April May 2015

S Scale Magazine

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The S Scale Resource April / May 2015 10 By Glenn Guerra Jim Kindraka and I have been doing some modeling together lately. Jim had some resin kits, and brought them over so we could work on them. As we were working, we started talking about resin kits and how they are made. I have a little experience with making them and was explaining some of it to Jim. We thought it might be of interest to other modelers, and it might help them putting their models together. First a little history because I like the history of things. Some of the first resin casting I am aware of takes place in the late 1940's. At that time, polyester resin and fiberglass cloth were used to make things. You are all familiar with fiberglass items such as boats. Most of these products were, and are made, in molds that are also made of the same material. These molds are rigid and the parts that come out of them need to have some draft on them to release from the mold. Soon there were other formulas of the polyester resin developed for solid casting. When you add the catalyst to polyester resin, the resulting chemical reaction can generate a lot of heat. If the part you are making has a lot of mass, then the heat will not dissipate fast and the part will get too hot and even burn. When you are making a boat or truck top, there is enough surface area to dissipate the heat and the part will not over heat. This is why special resins were developed for casting larger objects. This lead to casting clear blocks with things in them for desk ornaments. One of the first people offering these products to the hobbyist was the Castolite Corporation. The Castolite Corporation was sold to John Kunzie, who was John's Lab, and selling ballast to the model train people in the 1960's. John started to work with the resin adding colors and fillers to it. The polyester resin has a high shrink ratio that is not consistent, making it undesirable for masking a lot of parts that needed to fit together. The fillers did not shrink, and since less resin was used, there was less shrinkage. The next big improvement was RTV rubber. Now you could make a flexible mold that you could cast polyester resin in. John sold powdered metal fillers that were added to the polyester resin, and parts were cast in the RTV molds. The result was impressive. John cast builder's plates for the steam locomotives at the Illinois Railway museum using polyester resin and powdered brass. When you polished the casting with fine steel wool, it looked just like a cast bronze original. I might add here that John was not developing these products, but was introducing the hobbyist to them and making them available to the hobbyist. The money for development of these products came from industry. These filled resins were being used in foundries, for example, to replace wood patterns. At the same time John was doing this in Woodstock, Illinois, Bill Clouser was using these materials in St. Louis, Missouri. Bill was a commercial model builder, and these materials were a help to him. In the late 1960's, Bill produced some O Scale models made in RTV molds using epoxy resin. At the same time, John was helping American Models in Crystal Lake, Illinois make some O Scale Passenger cars with powdered aluminum filled polyester. The next improvements were silicone rubber molds and the urethane casting resins that we are familiar with today. The attractions that hobbyists and manufacturers have to this type of casting are the low up front tooling cost and the ability to cast parts that have no draft and even some under cuts. When talking about some of the history of resin kits, you need to mention Al Westerfield. Al was very prolific in the number of kits he produced and the quality of them. He brought the resin kit to the hobby as a viable alternative to mass produced models. Resin Kits

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