At AfritLabs we are dedicated to improve upon and develop further our primary device, the IcosaLEDron. When introduced last month, this geometric LED array was protected by a flexible 3D printed NinjaFlex material. It works well and looks great, but printed unreliable and timely. A different material could be more efficient and just as durable, therefore the protective rubber shell is now a tough translucent silicone.
We discuss briefly our method of making molds and casting parts derived from 3D printed objects in this IcosaLEDron Impovement.
A Master model was designed and 3D printed with the mold in mind. A border was designed to aid in the casting process, and the grove between domed faces was chamfered to improve coverage and eliminate bubbles. This is the piece that the mold will be made from. Step by step instructions for prepping, measuring, mixing, and pouring molds and casts are found all over the web and YouTube. Included here are a few tips to keep in mind.
Since we are using a platinum catalyst type silicone for the final pieces, the mold needs to be of platinum cure silicone too. We used Mold Star 30 from Smooth-On and experienced positive, bubble free results without any vacuum degassing.
The Specific Gravity of the material is needed to determine how much to mix. This is in the products’ Technical Bulletin, a must read before using any pourable silicone. Considering half an inch from the objects surface a CAD model of the proposed mold was created, and using Netfabb to determine the volume, calculations were made to find how much of part A and B to mix. This helps reduce any waste of materials.
Our mold box was made of glossy white foam core for walls and seams filled with oil based clay, nestled in an appropriately sized SparkFun box. Follow the directions, wear gloves, and use a mold release if you choose to experiment with mold making. It’s relatively easy and yields impressive results.
CASTING HYBRID PARTS
Silicone proved difficult to glue anything to, so we had to rethink how to attach the rubber outer. This resulted in the addition of ribs inside the negative space of each triangular face. When the IcosaLEDron net is placed into the uncured silicone, the liquid rubber flows over these ribs and when cured will incorporate both parts permanently.
Print Files available on Thingiverse.
We decided to cast our part in SORTA-Clear 37 Translucent Silicone Rubber. This was based on it having a high tear strength and robust Shore 37A hardness, 1:1 mix ratio, and a short 4 hour demold time. Being food safe is a bonus, although it collects debris easily so we don’t recommend testing that. Smooth-On describes this product for making molds rather than final objects, but it works great for casting durable translucent rubber parts.
It is helpful to glue in and wire up the LEDs before casting. Previously the square LED holes were blocked with scotch tape.
After some trimming of excess material along the edges of the newly cast part, and the normal assembly, an IcosaLEDron clad in durable silicone emerges, bouncier and brighter than ever.
Kits for sale Q1 2015