Molding and Casting

Up to this point in our FAB Academy journey, we’ve already learned how to bring to life (almost) any shape we desire. With 3D printing we can print any piece we can think of (that we can design). The CNC router is great for bigger products, like furniture. But what if we needed to get multiple copies of the exact same thing? A 3D printer would struggle in that regard, specially with the amount of time that would be needed for single printer to produce multiple things.

Molding and Casting is the process of creating the “stencil”, from which a defined product can be easily replicated. Once a mold is properly constructed, it can be used to produce an infinite amount of copies that will always be exactly the same. For projects that require multiple identical pieces, taking the time to think and design a mold rather than using morr “conventional” methods, like plain 3D printing, is a smart step to take.


The Plan

My girlfriend of 3 years has always wanted something, that I’ve been meaning to gift her for quite a while now. This thing being a set of spice jars in the shape of little houses, called the “Lenox Spice Village” collecition, from the Lenox ceramic and porcelain brand. My girlfriend buys her spices in my neighborhood’s market, mainly in the shape of small plastic bags. This “spice houses” will allow her to have a place to store her spices rather than using that plastic bag. Here’s the problem: I live in Mexico. Lenox only exports to the US. Getting the spice village set into Mexico would be a logistics nightmare. This goes without mentioning the price of the set is quite elevated and it is almost never in stock, as people rush to buy and resell as son as there is stock available.

Lenox Spice Village

In the spirit of “problem solving” that this FAB Academy has indulged me with, I choose to work with ceramic for this week. The idea is to create a “copy” of the spice village houses using a mold and ceramic. After talking with a local instructor about this idea, we came up with the following plan:

  1. Create a 3D model of each house, split into 2 halves.
  2. Create a plaster mold of each half piece.
  3. Join the plaster molds and pour ceramic paste into them.
  4. Remove the plaster mold and retrieve our final piece.

Note: For bigger final products it is recommended to use the CNC Router to carve out a large pre-made plaster cube. Because of my final product size (and my previous experience with the CNC Router…), the 3D printed mold was a better solution.


Step 1: 3D Model

Designing the 3D model for our house was pretty straight forward. I booted up OpenSCAD and tried to replicated 3 houses of the set with as much detail as possible. This houses where looking amazing by themselves, but I was afraid that the extruding details of some pieces wouldn’t allow me to remove the plaster mold once the ceramic had settle down.

detailed Roof Example

Something I learned during the Machine Design Week (thanks to Gerardo Mora) is the practice of going from the basics all the way to our goal. With this in mind, I simplified my design to a simple, no detail, shape of a house. This way, I can learn what works and doesn’t work in the most basic scenario posible, without having to worry about anything that can result from adding this details. In a future, once this week is over, I will add the desired detail and, using everything I’ve learned from this week, retry the process.

Luckily for me, OpenSCAD allows me to easily turn off all the detail, leaving me with the basic shapes. And with a single step, I divided my piece into two. My house is symmetrical, so this halves I was getting where enough to make the hole mold, I just needed to print them twice. The only consideration I had to make when 3D printing my mold is that, when working with ceramic, the final product tends to be ~12% smaller than the original mold. To counteract this, we just need to scale our shapes by 12% in our slicing program.

Mold Printing

This pieces turned out to be larger than I expected. Printing them on our trusty Ender S3 Pro would not only take 8 hours at a low quality (0.28mm) at 20% infill. So for this print in particular, I used or University’s Original Prusa XL printer. Operating the Prusa printer is pretty much the same as the Ender S3 Pro, I would even say it is printer as the Ender I use (the one on Rafa’s Cave) is controlled by a Raspberry Pi 5 running Octoprint. To use the Prusa XL printer, simply export the GCode from the Prusa Slicer (preferably with the USB stick that comes with the printer) , connect it to the printer and hit “print”. The Prusa XL printer is great for printing bigger things faster. Whilst the Ender S3 Pro would have taken 8+ hours to complete my pieces, the Prusa XL only took 4 hours.

Unfortunately, I made a mistake during this first mold print. For some reason, my pieces did not fit together as they should have. There was a small gap between the house base pieces that prevented it from properly closing. I couldn’t figure out how if it was a problem of how I sliced the base piece or the roof piece. I needed to re print. The Prusa XL was no longer an option as it now was being used for a larger project, so I had to print each piece in a single Ender S3 pro. The downside being that the amount of time needed to print each piece only allowed me to print a single house. For this reason, I printed a more detailed house, asuiming this would be the one mold I will be able to do in the week.