The original art sculpture for my giant walnut was created digitally using Maxon Cinema4D modeling software. Silicone molds were then made using 3D prints as masters. The finished casts are made of "Water Putty", a plaster-like material. A special "Nut Filling" hides inside!
This was my first time making silicone molds. I found some helpful information and tutorials on Evan and Katelyn's YouTube channel, along with the Smooth-On channel. (YouTube links below)
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Step 1: Tools and Materials
Some of the tools used in this project:
Some of the materials used in this project:
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Step 2: 3D CAD Modeling and Digital Sculpting
To start with, my goal was pretty simple. I wanted to create a super-sized walnut shell that could be cracked (or smashed) open in a realistic manner to reveal something inside. I wasn't quite sure what the finished dimensions were going to be, but that detail wasn't immediately necessary because I was planning to make a digital sculpture. This polygonal model, as long as it had appropriate detail, could be re-sized after it was finished.
I had several real walnuts to use as reference, so I got to work (virtually) carving the nut shell with all the little bumps and crevasses that make a walnut look like a walnut. I use Cinema 4D for polygonal modeling, but there are several other apps that can do digital sculpting. For the sake of proportion, I modeled the full nut, but I really only needed one half of the shell for 3D printing.
Step 3: 3D Printing the Shells
I was now ready to make my virtual nut into something more tangible that I could hold in my hands. I decided to print the model at a size that could fit on the build plate of my Makerbot 3D printer. I made the half-shell approximately 4.5" x 6" x 2.25". My plan was to be able to mold two nuts at a time, so that required four half-shells. Each one of these took about four hours to print.
The 3D model is available for download on my web site.
Step 4: Developing a Recipe for the Casting Material
I did some experimenting, so you don't have to!
Here is what I learned:
• Water Putty is AWESOME and inexpensive. Mix it thick or thin. Hardens great, either way.
• Water based acrylic paint works great to add color.
• Too much sawdust is good for texture, but will weaken the putty. A 1:5 ratio (or less) works good.
• Becomes quite hard, but does shatter when hit with a sledge hammer.
Step 5: Prepping the Master Models
Most desktop 3D prints, especially FFF (Fused Filament Fabrication) types, will have visible layer lines. For most intents and purposes it really doesn't matter. In this project I wanted to smooth out the surfaces. Typically I would prime - sand - prime - sand several times. This technique usually works well, but these nut shells have so many bumps that I knew sanding would be very difficult. I opted to just apply many coats of thick primer. It worked pretty good.
Step 6: Preparing the Mold Boxes
I came up with dimensions for the mold boxes that would be as economical as I thought practical, in order to use the least amount of silicone. I found a couple of old particle board shelves to up-cycle. It turned out that the smooth melamine surface worked great. I cut all the pieces on the table saw.
Step 7: Building the Molds
I decide to build the boxes with screws to allow for easy disassembly. I found another economy! By adding some small wood triangular prisms, I could further reduce the volume of silicone needed.
The nut shell models were hot glued to the base board. This allowed a small amount of silicone to sneak under. This would give me a more finished edge at the seam where the two shells meet.
At this time, I also gave each mold a quick dusting of mold release.
Step 8: Mixing the Silicone and Pouring It in the Molds
Making molds is all about volume. Even when a material has an A:B mix ratio by weight, we still need to know the volume in order to prepare the correct amount. The package of Smooth-On OOMOO 30 is only marked by weight. I had to refer to the enclosed data sheet in order to determine the volume. My "OOMOO MATHS" images show how I figured it out.... AND IT WORKED!!
It cannot be over stated that mixing thoroughly is very important. That includes mixing each of the components in their own respective containers BEFORE combining. Remember your working time is limited. So, be prepared!
I implemented the advise to pour slowly when filling the molds. This worked great. I ended up with very few bubbles.
Step 9: The Cured Molds Were Ready to Use
After six hours of cure time, I removed the screws and revealed four beautifully detailed molds. I was impressed!
They were ready to use immediately, so I moved on to mixing up the Water Putty, adding my colors, and walnut sawdust. I slowly added water until the mixture was like stiff cookie dough. I pushed it into the molds so that the walls would be about 1/4" thick.
I then set them aside to harden. Water Putty takes about an hour to firm up, but it needs about 6-8 hours to fully harden.
Step 10: De-Mold and Clear Coat
When it was time to take the shells out of the molds, I was pleasantly surprised at how easily they came out. By the way, I used no mold release at this stage.
I filed the edges a little with a wood rasp, just knocking down the high spots to get a good fit between shells.
I added a final satin clear coat. That brought out the color and gave a nice soft and subtle gloss.
Step 11: Add the Filling
These nuts are meant to be cracked, so I wanted to be a little goofy with the insides. The filling consists of real fresh walnuts nested in Walnut and Cedar wood shavings.
Now I just need to find a Nut Cracker big enough to do the job properly!
Step 12: Go Watch the YouTube Video!
I hope enjoyed this Instructable!
Do you like my work? You can also find me on other social platforms!
• My Website: https://www.worksbysolo.com
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