Top end ring width

Hello:

I am building a 17.5" truss tube telescope that will have a single top end ring. The focuser will be light, but the eyepieces won't, so the focuser board will have to be well supported. I plan on doing this by attaching the focuser board to the truss poles as well as the top end ring. Imagine a regular 8 pole truss with a top end ring. The focuser will sit just below the tips of the poles and look through the gap between the poles. This way, most of the weight of the focuser/eyepiece is carried by the poles, with the ring providing additional support. The job of the top end ring is mainly to tie the upper tips of the pairs of poles together.

My questions are: how wide must the top end ring be if it's 3/4" thick given this design and good plywood is used? I imagine it can be narrower than in a design where the focuser hangs off of the top end ring, but I have no experience with either design. Also, how does drilling light-weighting holes in the ring affect its stiffness? If I decide to use a relatively wide (2") ring, I'll be tempted to light-weight it.

Cheers
Mike Connelley

[COLOR="Purple"]Hi Mike!
If the focuser board weight is mostly supported by the truss poles, the upper ring can be pretty narrow...maybe 3/4", depending on the truss attachment needs.

I've been wrestling with a single upper ring but I'm hanging the focuser board off of the ring. I ended up going to two closely spaced rings to get the rigidity I needed. I drilled some lightening holes in my thicker ring and it didn't affect the rigidity much, if at all. Hard to tell since I went with two rings.

Post some pics of whatever you end up with!
Bill[/COLOR]