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derangedhermit
journeyman
Reged: 10/07/09
Posts: 6
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It seems to me that a rocker box could be stronger and lighter if the rocker box was cylindrical, with a cutout for the tube / mirror box. It would seem to line up the azimuth forces better with the rocker structure, so it would flex less. For example, a 16" sonotube, maybe doubled in thickness and glued, for a 12.5" mirror (approx 14.5" tube). The azimuth bearings would have to be wider than with the typical rocker box.
Has anybody tried this? Could it potentially be developed into a low-cost, easy way to build a rocker box?
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Jeff Morgan
Carpal Tunnel
Reged: 09/28/03
Posts: 1987
Loc: Prescott, AZ
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An arc is very strong, but only when loaded in compression. My guess would be that it would not work as you think. It would still result in an open structure, which is not very resistant to twisting forces (which is what happens when you push a Dob in azimuth).
Then again, experience is the best teacher. Give it a try. Perhaps a large diameter section of sonotube, split in half and reinforced with fiberglass?
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Jeff Morgan
Prescott, AZ
Wile E. Coyote School of Telescope Making
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NHRob
Post Laureate
Reged: 08/27/04
Posts: 3157
Loc: New Hampshire
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Interesting. Getting the altitude bearings to fit well with the structure would be more challenging.
Rob
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Rob
**********************
Canon 12x36 IS binos
TEC-140: #433 on CGEM
Faworski orthos (7,10,16.7mm)
stuff ...
no free time ... lots of clouds !
" Life is what happens to you while you're busy making other plans" !!
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derangedhermit
journeyman
Reged: 10/07/09
Posts: 6
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Quote:
Interesting. Getting the altitude bearings to fit well with the structure would be more challenging.
Rob
A little. A shallow circular router plunge cut into a plywood base would give a good attachment point for gluing down the rocker tube. Then, as you say, attaching the 4 teflon points in a good way would be next.
I think Sonotube azimuth bearings would be worth a shot for this, since they would need to be 2-3 inches wide.
Two plywood circles for ground board and rocker base, three diameters of sonotube, some hardware bits, and you have a telescope structure.
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derangedhermit
journeyman
Reged: 10/07/09
Posts: 6
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Quote:
An arc is very strong, but only when loaded in compression. My guess would be that it would not work as you think. It would still result in an open structure, which is not very resistant to twisting forces (which is what happens when you push a Dob in azimuth).
My intuition says a round tube is more resistant to twisting than a square tube. But it may not be so.
You are right about it remaining an open structure, of course.
If a rocker tube turns out to function no better than a rocker box of similar weight, it still might become an appealing alternative.
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grendel
sage
Reged: 04/12/09
Posts: 249
Loc: Canterbury, Kent, UK
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well therer are other ways to use tubes to make mounts- see two of mine here in this picture
grendel
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