I had a great little side project / challenge this past week helping my friends and local purveyors of coffee, cycling lore, and good craic down at Grupetto. Since I work almost entirely on medical stuff it's fun to be able to help some local people out and do something a little bit different from guts, patent searches and, more recently, writing journal articles.
Krys has an old Gardin bicycle missing one very specific head tube badge, that little manufacturers plate on the front of the bike. Gardin was a Canadian manufacturer that went out of business a bunch of years ago, so finding a replacement badge may not be so easy. He had borrowed an original for reference and wanted to see if I could use my fancy schmancy computer and CAD skills to first 3D scan it, then fire up the 3D printer and print it, then paint it to match to copper. The original badges were pewter electroplated with copper, so having looked at it briefly I went away and thought about it, as I do with most things. Fortunately, I had a little longer to think about it than anticipated. Krys temporarily misplaced the badge beneath the counter at the shop, giving me some extra time to experiment by casting a few coins. No pixels or pricey 3D printing resin would be consumed in the reproduction, I told him, we'll just "cold cast" this.
Cold casting is a means of producing metal looking parts using resin and fine metal powders. They're actually relatively dense and conductive, just like the actual metal, but they don't quite feel the same since they're a composite. They're a little too light, they don't have that metallic feel or "tang" when you hit them, but they look almost spot on. Since I already had the resin, I took a little trip to Royal Meats BBQ (ahem, Sculpture Supply Canada) in Etobicoke last week. Both Royal Meats and SSC are inspiring places; I had an enormous hamburger at the former, then waddled into SSC where I picked up some powdered copper and some heat resistant silicone. That way, if the cold casting didn't quite work out we could make a second, more traditional poured mold and take it to a local jewelry maker and have her cast it with pewter.
Though you do have to think about them in weird ways as they're kind of an exercise in thinking about negative space, making molds is relatively east. But I'm totally new to cold casting. Having fiddled about with some success on some Czech coins, I figured I was good to go. Buying a coffee last week and feeling ready to try this, I suggesting Krys look on the floor underneath the counter, which is exactly where he found the missing badge. I took the piece home and promptly made a simple two-part mold that would be kind of like a crude coin press. Pour the resin/metal mixture in, gently press the core down and the excess material would squish up out of two overflow vents at the high points of the piece. Let it cure for an hour, remove, polish it up with some steel wool, a rotary tool and some buffing compound. Should work without having to do any fancy/crude injection molding.
Et voila, it worked! Success!
Now maybe I'll do some aluminum or copper anatomical models. Iron heart here I come!