Hi Indeed it looks a good way. So if I pick a fish scale and took all the z axis all together : i will have 70 lbs. But if I put over the carriage, the preload and friction of those will eat some of the weight, So i might get a value of around 55lbs . I think it might give a usefull value as well ? or it's really with the ballrod in place too ?
http://www.nookindustries.com/Conten...eGallery_5.png
i did get this calculation for the screw.

But as James said: the spring approach is quite interesting. An oleo might be ok too, but not too big at same time, i'm not sure where to get it. A spring could get some decent ''weight removal.''