speeds). You could machine the part much faster if you optimize your clamping strategy for flat, thin parts and work out different tool parameters.


The parameters were about ~600mm/min at 24k rpm and 1mm depth – mostly contour cutting.

Hope this helps 🙂

according to google results, it is best to cut it under a water/cooling flooding, especially harder stuff … did anyone tried a laser yet ? i think there was something about, technically clear plastic should be fine though.

On my small mill, I have not established a convenient way you collect all the chips for remelting so they tend to get vacuumed with other dirt and end up as micro plastic in the trash. The lathe is easier since it produces continuous swarf.

If you have a good solution for this, please post a description.

thanks for sharing; 20 mins. for this little thing seems overly long; did you try faster?  And could you add some details about the used mill (2, 3 or 4 flute), as well about the speed and feeds, step-over, etc… ? I am also wondering this can be done by a small Arduino/GBRL machine (Nema17 , SBR rails and for those who like it ‘sustainable’ : a frame from beams …). There are ready to machines starting form 200$ That would be an ideal candidate to extend PP’s official portfolio and processing recommendations when it comes down to mold alternatives (2nd or 3th most searched PP content according to my numbers); ignoring the fact that there are many unable to use this kind of machines 😉

CNC  milling HDPE Sheets


Objective: Exploring digital fabrication, Making a recycled plastic coaster.

Material: recycled HDPE sheet (5.5mm)

Software used: Rhinoceros, Autodesk Fusion 360

Tools: CNC milling machine, 1.6mm dia tool bid

Machining time: 20 minutes

Post-processing time: 15 minutes


o   I used Rhinoceros as the modeling tool and then prepared the tool path in Autodesk Fusion 360.


o   Machining time was pretty fast. As HDPE does not melt at the edges due to the rotation friction of the tool bid, it did not require any additional cleaning to run the machine smoothly.

o   Gave the final output a run with a normal cutting blade to remove the extra particle attached to the edge. But this HDPE sheet hardly took any time for that process.


o   It does not melt at the edge due to the friction with the tool bid.


o   No bad fume while milling.

o   Almost feels like milling a wooden plank.

o   Leaves a little bit of plastic dust at the edge, but it is really easy to remove with a regular cutting blade.

o   Highly recommended material to use CNC tools on.

Hey, I haven’t tried using PLA for making sheets. Mostly using HDPE, PP or PS. But will like to see your outcomes and research.

I have a project that i want to use sheetpress for. It is for pressing completely clear PLA pellets into .125″ sheets have you tried the plant based plastic PLA. i know it isn’t recycling but still.

Drilling and Screwing HDPE Sheets


Objective: Exploring screwing and drilling techniques.

Material: HDPE

Tools: Electric drill, Drill Bids, Thread makers.



—  Drilling and Thread making.

o   It drills a hole without making any crack or melting the edge.

o   Both 9.5mm and 2.5mm diameter thread makers made thread smoothly.

—  Screwing.

o   Making a hole with the drill before screwing makes the work easier.

o   I tried putting screws at a different distance from the edge [2.5mm, 5mm, 10mm, 20mm]. All works good, even putting a screw at a distance of 2.5mm from the edge didn’t crack the material.

o   Putting a screw straight without pre-drilling the sheet can be a bit difficult.


o   Very smooth material to drill a hole.

o   It does not melt at the edge while making threads with thread makers.

o   Easier and better than drilling or screwing a wooden plank.

o   Screws can be used easily as joinery elements for this material.

Still . . . looking at your display up top, it’s almost like going into a store to shop for a stone for your counter top.  I want to run my fingers across the surfaces.  The light touches of secondary colors are I think an important touch.  Getting into that range where it may not be a naturally formed stone, but it’s close enough to fool the eye and allow the artistic sensibility of the designer or end user to flourish is very compelling.   The piece that you worked above has a depth of color I’ve had difficulty trying to produce, that illusion of greater depth than the source material.  It’s like an oil painting almost.  If you can be where you are afraid to cut it for fear of ruining the original piece, you are now confronted with the artists dilemma instead of the craftsmans grumbling.  A far cry from a pile of garbage isn’t it?

We still have to experiment with greater thicknesses, but I have my doubts towards reaching 4-5 cm with the sheet-press process. I think we’ll reach a limit enforced by the heat transfer coefficient. Maybe with mixed processes, e.g. extruder + sheet-press, we can reach these greater thicknesses. Other ideas are to weld sheets together, by melting 1 side of the sheet en then pressing two sheets together, forming plastic welds. This could be used to extend the length and width and hopefully also the thickness.

Warpage is a recurring problem that indeed increases with scaling up. nevertheless, we’ve been able to get nice results with manageable warpage.
well balanced cooling, evenly throughout the entire surface and equal on both sides seems to do the trick. It is also important to let the entire sheet cool down under pressure or at least while restricting the warpage.

As to suface finish, the mould finish will copy onto your sheet, so spend a day polishing and your sheets will come out shiney, but for the stool in the picture a structured surface finish was created by using structures ptfe foil

in the other pictures you can see the flatness/straightness of a sheet of PP 105 x 75 x 1,2 cm

Quite impressive.  Do you think that you are close to something that you could market as say a countertop?

With much more rudimentary forming than your sheetpress, I had difficulty with stock warping when I’d attempt using a planer or router on formed #2 hdpe.  I’m pretty sure that I could bang together some 6″x6″ tiles out of #2 HDPE and glue them down with some variation of the polystyrene glues.  But beyond a certain size there’d be too much warping with what I’ve done.  I also had very matte finishes, not exactly the sort of thing that I really wanted.  That press has yielded some progress.  If you can get to yielding something around a meter deep, 4-5 cm thick, and can hold form in excess of 2 meters wide, then you have yourself a product.  Then lets see about coming up with invisible joinery or seams.

I’m kinda jazzed looking at what you’ve done.  Very cool.

Cutting HDPE Sheets

Objective: Exploring different cutting tools and techniques.

Material: HDPE

Tools: Jigsaw, Mitre Saw, Table saw.


I used Jigsaw with plastic cutting blades. Continuous push and faster movement result in a smoother cut. Blades with different orientation of teeth gives different output. Because of its high density, the blade might get stuck in the material if moved slowly. Leaves decent finish after cutting, but needs sanding for a better result.

o   Using Mitre saw was a great success. Plastic cutting blade works perfectly. Faster you run the machine smoother the result is. HDPE leaves only a bit of plastic dust due to cutting but no melted or sticky plastic on the machine. The dust can be removed easily. The finishing of the cutting edge of the plastic is already quite nice.

o   Table saw worked the best because of its speed. Using Plastic cutting blade is a must. It made a very smooth cut. No fume or melted plastic on the blade. Perfect for the big piece of sheets.

The result generally does not require polishing after cutting it.

o   It does not melt at the edge due to the friction with the cutting blade.

o   No bad fume while cutting.

o   Almost feels like cutting a wooden plank.

o   Leaves a little bit of plastic dust on the machine, but it is really easy to remove as it is not sticky.

o   The faster the better. Table saw and Mitre saw gives smoother output.