Thursday, August 26, 2010

FUN WITH FUNNEL CASTING!

So, you’re gleefully casting away. Things are going great. You’re a casting machine! And then it happens. The resin cast comes out of the mold missing the top third. What the heck! You try again. Same thing. And again, same bloody same. Maybe this is a loaded, or pre-filled mold? You didn’t think it was, but molds have a mind of their own. You try butterflying open the top at the pour hole, close it up and hope… maybe even send up a prayer or two. The cast is missing the top of the part again! Enter, FUNNEL CASTING! Sometimes, the configuration of the part results in a slow fill. The mold tops off with resin okay, but cranking up the pressure removes the air and compressed the resin and, in these instances, the result in an under-filled mold. Let’s walk through the process using my base for the Ultimate Showdown series as an example.

1: If I’m casting a part that needs to stay flat and true, I’ll create a foam core mother mold. Its important to spray the inside of the case with a good mold release before making the mold. This method works well if you have to cast up a bunch of parts. To date, I’ve probably cast thirty-some pieces.



2: When the RTV is cured, it’s a good idea to notch the top of the mold and case to orientate its placement later. Using a strong tape, the case is secured around the mold. You only need to tape the open side of the case. Start at the top, do the bottom and then the middle. Because I needed it to remain flat, I taped the top and bottom of each mold to prevent a possible bulge.


3: Using Krome Kote scraps, I made a couple of funnels. The bottom of the funnel should be just a little larger than the pour hole. And be careful not to let the tip of the funnel poke down too far to reach the actual part. Funnels done - give them a gentle twist to seat them.

4: I designed the disk part of the base to pivot in the hexagonal base. Both part of the base parts were cast in semi-clear resin. The disk was colored using an interference power so it would have depth, kind of like a semi-transparent stone. The hexagon part is mostly black, with a silver top. It was just easier, especially with the number of parts I’d have to cast, to cast it black and add the silver as a paint application.


5: Funnel in place, mold in the pressure pot, resin poured. Let the pressure casting begin!


6: When casting clear resin, its a good idea to let it fully cure before taking out of the mold. It has a tendency to go off more quickly than standard casting resin but takes longer to fully cure. De-molding the resin before its set up will often distort the part.


7: Fresh from the pot!


8-9: The finished two-part base. A clear acrylic spray brings out the opalescent quality of the disk. A spray of Dullcote on the hexagon, before the applying the silver, takes out all the sanding marks.
And there you have it. No more partially cast parts!

3 comments:

  1. Thx. I noticed that there are no air release channels in your mold. How do you avoid air being trapped in the cast??

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