I've been looking into building skis for this coming season so I have been browsing the skibuilders.net forums. Tons of good information available there. There are a lot of people who built their own presses, the basic idea is pretty simple, but the costs really add up in the steel and welding. I was surprised to learn that the presses are pneumatic, not hydraulic, so they inflate a tube or tubes to like 70psi in between a steel frame and wooden mold and it just presses the shit out of the ski materials. The harder you press the lighter the ski? I'm not sure because I just started looking into it, but I think it's because you squeeze more epoxy out.
There are also cloth presses which seem interesting to me, because you don't have to buy tons of steel and have welding experience, but you can still press a pair of skis with a good amount of psi. The guys on the forum said that vacuum bagging produces an equivalent force of like 4 psi or something, I'm not sure though so don't quote me. You can get these cloth presses up to like 40 psi which is pretty solid.
Vacuum bagging is definitely the most accessible for most people, and it can definitely make a satisfactory pair of skis. Plus if you get into vacuum bagging you can make skateboards and stuff pretty easily with the same equipment. I am not sure it is so easy with the big frame-style presses.
Idk why it matters a lot that there are previous threads, just kinda seems like a cool thing for the NS community to talk about. I stumbled onto iggyskier's thread, which I am pretty sure is Scott, the founder of ON3P, on TGR forums from like 2004 where he was designing and building his press and pitching his idea for ON3P skis. Kind of a cool bit of ski history especially since NS enshrines ON3P.