We are starting a project to build ourself an 18 inch Dobson. We have bought a mirror from Galaxy and cell + spider from Novak ( the cell is a traditional 18 point floatation cell).
We would like to make a serrurier-truss type system from which we can later use the optical "tube" assembly to put in a permanent splitring or fork. That way we can use the scope for photography while still maintaining the possibility to use it as a Dobson if we want to.
I have a pile of issues of ATM, but before we start working on the scope, I would like to get feedback from the atm mail list on "do" and "don't" for this (big) scope.
We have experience building a dobson ( 8 inch full tube and 12 inch serrurier-truss ).
However, I always have the impression that our scopes are build *too* heavy.
Questions that arise now :
1) What thickness of plywood to use for the primary mirror box and rocker box
2) What thickness of aluminium tubing to use for the serrurier truss tubes
3) What thickness to use for the ground board
4) What thickness to use for the semi-circles that will be used as altitude axis
5) We would like to make the secondary mirror cage rotatable ( for later ). Are teflon pads between two rings of plywood ( one covered with formica ) enough to provide a smooth rotation of the cage ?
6) Anyone used the TECH2000 motors on a dobson mount ? What should we provide to mount them, and are they easy to use in practice on a Dobson ?
Thanks for any feedback,
Dominique Dierick