Tom L
Reged: 01/07/04
Posts: 29817
Loc: Sunny Oregon
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If you are going to be a snob about it, go buy the bible (Kriege's Dob book) and study it. Nothing wrong with want a solid scope...but if it is appearances that bother you...well...you could always paint it black...then it would look like a Discovery (kinda-sorta).
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Tom 
Tele Vue 102mm f/8.6 on an EzTouch
Vixen 80mm f/5 A80SSWT on a grab-n-go mount
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erik
telescope surgeon
Reged: 01/30/04
Posts: 24019
Loc: Hawaii 19 N lat -155 Long.
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well, here's kind of what i was thinking of. sorry, it's a bit sloppy...
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
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rboe
Numbfinger
Reged: 03/16/02
Posts: 39729
Loc: Phx, AZ
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I'm a big fan of the bayanet mount. Like your SLR camera lenses. Consider that to twist and lock your upper to the lower sections. A poor man's bayanet would be a couple pins that fit into grooves in the other section. A router would be needed though.
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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Tom L
Reged: 01/07/04
Posts: 29817
Loc: Sunny Oregon
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I like the idea but I'm afraid the straight poles will cause it to droop. The truss design sets up an opposing set of forces that keep the structure ridgid, the straight design has to rely totally on the strength of the poles themselves. There is additional weight here that will add to the burden. What if you added some cabling between the poles in an X pattern to help offset the load?
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Tom
Tele Vue 102mm f/8.6 on an EzTouch
Vixen 80mm f/5 A80SSWT on a grab-n-go mount
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erik
telescope surgeon
Reged: 01/30/04
Posts: 24019
Loc: Hawaii 19 N lat -155 Long.
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that's what i was afraid of, whether the straight trusses would allow sagging. i was thinking that because of the shorter length due to the two sections, it might be okay. but maybe not? i guess i could try a more traditional truss design, although a cable or even a "crossmember" truss of some sort might work...
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
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MMICKELS
Aluminum Knight
Reged: 01/20/04
Posts: 25190
Loc: The Land of Shake and Bake
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Erik, where will the Alt bearings go? I would consider some sort of light sheild on the upper cage opposite the focuser if the upper cage is meant to be that short. If you make this into a truss, you'll find cool down to be quicker and tube currents will vanish.
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Mark
"The only thing wrong with immortality is that it tends to go on forever."
Herb Caen
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rboe
Numbfinger
Reged: 03/16/02
Posts: 39729
Loc: Phx, AZ
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Eric;
Just to brain storm a bit here, I see from your drawing you intend to mount the bearings on the lower cage. Gut feeling tells me you will have balance issues with out adding a lot of counterweight to the lower cage.
So; one way around it and keep the general idea of what you have going here would be two plywood "slabs" going from the lower cage to the middle ring - one per side. These slabs would have grooves along the length for the mounting hardware for your bearings. Having grooves would allow you to tune the balance point depending on the eye piece being used.
I would imagine in practice the grooves would only have to be a few inches from a neutral balance point so you could machine them after that was found.
The slabs could be 1/4" birch ply with edge stiffeners and you could have cut outs to keep the weight down - or just to have a design.
These slabs would be removable just like the poles and would replace all the poles used in the lower assembly. In fact, you could epoxy a pole on either side of the slab so the plywood acts just like a gusset. The whole assembly would be stiff enough that you could still use straight poles on the upper assembly.
You could also get cute and instead of a pole for the top edge on the slab just use more plywood with round holes drilled in it. This would be an instant eye piece holder.
Plan B: Go with a solid lower assembly but the tube would be in quarters length wise. Dissassembled they would nest together for easier storage. Assembled they would make a very strong tube to mount the lower cage (or perhaps a very truncated mirror cell) and the bearings. It would be a challenge to build however. It would offer up an extended dew shield effect, light sheild.
Someone makes plywood tubes so all you would have to do is glue on four sticks of wood where they will mate, epoxy the whole mess then cut apart with a very narrow kerf saw. Make up a little jig for the cut and it would be perfect.
Time for more coffee! Hopefully this got your juices going if it didn't scare the heck out of you! 
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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erik
telescope surgeon
Reged: 01/30/04
Posts: 24019
Loc: Hawaii 19 N lat -155 Long.
