Quote:
Originally Posted by alistairsam
Hi Rolf,
Thanks for the suggestion. yours is a work of art and I still haven't ruled it out. it all depends on the weight of my upper and lower sections and where my pivot point ends up. it'll depend a lot on choice of materials.
I've got a hybrid design in mind, just finalizing the numbers.
the primary mirror from Orion optics is 5.6Kgs, so I have to keep weight down where possible.
with the forkmount, i'll need sliding type counterweights along two axes, have to factor that in as well.
with the string spider, have you ever noticed slack or is there sufficient tension to compensate with temperature changes?
how long did it take to build it from start to finish, and do you think there would be any benefit if the three central square tubes were spaced out a bit so the dovetail is fixed over a wider distance axially?
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Hi Alistair, thanks for your kind words. I built the scope during evenings over a period of a couple of weeks. I think I might have spent some 10-12 evenings on this in total. A lot of that time went with researching and trying out different things, so to replicate it would probably take less than half the time now.
I have never had any slack in the spider. It is not wire tension that keeps it in place, the wires are actually less tensioned than on a guitar, it's quite surprising. The design is simply such that the secondary holder cannot flex or move in any direction without directly pulling on at least 2 wires. This makes it much more rigid than a traditional vane spider which easily flexes around it's own axis etc. For example, I have not had to adjust collimation since I finished the build in April - it is still spot on.
Regarding the weight, I think my OTA, without optics, was 7.85kgs. The 10" optics added 4kgs on top of that. So if you instead make a 12" you could expect maybe 13-14kgs in total I assume.
Yes I think you could easily make the central cage wider if you are concerned about the dovetail. As it is, the dovetail is very sturdy though. I actually made mine inspired from another design which used only two central square tubes, so I had the same concerns and then added one. Maybe it wasn't necessary.
Regards,
Rolf