Sunday, April 4, 2010


Making valves -  Seeing the need for many more gate valves in the 3/8" to 1/2" sizes to finish the by-products plant I turned to resin casting as noted in a previous post.  

I am by no means an expert on casting techniques and everything continues to be a learning experience for me.  I most cases I try to use one part molds - they are easy to make and easy to fill and get good results.  You will note, many commercial car kit makers also try to use one part molds.  

For the valve bodies I opted to cast everything, including the operating mechanisms and stands for these mechanisms as one casting.  We will still need to add a brass operating rod and a sheave from a Tichy sprue.  After multiple failures I am on track and producing valves as I find time to get down to the basement, empty the molds and fill them with new resin.   These castings are not perfect - they have some air bubbles here and there to fill, but I am generally pleased with the results.  

Here are some tips:

  • When building the master and setting up the mold, make sure you build in plenty of channels to release air and prevent bubbling, and also orient the main fill sprue to hook around and enter the mold from the bottom.  I learned this from an older Fine Scale Modeling article - it helps maximize the vertical pressure on the resin and thus push it into the crevices of the mold better.  
  • Avoid small pours if possible - when I started with just one valve, I was mixing 1/2 teaspoon of each part of the resin and still had a lot of extra.  In quantities this small, one drop here or there too much and the resin will not cure right.  If you look at some of the defective valves to the far right and also one or two of the good ones, the color is yellower.  To avoid this I pour multiple molds at once - in the picture I am pouring the 3/8 valve, the 1/2" valve, and the narrow gauge ingot car.  For overflow I have a flat mold with access hatches that I use.  These four molds use 2 teaspoons each of both parts of the resin, an amount that is better for consistency, but still not that much liquid in the scheme of things.   

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