The press surface is what holds the parts together. There are two parts, top and bottom, that will be under nearly identical stresses. On the other hand, the bottom one needs to have either the same or less flex as the top. This is because the shape of the ski is defined by the mould, and that part rests directly on the bottom. The top presses on the ski via the air bladder, so if it deforms a bit more, that is not a big issue. Either way we have to make both of these very stiff.
I rendering of the ski press with supports and base in the corner of my workshop. Dark and light blue are the alternating layers of dimensional lumber and plywood.
The design that I am using as a, very rough, guide, used laminated 2 X 12 lumber and plywood. I don't know what the dimensions of the plywood or the width of the surface is, but I do know what I want. Right now I'm going for 300mm wide opening, and that needs a lot of boards. I just don't know how many, or which combination is best. A quick trip to Google docs and I was able to whip together a spreadsheet that helped out. Plug in the width of the opening, and it will calculate the values I want to know for different thicknesses of plywood.
What values do I want? I want to know how much it will intrude into the support beam, and how close the edge of the support beam will be to the center of a piece of non-plywood(closer is better). With the current values I think that a platform 341mm wide(only 300 usable) consisting of 7 pieces of 2 X 12 X 10' lumber with 6 pieces of 1/2" plywood would be best. Interestingly, if I drop about an inch on the opening width and use 270mm, suddenly 5/8" plywood becomes the best option. I've not locked down the opening dimension yet, still designing it, and so I made sure that I could easily recalculate if needed, but for now I will go with these figures.
A quick trip to the CAD software and we have an updated drawing. I setup 8 of the 8 X 8 beams to be the full height of the garage, but I don't expect to need that. I will probably bring them down to just above the press top once ready, and may remove some of the side ones and replace them with 8 X 8 support feet. Also the height off the ground of the platform is arbitrary at this time, and will probably be changed to match the height of my main workbench when it is not resting on it's wheels.