> It is my understanding that If you make your mount parts out of aluminum
> instead of steel, they will be about 3 times more elastic. So you have
> to make them thicker to get the same stiffness, and you end up not
> really gaining any weight advantage for the same strength.
> A hollow steel tube the same weight and diameter as a solid aluminum
> shaft is probably stiffer.
Take a good lok at two part article in S&T about mechanical analysis of telescope/mount design (I think it was sometimes in maybe 90-91 ?). The most important thing to remember is that stiffness is proportional to the FOURTH (!) degree of diamater. So you don't have to use 3 times heavier aluminium tubes to get the same stiffness. In fact, a 2 inch aluminium tube will be a much better choice for the shaft than 1 inch solid steel. Another thing to remember is that hollow tube looses very little in stiffness compared to the solid shaft. There is really no reason to use massive solid shafts, except if you want your mount to be heavy !
Bratislav