To comment on your last post, you are neglecting the force you have to apply to the ski to get the correct contact pressure on the base of the ski. From what I have seen in shops, that force could be as much as 50 lbs. That would give you way too much deflection. I would peg your deflection tolerance (I means this as the required flatness of the finished ski base) at +/- .003" or approximately +/- 0.1mm. Most modern machines probably produce more like +/-0.02mm.
I think you should also ask yourself what needs to be done to a ski when having a grind. (although it depends on if this is a school project for a grade or a real thing) What I mean by that is for the ski performance, the bottom edges of the ski are critical and that is biggest reason why you grind a ski. The ptex has an effect, but nothing like the base bevel of the ski. I have a hand tool by SkiVisions that holds a rough ceramic stone and I use that to flatten the ptex. It works pretty quickly and I paid $60 for it and the stones. Just flattening the ptex is less than half the job. I pay to have my skis ground to get the base edge reset flat with the ptex and then have a bevel of 1 degree applied consistently along the length of the ski.
The really hard part is getting the ptex and base edge removed precisely to make both flat again. If you have to cut both metal edges and a flat ptex base at the same time (which is needed in a grind to 0 base bevel) that is very hard to do with hand tools (like files or Skivisions tools). Cutting the full base width of Ptex and the metal edges takes a lot of force and clogs a file very quickly. I have a Panzar file to do that and it is not an easy or precise task. If your skis are concave (base low) it is easy to file down your edges to match your Ptex. This is what most people do who say it is easy to file a ski flat are doing. I agree in that case. If your ptex is convex (ptex high) the SkiVisions tool works reasonably well. If your ptex is flat and your edges have a 2-3 degree bevel, both the ptex and the edges have to come down (preferrably by the exact same amount) until the base bevel is 0. Then you rebevel your edges to 1 degree, and your skis are restored to proper performance.
Then there is ptex structure, but that is mostly important for racers and I will leave that topic alone.
BTW, I am a degreed working mechanical engineer, and I agree with the comment this is quite a project you are undertaking.