You need 4 pieces of plywood. The rough sizes are below, but you should choose them according to the juice tray you already made. The thickness of plywood should be about 40mm. Thicker is better. To thin and it will just break. I did some FEA analysis, and it came to about 38mm, but this value is only a rough guide.



2x plates for the top and bottom. (300mm x 300mm x about 40mm)

1x plate for the tray holder. (220mm x 220mm x 220mm x about 40mm)

1x block for the plunger that does into the metal tray. (160mm x160mm x about 40mm) This depends on your tray dimensions.

The good thing is that precision is not important!