sand casting: using a 3d print as a pattern for casting in metal

I know I've posted this before, but I needed to make some more wing nuts so I decided to use my 3D printed wing nut from McMaster Carr (downloaded from their site since they offer some hardware 3D models for free). I shot more photos that explain the process a bit better, so I thought I would post these so people could understand how it's done. I'm using some homemade flasks that I made on my South Bend lathe, but I've shown my commercial cast iron cope and drag flask. My flask just has a small lip that fits inside the other half so they fit together nicely. I have created an indexing mark as well so I can make sure the two halves are aligned when I take my pattern out and put the flasks back together. These could be built out of almost anything though. For more on the process I recommend Dave Gingery's book on the Charcoal Foundry. I'm using delft clay/sand from Rio Grande. You could also use Petrobond and some people make this themselves. The rest of the images should be rather self explanatory. My only advice is make sure to separate the charred sand from the good sand after you pull your finished cast piece out of the mold. Throw the charred stuff out as it will ruin your sand if you mix it in with the good sand.