Parametric two-part mold generator for OpenSCAD
by jasonwebb, published
A set of parametric OpenSCAD scripts that generate ready-to-print two-part molds from arbitrary STL models.
These scripts can be used to generate either square (with or without rounded corners) or circular two-part molds and are fully parameterized to make it easy to adapt for your application.
Refer to the instructions below for some general tips, as well ideas for casting.
I have successfully made casts from these molds using wax, Knox gelatin, Oogoo and chocolate. If you have success with other casting media, please leave a comment!
Many more pictures of molds and castings I made with these scripts:
If you'd like to read about the development process for these scripts, and learn from some of the issues I came across, check out:
If you really want to bring your molds to the next level, you can even try the "lost ABS" (or lost PLA) process to turn it into metal:
I have also uploaded a parametric open-face mold generator to create positive and negative molds:
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Prepare a model to create a mold from
To create a two-part mold using these scripts, you first need to prepare an STL model of your choice. OpenSCAD has some performance limitations when it comes to loading external STL files, so keep your polygon counts as low as you can. I like to use Meshlab's "Quadric Edge Collapse Decimation" filter (under the "Remeshing, Simplification and Reconstruction" section) to reduce the number of faces in more complex models to get them to load in OpenSCAD.
Avoid undercuts and overhangs in your model, as this mold-making process doesn't really allow for that.
Using the scripts
- Download one of the .scad files and open it in OpenSCAD.
- Update the parameters in the script to point to your model, as well as transform it to be suitable for printing.
- Compile and Render (F6) the script with your updated parameters.
- Grab an STL using the "Design > Export as STL" tool.
Guide to parameters
- Model parameters - external STL model to build mold around. Use the rotation, translation and scale parameters to orient your model relative to the mold.
- Mold parameters - attributes of the mold itself. Make it any size you want, and turn on or off rounded corners to help with printability.
- Key parameters - attributes of the registration marks to get the halves to fit together well.
- Pour hole parameters - attributes, translation and rotation of the pour hole so you can get material into the mold. This can be tricky, so take your time to experiment.
Slicing your mold
In my experience, the resulting OpenSCAD models are very tolerant of a wide range of slicing settings. I like to keep the infill down around 20%, and opt for only 1 shell, if any. A layer height of around 0.15mm works well for me. Larger layer heights can result in gaps in the inner mold form which can make it more difficult to cast.
Printing your mold
- Be sure to seal your bot against drafts if using ABS. I faced a lot of layer separation issues in the beginning.
- Make sure your build platform is level! If its not, you may see bowing or warping in your mold.
- Accurately measure the diameter of your filament and update it your slicing engine. I experienced some pretty severe delamination / layer separation issues on the outer walls of my early molds before I did this.
Finishing your mold
Depending on slicing settings, you may end up with a mold that is not completely watertight. I had small gaps in some of my molds that let water seep into the mold form and made it hard to cast anything. A quick spray or brushing of polyurethane fixed that right up for me, but obviously this makes any kind of food casting a bad idea.
Using your mold
After applying a release agent, use wood clamps or strong rubber bands to hold the two mold halves together. If needed, apply modeling clay to the seam just to be sure that nothing leaks out.
I have had very good success with using Knox gelatin to create flexible casts from my molds, but that is by no means the extent of what can be used. Here is a short list of ideas to try:
- Knox / Jell-O gelatin
- Hard candy
- RTV silicone (try Oogoo)
Try holding a small popsicle stick right in the middle of the pour hole during casting to create fun lollipops and chocolate treats!
Don't try to consume any of the castings you produce from these molds! The food safety of ABS / PLA is not really clear, so please just try to use these molds for experimentation, rather than food production.