I have a brilliant creative director, Chris Howes, who sent me an e-mail the other day. I have shared part of it below so you can get an idea of what we are dealing with getting the molds made for Sam - our first Hatched in the USA duck.
Chris was working on sending the first prototype to Bob, our new mold maker in America. In fact, he is already working on our second project, a Loon for the State University of New York duck race. Below is a bit of Chris' email that I mentioned. Good news though, as I write this it has all been worked out and Bob is already in production on our first molds!
Subject: Re: update
Been a difficult process getting it to the right size in wax. Also had to take the time to machine the bottom weight recess accurately to a non standard diameter due to shrink and have now created the corresponding plug to fit (which we can use from now on). All wax work is done and I took time to build my rotocast machine because I need to provide Bob with 5 hollow urethane castings that are difficult to do by hand. There are a number of waiting periods while waiting for wax to cool, rubber layers to cure, etc. during which I have started the loon, so he's under way already rather than waiting until after Sam's all done. It's taking longer than I would have liked (it's a learning process, got to change technique to fit new process).
The upside is the worst is over! The intermediary rotocast urethane prototype I made to test weight placement floats well and "pops up" even when thrown upside down into the water. The final wax looks good and is a good size. Now I just have to get all the urethanes done and cleaned up and off to Bob. The urethane I have takes a while to cure and sets or "gels" very suddenly making an even wall thickness casting difficult to achieve. Luckily, my rubber and urethane supplier, has a special rotocasting urethane resin that cures faster, but with a slower more gradual gel time than regular resin so the wall thickness is nice and even. I've got some on order.
For the future now I have a rotocasting machine, a standard plug and a recess mold so I can make the same size recess on every duck without having to machine it every time, and a technique for finding the proper position for the weight recess. Things should be much smoother from now on. Whew!
Oh, and I had a thought on the technical design side... I put a small dimple on the inside surface of the recess (out of sight) for pressure equalization if needed. When the vinyl is cast it should be a bit thinner over the dimple. The vinyl is hot, therefore the air trapped inside is hot and expanded. If the vinyl casting is sealed and cools the air cools and contracts making the duck potentially seem under inflated. So, the air pressure needs to be equalized. The thin area of the dimple is easier to pierce allowing air in or out as needed. Then the weights are added and plug glued in sealing the duck!