Well I've got a delivery date for the mirror so will share some of my thinking for discussion. Previous discussion on scope size here: https://www.cloudyni...4-16-f4-or-f45/
Basically I'd like a bigger scope but have a small house, and it needs to be portable. My existing main scope (link in sig) is a lightweight 10" hexapod. I'm very happy with the performance and portability, but it is only balanced with eyepieces up to ~350gm. So, along with a step up in light grasp and resolution, I want this scope to be able to handle heavy eyepieces/ binoviewer plus coma corrector. I'd like the option of a finder scope too.
So, for starters here's the mirror support plot from PLOP-lite via CBScope:
Looks like a six-point cell will be more than sufficient (this is based on modelling the full-thickness in quartz as per https://www.cloudyni...ject/?p=4825659). Intending a triangle of steel tube to support, with the ends connected direct to the six-leg truss. The rest of the LTA will be laminated from birch ply similar to my 10", likewise rocker box and ground board but need to draw proper plans up.
Edge support - not sure here. With the Hubble Mirror being a sandwich, some extra complexity is involved. I think I'll try two-points at 90 deg, with short vertical whiffletrees to share the load to both plates. But a ladder sling is the other obvious option.
UTA - Merope's looks like a good starting point - two rings of 9mm ply, ~50mm wide. Moonlite focuser, on a 12mm board. Other bits of ply or tube to join, 2mm ply to line. Inner diameter mirror + 44mm.
Secondary - played a lot with NEWT and Mel's calculator. Choices from Hubble were 70mm or 80mm but I'm probably going for a 75mm from Orion UK which gives 11.8mm field at 100% and 45mm for the 75% - which should cover any field stop I'm likely to use. At this position the paracorr will impinge on the light path a little, but only at the biggest field.
Spider - not sure. Brass sheet offset like my 10" seems simplest, but maybe wire? Not built a secondary support before so need to think about that too.
Truss - again I'll be using female steel rod ends at the bottom and male igus at the top, all M8. UTA fixing will probably be the same with eyebolt and thumb nut, LTA I've got some ideas - my current fixing works well but is awkward to access with the bearings on.
Just pricing up carbon tubing - looks to be about £120 vs £30 for aluminium + heatshrink. Inclined to go for carbon as it's a nicer finish, warmer to touch and I can create slightly tapered tubes by nesting smaller sections at the ends. That will also allow the tube lengths to be finely tuned rather than having along length of threaded rod, and might even be a bit stiffer than Al.
Any input welcome.