Well, The rivets seemed a good idea at the time but a year on and experience has taught me that the center support of a “pseudo” Serrurier truss has to be rock solid. There was a small visible movement in mine as the rivets were not solid enough and that plays havoc with the collimation so it was time for a “Rolf special”. A local machine shop cut and welded two aluminium octagons together for the center support which is now rock solid. The plywood main mirror holder had been butchered a bit over time so was replaced with an chopped down aluminium job. Can't remember who made it but I had it lying around so in it went. Decided it was time to fix the secondary screws. Every time I moved a screw to collimate the secondary would rotate. Found an old post on cloudy nights that suggested using axle cap nuts with a hole drilled through them for the screw to push against and it works well. No more rotation. You will find the “Improving Secondary Collimation Adjustment “ blog in the archive section of cloudy nights.
So children, the next time you build a truss scope make sure the center support is built absolutely rock solid.
Cheers
Stephen
Original design
http://www.iceinspace.com.au/forum/s...d.php?t=107896