By Alden Hart
The “LED Light Brick” project in MAKE, Volume 18 has generated lots of good feedback for us, so we went back and asked Alden to explore a few variations on the theme of the brick casting itself, how you might be creative with it. This article is the result. Be sure to check out the original piece in MAKE, Volume 18, and also the on-line supplement containing specific casting instructions. –SMR
From the pages of MAKE
Some Experiments in Mold Making
A lot of the fun of the Light Brick is trying out different molds. Some very different effects can be achieved depending on the mold you make. This post explores some mold making options and experiments.
Smooth Surface Finishes
It can be very difficult to achieve a mirror smooth finish like the lucite “tombstone” sales awards you may have seen, as they use a process that involves different plastic, cured under high heat and pressure (about 450 degrees F and 6 atm), and which requires grinding and polishing to achieve the surface finish. Here’s an example of a failed attempt to achieve a mirror-smooth finish:
Note the mold pull-away lines by the power connector. With more careful curing it’s possible to avoid this problem, but the surface is never as smooth as a ground and polished surface. There are other problems with a smooth finish. For instance, any surface imperfections are immediately evident. If the casting is not fully cured when removed from the mold, as is common, any dust that settles on the surface will cause cratering. Over time the surface will pick up a patina. There are surface coats that can prevent this, but they tend to cloud the surface slightly.
Of course, you can always just make a casting on top of a piece of glass.
It’s perfect, but, in my opinion, a smooth finish creates less interesting lighting patterns than a textured surface.
Instead of orienting the casting horizontally, turn it upright on its end like so:
This mold was made by painting the glass master with brush-on latex mold compound. It took a while to dry, and it was hard to get the master out when it was done. But this configuration allows the circuit board to be positioned in the resin vertically, suspended by the power connector. This allows the casting to be done in one pour, which minimizes air bubbles.
Machinable wax is a very hard wax that’s actually hard enough to be worked in a milling machine. See, for instance, Grizzly Industrial’s H9042 Machinable Wax Block. It’s normally used for teaching students how to use machine tools without buying expensive metal stock. The wax can be cut, milled, carved, filed, planed, or otherwise worked, making it very versatile for shape and texture. Once you are done it can be melted down and re-used.
Here’s a life mask that I cast from machinable wax. The original mask was made using alginate directly on the model’s face, then that was filled with wax.
The nose was sculpted to restore the nostrils, then the wax master was used to make an RTV mold.
Finally, acrylic castings were taken as usual.
Once you get the basic technique down, you can make some really interesting bricks. Have fun!
Bio: Alden Hart is CTO of Ten Mile Square Technologies, a technology consulting firm that develops systems for media and communications, from the metadata to the metal. In his spare time he combines microcontrollers, LEDs, mechanics, and other small parts in ways that have no practical application.