Great minds must think alike. I too have that arbor press, but I ended up using a large vice with steel plates. I found that preheating the steel plates not only helps with a longer working time, but they really help with the finish of the plastic. Warm plates make the plastic much smoother on the outside. Here is my second attempt from today. This time I let the plastic get hotter (almost puddling) and it didn't have any cold shuts. These are just rough cut and sanded down to 60 grit. One thing I noticed. While this material is extremely strong, it is soft and bends easily. I'm not sure how thick to make the scales.
They won't give much (if any) tension due to flex. They will simply flex.
Attachment 322440