Saturday, December 22, 2012

Test Wax Castings with Pourable OOGOO

My early experiments with casting focused on OOGOO, a low-cost casting material made from cornstarch, silicone caulking and food coloring.  By adding Xylene (or in my case, lighterfluid) the putty-like consistency can be thinned to a pouring consistency.  The result is a very cheap molding fluid, with the drawback that the molds appear to shrink considerably over the course of several days.  However, since the stuff sets quite quickly and is relatively cheap, it should be no problem to let the molds set for a few hours and then immediately cast some parts.  To this end, I decided to try the process out with wax, as a kind of dry run.  The two molds (after a wax casting) are below:

The molds were still quite soft when I tried this and I didn't mix enough silicone to properly cover the parts so they deformed under their own weight a bit.  However the results were pretty decent, the white parts were the printed masters and the green were cast with candle wax.

It's evident on the smaller gear that some air bubbles were caught in the gear teeth.  I could probably improve this by brushing the part with mold material first.  If I were casting actual parts I would also add patterns for the bolt holes. 

I'm not sure that this process is all that practical for actually making useful parts mostly because the molds are not dimensionally stable for more than a day or so.  But it does help to get a feel for the process and challenges.  These parts are already miles ahead of the previous resin casting I made despite being considerably more detailed.  This leads me to believe that it's a good idea to use single-piece, open-topped molds when possible since it allows air to escape.  With resin, it should also allow me to poke about in the concavities to dislodge any trapped bubbles.


Chris Burger said...

James, i really like this blog, i am in recent posession of a Fab@Home Model 2, and i am desperately looking for someone to help me write some python, to translate gcode to the stupid format the model2 uses. interested?

James Gregson said...

Hi Chris,

Thanks for your interest in the blog. I'm afraid that I can't reasonably commit to another project; I can snatch a few hours away here and there for quick one-off builds but otherwise grad school has me extremely busy. I wouldn't want to say I would do it and then leave you hanging.

I will say that if you're willing to drown the problem in (a bit of) money, you could buy RepRap/Makerbot electronics and just rewire the thing to run on standard GCode. But you'll end up with something that is neither a fab@home nor a RepRap, so this may not be what you're looking for.

Best of luck on your project,


Pois said...

Add some corn starch, aka, corn flowr, it will cure in 2 hours!
You can find some results, and a video of me, mixing the stuff, here, mind, it seems it will never mix, but it does...