Jesmonite is one of the easiest casting materials to work with in the market. It is a two part system product in which you mix a liquid part, called acrylic liquid, with a powder part, called mineral resin, in a certain mixing ratio to get the casting material. The material can then be poured into a mold of a desired shape. Once set, the casted part has an amazing look and a very pleasant surface finish, see for yourself in the picture below:
Enough talk about Jesmonite, let's get to the point: How to use 3D Printing with Jesmonite? Well, there are a number of ideas out there but we will touch upon the one that we have tried and tested. So, the idea is to create a 3D printed mold for casting Jesmonite; that's easier said than done. The problem is that jesmonite is typically casted in silicone molds, which being flexible makes it easier to remove the casted part once it has cured. With a 3D printed mold printed with PLA, the main problem is that both the 3D printed mold and the jesmonite casted part are hard; thus, extracting a casted part is very difficult. But nothing to worry about, we will try to show you how we did it step by step with an example.
Let's take the example of the following Christmas Tree Model on Thingyverse (Credits: https://www.thingiverse.com/thing:4669619):
STEP 1 : Download the model from Thingyverse
STEP 2: We need to create a negative mold of the model in a 3D CAD modeling software. Blender (https://www.blender.org/download/) is an open-source software that can do it fairly easily. First import the stl file of the model in Blender as shown:
Resize the cube (for a beginners tutorial on blender see https://www.youtube.com/watch?v=TPrnSACiTJ4) to enclose the imported tree model as shown:
Next select the box enclosing the tree model and then click on the Boolean modifier:
Select the ‘Difference’ method and choose the tree model from the dropdown menu. Then apply these changes to create a negative mold of the tree.
STEP 3: Split the mold into 2 or more parts depending upon the complexity of the model. In the case of our low poly tree example, splitting in 4 parts was found to be sufficient for easy removal of the casted part from the mold. In Blender, the bisect function in edit mode can be used to split the model into 4 parts. There are a number of good tutorials online showing how to do that (e.g. https://www.youtube.com/watch?v=HrszCAX5LEw).
STEP 4: Slice the different split models of the mold and 3D print. Combine the 3D printed split parts of the mold and secure then with tape, hot glue, or rubber band etc. The better the seal between the parts of the molds the less visible will be the seam line in the final part.
STEP 5: Mix the liquid and powder parts of jesmonite in the recommended ratio on the packaging. Pour mixed jesmonite into the mold and wait for 30 minutes to take the casted part out of the mold.
STEP 6: Take the mold apart and let the jesmonite part sit in open air for at least 24 hours for it to fully cure.
The final product should look something like this:
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