More thoughts on resin warping & shrinkage

Andy Carlson

CJ's response reminded me of some thin HO castings I poured a few years ago. I had done patterns for some Canadian 52' Z-bar steel gondolas, both 3'6 IH and 4'0 IH with help from John Riddel. I wanted very thin gondola sides, for the gondolas are open cars, and I wanted the as close to scale as possible look. The good folks at BJ Resins in Tustin, CA. suggested a resin for this. I made the patterns for the sides out of .010 styrene, exclusive of the Z-bars. I cast the sides with the suggested resin and was quite surprised at the warp-resistance the cast parts had. I had lost a gondola side casting in my car between the seats where it took over 6 months for us to be reacquainted. Through Hot summer days where the car was parked in direct sun, the surviving part was rifle-straight after this ordeal.
It is important to have a good resin matched to the specific conditions of the pour. In production work, this becomes problematic, but in my part time amateur status I was able to experiment a lot. I have some of these completed gondolas and years later they are still straight sided. I was not happy, though, with the resin for consideration of being my regular casting resin in that it was opaque in the liquid state, and was therefore much more difficult in chasing out trapped air bubbles.
-Andy Carlson
Ojai CA

cj riley <cjriley42@...> wrote: Be careful about generalizing on resin color. I was in the casting business for
many years and used several suppliers as I came up to speed. Alumilite is not
the only yellow (buff?) resin. And , as I am sure Tom and the other
professional casters know. there are hundreds, if not thousands of varieties of
resins in many colors. They are all formulated to have specific properties so
as to meet the needs of a range of customers. I didn't cast thin parts so I can
offer little to that discussion.

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