RESIN CASTING

HOW IT STARTED

I started playing with resin while developing the UFOS model¬†by borrowing this technique from the production of the so-called “river tables“, in which the resin is poured into the natural cracks and fissures of the wood, or between the live edges of two different boards.

I modified the method by milling pockets to accommodate the resin, but above all by studying a double casting system, for the management of 2 colors: the central colored part and the black details (they are cast resin too).

UFOS Ukuleles From Outer Space

For the application of this system I had to use some tricks learned by studying the technique of silicone molds, with which I can separate the phase of the black casting from that of the colored casting.

Timing is of fundamental importance in this process. The two-component resin, once mixed, has a certain pot-life (which unfortunately also depends on the temperature: my summer UFOS construction method is different from the winter one ūüôā ) that will greatly affect the choices to be made to increase the quality of the final result.

The swirls you see in the resin are created, more or less randomly, by hand using a toothpick. The exact moment in which to trace these signs is the result of experience, as it depends on the pot-life and its variables. Tracing them too early would be useless: the resin would still have enough time to re-homogenize and make them invisible. Tracing them too late on the other hand, thus acting on a too viscous resin, would cause air to be incorporated without being able to rely on the liquid’s air-release property. The result would therefore risk being ruined by bubbles or voids.

THE WOOD GRAIN PROBLEM

The choice to use local hardwood has complicated things a bit: their fiber absorbs a lot of resin, much more than the mahogany I once used, which risks leaving colored spots and streaks.

The first solution I tried was to seal the grain of the channels and pockets with a synthetic grain-filler. Unfortunately the narrow geometry of the channels (especially of the black resin ones) made it very difficult to clean up the residues of grain-filler which therefore left lumps here and there on the side of the channels, going to ruin the final effect.
A second attempt was to try to make the resin more viscous, so that it would struggle to get into the grain of the wood. To do this I used Amorphous Colloidal Silica, an inert filler capable of making the resin similar to a thick mayonnaise. The solution seemed to have worked, but there was a predictable problem: the resin, no longer liquid, has lost its air-release property and therefore, once cured, it has proved to be full of bubbles. Another attempt failed.

UFOS ukuleles building

The right solution in this case (as in many others) came from tradition… Shellac! TADAAN

With 3 coats of shellac, each with a different solution, it was possible for me to effectively seal the sides of the channels, thus making the wood grain impermeable to the resin, without leaving around residues that could compromise the final result.
Even if some shellac lumps would remain, it would be easy to remove them (both before and after casting the resin) because shellac can be easily dissolved in alcohol.

The whole process described up to here would have been possible even with a normal epoxy resin.
Following the principles on which I decided to base my business, however, I chose to use a bio-based resin. These kind of resins tend to be more expensive and difficult to find, and sometimes they give some more problems in the management of atmospheric variables, but if we all used them instead of conventional resins there would be an important improvement in terms of carbon footprint.
I personally use and recommend Supersap resin, by the brand Entropy Resins. You can read some more info about it on my materials page.

UFOS Ukuleles From Outer Space

WHAT'S NEXT?

I’m glad I learnt this technique. I started by simply applying it to solidbody instruments: the easiest to build (and the easiest to say goodbye to, in case of tragically failed experiments). Now the next step is to apply it also to acoustic instruments, in the specific to bindings and rosettes.
Here you can see a first experiment on a binding (still done on an Elettrico).

DANG-O-METER

The Dang-o-meter is  a scientific instrument capable of quantifying the amount of annoyance, screams, anger that has come up during a particular innovation. I use it to give an analog value to the degree of difficulty to the various experiments that you find in the Research and Development section.

The result in this case is:

MODERATELY MESSY.

Thanks for reading and see you to the next experiment!
Marco

gauge_3
Leave a Reply

Your email address will not be published. Required fields are marked *