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jeffg
member
Reged: 02/13/07
Posts: 40
Loc: Irvine CA
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I like the design--very straight forward and simple. Do you have a method to allow for rotation of the secondary if one needs to adjust that? Gluing things on exactly straight has never been my strong point. I've made a few curved spiders and some tension against the tube wall seems to be needed in the curve of the spider to keep vibration from becoming a problem.
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Jeff
14", 10", & 4.25" Dobs
8" Schmidt Newtonian, C-8 SC, 8" LSC
6" Cave Student Model A, 6" Dall-Kirkham, 6" RV-6
5" Refractor & 80 mm Folded Refractor
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marcink
member
Reged: 08/01/07
Posts: 67
Loc: Lombard (Chicagoland), IL
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Ryan - there is no need for a center bolt indeed. I thought I would have to put it, but after assembling the holder, the whole thing is really stiff. I think I am going to use a thicker vane to add rigidity. I am planning to attach it to two thumb bolts on each side and let those bolts through alum tubes of the secondary cage. Nuts on the other side of the tubes would tighten the whole thing pretty well. You mentioned springs to make the vane stiffer - how would you use them?
Jeff - I haven't thought about rotation, but I think I could adjust it by rotating the vane sligtly by loosing thumb screw nuts on one side and tightening them on the other. How did you solve it? You said, you've made curved spiders before - how did you bend the vanes?
I think is crucial to make a spider very sturdy - you rarely collimate secondary. In the scope I use, I adjusted secondary only at the beginning and have never touched it after that..
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8" Chest Newtonian
Lombard - orange skies of suburban suburbia
Green River - where I breathe stardust
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jeffg
member
Reged: 02/13/07
Posts: 40
Loc: Irvine CA
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Both of my curved spiders had a center bolt so I could rotate the secondary to match the axis of the focuser. But as you say, one could also rotate the curve of the spider around the inside of the tube to accomplish the same thing. But the scopes I put them in had square tubes, so that really wasn't an option. Bending the curve in the spider was done using a circular piece of plywood slightly larger than the inside tube diameter. That left some tension in the spider curve when I installed it.
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Jeff
14", 10", & 4.25" Dobs
8" Schmidt Newtonian, C-8 SC, 8" LSC
6" Cave Student Model A, 6" Dall-Kirkham, 6" RV-6
5" Refractor & 80 mm Folded Refractor
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jayscheuerle
Carpal Tunnel
Reged: 01/16/06
Posts: 2952
Loc: S. Philadelphia, PA
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I don't think that rotating the secondary is really necessary, as long as it's close enough that the entire primary is visible (you're getting all the light).
If you think about the secondary as a mirrored plane, then all that rotating it does is change the angle of the plane, which can be accompanied by adjusting the collimation screws. If your depth set correctly, you really only need 2 of those as well. - j
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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