Monday, April 9, 2018

Molding Monday: Unboxing & Trimming the Mold, Pouring the Resin

So when we last left the mold-making process, I had just poured the rubber into the mold box and used a Rube Goldberg-like setup to hold everything in place (thanks DandHColonieMain for the observation). Click here to see that (and the rest of the previous steps).

Once the rubber cured (it's supposed to cure in 4 hours, but I left it overnight - well, for a bunch of days truth be told...), it was time to undo the Goldberg Press and unbox the mold:

You can see in the pic above how 1) I didn't have quite enough rubber to cover the master, and 2) how part of the master poked up as a result. This was actually a blessing in disguise since it gave me a point on which to place the weight to keep the master from floating (yes, floating) up through the rubber as it cured.

Next step is to remove the foamcore box, which is a simple matter of just peeling it away. But if a picture is worth a thousand words, how much would a video be worth?

Sorry it got cut off (phone ran out of space), but you get the idea.

Once I got the master out, this is what I was left with. Some trimming to do.

And, flipping it back over, you can see where I didn't have quite enough rubber to cover everything. I'll just put a piece of packing tape over the hole to keep resin from leaking through when I do the resin pour.

But, all in all, I'm really happy with how the mold came out - especially for my first time!

I just needed to finish trimming where the rubber had seeped under the master. Trimming was easy with a new x-acto blade - and here's how it looked when all that trimming was done.

Now for the fun part - mixing and pouring the resin. Here are the steps:

  1. Put on some rubber gloves and make sure you have a nice, level spot on which to place the mold (of course, cover the spot with plastic or - as I did - use a piece of plate glass - to keep any resin from going where you don't want it to).
  2. Gently shake the two bottles of resin - parts A & B - to mix the contents.
  3. Pour equal parts of A & B into two separate cups.
  4. Pour the two cups together into a larger, clear cup & stir gently and slowly to mix the two parts together.

Here, the resin is mixed together and the mold is standing by. I'm waiting a few minutes for bubbles to make their way to the surface. You have about 7 minutes working time from mix to pouring.

Like with the rubber for the mold, pour a long, thin stream of resin into the mold to reduce bubbles. Work from one corner to the other, filling the entire mold.

Overpour slightly so you're sure the entire mold is filled. You'll probably see some bubbles come up - I just blew on them and, when necessary, used a small brush to pop them. Next time, I may be a bit more aggressive with a toothpick.

To ensure that the back of the casting is flat, place a piece of glass or acetate on top. You can see here that it squished out the resin a bit. The last time I did this, I used plastic wrap instead of acetate - but that resulted in a very wavy back.

As a final step, I weighed down the acetate on the resin to make certain it'd lay - and stay - flat.

Now I just need to wait for it to cure. The instructions say that it should cure in 15-20 minutes (you know it's cured when it turns from clear to white), but to be certain I just plan to leave it overnight.

So far so good! I'll be interested to see how my first (well, technically, my second) casting comes out!

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