Resin casting in a two part mold
Last week’s post showed how I went about making a two part mold for a dinosaur plastic toy. While the mold was made with the dinosaur on its side, the idea was to pour resin into the mold while the dinosaur is vertical. You can see what I mean by the picture at left. (And pay attention to those undercuts. You will see why those are important in a minute.)
Before pouring the resin, I made sure to bring both parts of the mold together with masking tape. I then set it upright in a plastic cup.
I mixed 15 cc total of the Resin Obsession super clear resin and added in a bit of the Alumilite green pigment. Because the sprue hole was small, I used a toothpick to help guide the resin into the mold. I poured in some resin, then rocked the mold back and forth, trying to get bubbles to release to the top of the sprue. I filled resin halfway up the sprue before allowing it to cure.
This is what my resin dinosaur looked like 24 hours later. (Perhaps you already notice the two problems with the casting.)
Once the resin cured, I was able to peel open the mold and remove the dinosaur.
Comparing the casting to the original, you can see where my green dinosaur didn’t fare so well.
Problem 1: The arms and toes on the feet didn’t fill with resin. This was a problem that I was expecting. As shown in the picture above, I needed the resin to go down, then up. Because of surface tension, resin (amongst other things) does not want to do that.
Problem 2: The head didn’t fill. As I was pouring the resin, I didn’t want to have too much extra to sand off from the sprue. Even though the filled the resin into the sprue, I didn’t fill it all the way to the top. I didn’t account for bubbles rising to the surface of the sprue, allowing for more resin to fill in.
Overall, I ended up with a zombie dinosaur: headless and missing a few limbs.
On a side note, flashing is something I talked about before. It’s where resin leaks out between the two layers of the mold. It occurs commonly with two part molds, but can clean up nicely.
This view of the underside shows the resin casting voids.
The body turned out well. I like that the Composimold did a great job of picking up the ‘scaly skin’ detail on the original model. It transferred to the casting.
The good news is that the back half of the dinosaur (cast as the bottom half of the mold) did pretty well. The tail casted fully and with a lot of detail. The toes on the back feet weren’t complete for the same reasons the arms weren’t complete but not nearly as bad.
So what’s next?
I think I’m going to try casting the dinosaur as a top half and bottom half. Maybe then the arms and legs will fill up completely.