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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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Ok, fellas (and gals who might be interested)... Using Google Sketchup, I've pretty much finished a 3d model of how I intend to build my telescope. It will be constructed of a combination of 1/4" and 1/2" plywood. The panels will be glued together and screws will also be strategically placed. My preference is to build it so that the mount can be taken apart for ease of transport. I intend to put it together with a combination of pegs and wedges so it will be sturdy. However, if it proves to be impossible to keep it steady, it can be permanently assembled with minor enhancements to the design. The tube is 56" long and the base is 27" wide. I have tried to minimize the dimensions and made cutouts to minimize the weight as much as possible. I would appreciate your input regarding whether I have design flaws that need to be addressed before I start cutting the wood and building it. A number of photos of my model are posted below. Your input is appreciated...
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Building a f5.24 10" Dob
in an octagonal wood tube
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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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#2
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Building a f5.24 10" Dob
in an octagonal wood tube
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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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#3
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Building a f5.24 10" Dob
in an octagonal wood tube
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plyscope
sage
Reged: 11/23/06
Posts: 327
Loc: Perth, West Australia
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Very interesting design. Why not eliminate the middle pair of tube rings? Also why not orient the tube with the flat sides parallel to the mount sides rather than the peaks? Perhaps the altitude bearing cradles could be smaller on the external size also.
I hope I don't seem negative, I am curious.
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Andy
6" f15 refractor
90mm f16.7 refractor
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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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Oh, not at all...your critique is appreciated. The middle tube rings are there because screws will be going through the sidebearings, the boards they are attached to and into the rings. I thought this might make it sturdier. I was just going to put one in the middle but I thought 2 might be better but I wasn't sure about this. If you think this is unnecessary, please don't hesitate to say so. The rings will not be permanently attached to the OTA...they will be clamped around it. As for the orientation of the tube within the rings...I did it this way for aesthetic reasons. I wanted the octagon of the OTA to appear rotated with respect to the rings. I would definitely consider changing it if you guys think this might cause me some sort of problem.
P.S. I based my tube rings on those of another scope that belongs to my astronomy club...see the pic below.
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Building a f5.24 10" Dob
in an octagonal wood tube
Edited by dreamregent (11/05/09 05:14 PM)
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plyscope
sage
Reged: 11/23/06
Posts: 327
Loc: Perth, West Australia
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I don't see any problems. The beauty of plywood and atm/diy is that you can modify it later if you need to. That is part of the fun!
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Andy
6" f15 refractor
90mm f16.7 refractor
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m. allan noah
member
Reged: 08/14/09
Posts: 19
Loc: Virginia, USA
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my $.02? It's a little overbuilt:
1.you dont need the tube rings, that OTA is going to be really strong without them. just put the blue plates right on the side of the OTA, and slot your alt bearings if you need fore/aft adjustment. if you really want more bracing, make some 1/4 inch baffles glued to the inside. then no-one can see how hard it is to make all 8 edges line up 
2. use more circles. I know the polygons are a bit of a theme given the shape of the OTA, but honestly a circle cutter on a router is MUCH easier than all those angles. It will also make things like manual setting circles easy to install.
3. the spokes on the base plate are not saving you much, just cut three round holes if you want to save weight, or better, use a ring of lateral bearings instead of a central bolt, and you can cut the plates into rings.
4. I would increase the diameter of the base plates, looks top heavy.
5. the angled 'sort of circular' brace on the front might look nice, but it's not nearly as strong, light, or stable as a simple square with some studs and wingnuts.
allan
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dreamregent
sage
Reged: 04/06/09
Posts: 454
Loc: Clearwater, FL
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Quote:
my $.02? It's a little overbuilt:
1.you dont need the tube rings, that OTA is going to be really strong without them. just put the blue plates right on the side of the OTA, and slot your alt bearings if you need fore/aft adjustment. if you really want more bracing, make some 1/4 inch baffles glued to the inside. then no-one can see how hard it is to make all 8 edges line up
2. use more circles. I know the polygons are a bit of a theme given the shape of the OTA, but honestly a circle cutter on a router is MUCH easier than all those angles. It will also make things like manual setting circles easy to install.
3. the spokes on the base plate are not saving you much, just cut three round holes if you want to save weight, or better, use a ring of lateral bearings instead of a central bolt, and you can cut the plates into rings.
4. I would increase the diameter of the base plates, looks top heavy.
5. the angled 'sort of circular' brace on the front might look nice, but it's not nearly as strong, light, or stable as a simple square with some studs and wingnuts.
allan
Thanks for the input... Your suggestions have prompted some changes.
1. I considered eliminating the tube rings because of the extra weight but I didn't like the look of it. I talked to the cabinet shop I'm buying the 1/4" cherry plywood from...they weighed the whole 4x8 sheet and told me it weighs 25 pounds. The ota will use just less than half of that so I roughly calculated the whole ota should weigh 30 to 40 pounds with the rings and the hardware installed...not the lightest thing in the world but I can easily manage it and it will be prettier to my eye. I'm going to add a couple of baffles though. If they only intrude 1/4" into the tube, I'm thinking the currents will still be able to get around them in the top corners without going into the light path. Just to be safe, I'm thinking that I might add a fan, tho.
2. Your suggestion of using more circles is well noted. I'll be making a couple of changes along this line. I already have a digital level to use for the altitude measurement so that's not a problem. I thought I already had a solution for the azimuth circle but I believe I've got that backwards after reading your post and thinking about it. Luckily, a minor change is all that's necessary to correct that problem.
3. Considering the area of wood that I already have cut out in my design, I don't think cutting circles would take out much more wood from the base plate & ground board...it would be about the same give or take. The angles might be more difficult to cut than a circle but I like the look of them. However, your suggestion of using lateral bearings is interesting and appealing to me. But, I don't know where I would get such a thing. I did a search on lateral bearings and found patents for them but I didn't see where I could buy them. Do you have a source on-line where I could take a look at them?
4. I was afraid of this and will increase the diameter per your suggestion. The base plate and ground board in my design are 27 inches on the points. I am keeping the octagon shape for them. How wide do you think I should make them...30 inches, 32 inches, or more?
5. I wasn't sure about this part because of how I would connect it considering that I want to be able to take the mount apart. However, your solution sounds like a good idea to me.
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Building a f5.24 10" Dob
in an octagonal wood tube
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joe colontonio
sage
Reged: 03/02/06
Posts: 206
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A larger Alt bearing will make having a broad range of ep weights easier to balance without sliding the ota each time.
Look at discovery telescopes for inspiration on sliding bearings.
Have fun and enjoy.
Make sure you can fit another person (niece)in the car with the scope.
Joe
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