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great ideas, guys, thanks! as you can tell by my drawing, i obviously haven't taken everything into consideration yet. with my base, i didn't even draw up plans, i just started measuring and cutting. the ota is going to take a lot more thought. i was worried about the balance, so i think i will mount the hubs higher up. that will work well anyway, since i want to use the base that i just built. i was even considering building one section oversized so that you could install one section of the ota inside the other section for transport. but that would involve redesigning the base to accomodate the larger diameter tube section. unless i made the top section oversized instead, but then it would look a bit strange..... so much to think about! 
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
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Tom L
Reged: 01/07/04
Posts: 29817
Loc: Sunny Oregon
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...or you could paint the original tube black and not worry about for awhile...then build a true truss scope.
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Tom
Tele Vue 102mm f/8.6 on an EzTouch
Vixen 80mm f/5 A80SSWT on a grab-n-go mount
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erik
telescope surgeon
Reged: 01/30/04
Posts: 24019
Loc: Hawaii 19 N lat -155 Long.
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no matter what i do, i'm not going to be satisfied! i think i need to own every scope ever manufactured to be happy... 
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
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Tom L
Reged: 01/07/04
Posts: 29817
Loc: Sunny Oregon
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I hear ya...
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Tom
Tele Vue 102mm f/8.6 on an EzTouch
Vixen 80mm f/5 A80SSWT on a grab-n-go mount
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jdickson
professor emeritus
Reged: 04/26/04
Posts: 685
Loc: Desert Hot Springs, Ca
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Quote:
no matter what i do, i'm not going to be satisfied! i think i need to own every scope ever manufactured to be happy...
It's all the rainy weather and having a new jigsaw 
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Joe
10" f5 ATM dob, 20x80 p-mount binos.
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erik
telescope surgeon
Reged: 01/30/04
Posts: 24019
Loc: Hawaii 19 N lat -155 Long.
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yeah, that must be it! let's see, what else can i cut.... 
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 10960
Loc: Los Angeles
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Erik,
The advantage of a truss tube, notwithstanding the easier transportability, is the dramatically lowered center of gravity. This can shorten the rocker box appreciably, adding to stability.
A truss tube dob, in this size, doesn't need to have the top and bottom in two section, because the poles won't be that long. To extend from the mirror box to the UTA, even a short one, the tubes will easily fit in a bag no longer than a decent size rifle. The whole ensemble could weigh under 80 lbs with a judicious choice of materials, and still be more rigid that your current setup.
I just viewed through a 15" f/4.5 truss-tube dob that broke down into sections that all fit in the trunk of a mid-sized car.
Since you have that new saw, you can easily shorten your rocker box if the new tube assembly has an appreciably lower center of gravity.
But your sections would be shorter, more easily stored and transported if you stuck to a 3-section, truss-in-the-middle design.
I almost hate to say it, but you could use the old sonotube for the UTA, with a repaint, and maybe a little stained wood for aesthetics. Make the UTA from kydex, aluminum pole pieces, and thin plywood, and your center of gravity goes even lower, shortening your rocker box, and reducing overall weight.
One good idea to keep in mind: At the top of the inside of the new mirror box, if that box is square, put a round baffle to cut down on reflected light from the insides of the mirror box, and to shield the mirror from light entering at the corners of the box (the places the shroud doesn't cover).
But, for easy transportability, think:
1) light UTA
2) short rocker box
3) low center of gravity.
You've probably looked at the designs already, but I'd be tempted to even use the "flex-rocker" design to lower everything even more. You'd do almost all of your observing sitting down! (much more relaxing than standing).
Keep on thinking!
No hurry, since you already have something functional (albeit heavy).
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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erik
telescope surgeon
Reged: 01/30/04
Posts: 24019
Loc: Hawaii 19 N lat -155 Long.
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thanks don, more things to consider...
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
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rmcpb
Carpal Tunnel
Reged: 11/16/04
Posts: 1568
Loc: Blue Mountains, NSW, Australia
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Glad I found this thread. I think I will change the design of my latest creation and go for the double set of short tubes. Probably will keep them attached to plywood disks in the centre and the bayonet fitting sounds like a beaut.
Keep the thoughts coming :-)
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Rob
8" & 13" Dobs
Equatorial Platform
Couple of Panoptics and a handful of BO/TMBs
9x60 binocs
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