molding and casting

This week, I used the 3-axis CNC milling machine Roland click here for the machine to mill an object (variant 1), which I later cast in silicone to create a cake mold for pastry. I was inspired by a video from a pastry chef and was eager to try it out myself . Whether it was a good decision, you will find out soon.

To make a better comparison between a CNC-milled object and a 3D printed object (variant 2), I tested both methods. This allowed me to better understand the differences in processing and results.

For the project, I used the following materials:

Materials for the Project

I’m excited to see how the final result turns out! Stay tuned to see how the CNC-milled form compares to the 3D-printed one.

material Silicone

TFC Silicone Rubber Type 1 – Technical Properties click here for the TFC Silicone

Shore Hardness: A 18–20

Viscosity: 3200 mPa·s

Mixing Ratio: 1:1

Short-Term Heat Resistance: up to 150 °C

Working Time at 23 °C: 12 minutes

Curing Time at 23 °C: 60 minutes

Tensile Strength: 3.1 ± 0.2 N/mm²

Elongation at Break: 430 ± 15 %

Tear Strength: 6.5 ± 0.5 N/mm

Dimensional Change: 0.01 % after 24 hours

CNC processing

I tested two materials: one is Styrodur and the other is MDF. I tested the CNC machine with a small coffee bean and with an apple core model that I created in Fusion 360.

For the milling process, it is important that the material block is no larger than 60 x 60 mm in height and thickness. The UI of the Roland CNC machine is quite simpler compared to other CNC machines.

It’s important to build some support blocks, and the supports should not alter your object too much.

Here you can see my steps:

This is the setting for the support.

Here you can see the setting for the surface finishing

Here is the setting for the material.

The process took quite a long time (more than one hour), and at the end, I had to cut the supports off the object and sand down the connection points.

After that, I had to do quite a lot of post-processing on the MDF coffee bean using a chisel and a hammer until I reached a somewhat satisfying result. The milling bits we have are too big to fit into the small grooves of the bean, so they simply left parts uncut.

For the Styrodur model, I couldn’t do much post-processing, but luckily, I didn’t really need to.

Afterwards, I coated both models with rapeseed oil to prevent the silicone from sticking during the casting process.
Instead of using the usual silicone spray, I used rapeseed oil because I was working with food-related items and wanted to keep the process as food-safe as possible.

It was important to me that the container I used for the silicone was a recycled plastic box, so I wouldn’t waste too much material. Therefore, I reused an old german potato salad box and an empty smoothie bottle.

For the material I used some Kautschuk material how is Food safe and is bubble free you can find here

When preparing for casting, it is important to ensure that the object has at least 1 cm of space around it within the mold. The bottom should also have at least 1 cm clearance to prevent holes from forming. Additionally, when mixing the material, it must be combined at a 1:1 ratio. Initially, I made the mistake of trying to weigh the components using a scale, but unfortunately, the scale turned off mid-process. Therefore, using measuring cups with precise volume markings is highly recommended.

It is also important to pour the material slowly and from only one spot to minimize the formation of air bubbles. When stirring, always move in a figure-eight motion to avoid trapping air. During the pouring process, continue pouring into one single spot and carefully watch for any bubbles. I also tapped the mold gently from time to time to help release any bubbles trapped deeper inside.

• Working Time at 23 °C: 12 minutes, Curing Time at 23 °C: 60 minutes

Here you can see the broken Styrodur object. The MDF material is more durable and did not break when I removed it.

I then used the molds for casting. One was filled with water to create an ice cube, and the coffee bean mold was filled with coffee for a coffee cocktail. Additionally, I experimented with making pâtisserie-style tartlets.

It wasn’t easy to remove the cakes from the molds. The cream filling was too soft for this method. The molds work well for ice cubes, but not for cakes — or I might need to find a different recipe.

Here are the links for the cake:

click here for the cream

click here for the fruit gelee

click here for the biscuit

FDM Printing process

For the FDM printing process, I created a model in Fusion that was designed to resemble a small tart. I 3D-printed it using very fine layer settings and minimized the infill to just 2% in order to save material, as the object would be discarded afterward.

After printing, I coated the object with four layers of primer, allowing each layer to dry for 20 minutes.

After the first layer, I also applied filler to cover some holes caused by a printing error — the filament spool had developed a knot near the end.

Once everything was dry, I sanded the surface using 260-grit sandpaper, wearing an FFP4 mask for safety.

Next, I blew off the dust with compressed air and lightly coated the model with rapeseed oil. From there, I followed the same process as with the CNC-milled objects.

In the end, I attempted to create a cake using the mold, similar to the previous trials.

Unfortunately, even after chilling it overnight and briefly placing it in the freezer, I couldn’t remove the cake cleanly from the mold.

I’ll spare you the pictures this time! I will try to use the mold for making an ice cube instead.

One thing I can definitely say: molds with such tall shapes are not ideal for casting objects that need to be cleanly removed afterward.

CNC vs. FDM finsih

Through this project, I learned that CNC-milled molds, especially from durable materials like MDF, offer more stability and smoother results for casting compared to delicate Styrodur or fragile 3D-printed parts.

While 3D printing allows for more complex shapes and faster prototyping, it often requires extensive post-processing and is less reliable for clean mold removal, particularly with tall or intricate forms.

Overall, CNC milling provides higher-quality surfaces with less risk of failure, but it is more time-consuming and limited in detail compared to the flexibility of FDM printing.

Group page

If you would like to learn more about the materials we used and take a closer look at the datasheets, please visit our group page:

click here for the group website

stl-files

click here for the apple file

click here for the bean file

click here for the cakepart file