> >5) Would it be a good idea to put an additional teflon pad in the middle of
> >the ground board (with the central bolt passing through it)?
>
> It would make the scope turn easier, but it will be at some sacrifice
> in stability. With the kind of central bolt bearing typically used on
> Dobs the maximum stability occurs when all of the weight is transfered
> directly though the teflon pads (as far apart as possible) to the feet
> directly below the pads - no flexing or twisting forces in the ground
> board. If the central pad takes weight it will cause the ground board
> to flex.
It will also cause the rocker box to rock -- 3 pads must inevitably lie in a plane. 4 won't -- they can, but they won't :-)
> Teflon should be loaded at 15psi/sq inch (to those in the rest of the
> world, I'm sorry about the goofy units)
Ermmm... that's goofy in _any_ system -- I think the "/sq inch" is redundant :-)
> Low friction is not really the goal in telelscope bearing design.
> The goal is to get the right kind of friction. A sticky bearing will
> overshoot when you try to nudge the scope a little bit. A properly
> designed scope has wonderful "buttery smooth" feel. Once you use a
> scope like this, you will never be satisfied anything else.
I totally endorse this. My first dob (8"mirror, 6" diam altitude trunnions) lived without any formica on these bearings -- the matt-varnished marine ply trunnions ran _perfectly_ on the teflon pads. Thar was beginner's luck -- I have never had that experience subsequently.
Clear Skies, Steve <sft@aegis1.demon.co.uk>