tubes for 12" dob OTA 13-14" dia. 60" long where?
Posted 08 April 2013 - 09:37 AM
Posted 08 April 2013 - 12:29 PM
Posted 08 April 2013 - 05:24 PM
Posted 08 April 2013 - 09:38 PM
Any more suggestions?
You could make a truss scope.
Sean, I'll second the truss scope build, unless you have a specific reason for a full tube design.
I'm sure you remember seeing mine at the last star party, much easier to travel with.
Posted 09 April 2013 - 08:29 AM
Posted 09 April 2013 - 10:01 AM
Sonotube, by the way, comes in 12 ft lengths, which should be plenty long enough for the OP's scope.
Posted 09 April 2013 - 11:04 AM
I may just lengthen my current tube a bit and remove the dents and dings from it. I could just make a dew shield like device to help block stray light. I don't know if I want a paper tube and the plywood tube is nearly $300.
Posted 09 April 2013 - 02:17 PM
I don't know if I want a paper tube
my 10in dia tube is fine, just soak the ends in expoy. fill the spiral seam with bondo.
Posted 09 April 2013 - 09:02 PM
Posted 15 April 2013 - 12:43 PM
I want a solid tube because it is easier for a first build, I can reuse most of my parts, there are less thermal issues, easier to hold collimation, and I like the alt clutch design that gso uses and I want to use it on the scope.
Just sharing my experience making a paper-tube scope a la stellafane's website and moving on to a 12" Truss.
Agree that the solid tube is easier to build, but there are some things the truss is just better at. My 2 cents:
1. Make sure the tube is stiff because placing the secondary sucks when the tube warps under tension. It is much easier on my truss because the rings are plywood.
2. Solid tube scope should have more thermal problems, because they hold the air current closer to the light path whereas trusses don't really have a tube to hold anything. Caveat: The mirror box has to be open at the bottom on the truss.
3. If you make your alt bearings large enough and balance your scope, you shouldn't have any need for a clutch. Personally, I hate the clutch on my 12" lightbridge (partly why I'm building the truss).
What I did is build a dob 4.5 from a $14 meade tube, then graduated to a 8 inch build with an 8 inch f5 mirror, now trying truss. I learned a ton, and made plenty of mistakes. I definitely benefitted from building the solid tube first -- mostly with regard to building the bearings.
Posted 15 April 2013 - 07:22 PM
Posted 15 April 2013 - 08:04 PM
IMHO Sonotubes are underestimated. They are inexpensive, light for their size, and adequately strong. I used sonotube for the 16 inch Cassegrain shown here. The tube is 18 inches in diameter, came in a 12 foot length for --- oh probably $60. Very hard to beat. As said earlier, soak the ends in epoxy, fill the spiral with bondo, finish with epoxy and paint. They can be made to compete with the smoothess of aluminum tubes, or crudely painted with house paint for functionality or anything in between.
I suggest you get a tube from a cement contractor supply for consistent sizing. Typical home supply shops use what they call "nominal sizing". an 8 inch tube can be a variety of diameters. That is so they can slip three tubes inside one another for easier shipping.
Posted 16 April 2013 - 08:14 AM
The reason I like the clutches is that my eyepieces vary in size so much that balancing the scope for all of them is not quite possible.
Oh, I see you have a paracorr. I've heard they are heavy and can make balancing a pain. I've been trying to avoid buying one because of $$. I'm at f5, so I'm getting by with lighter fare.
BTW, I didn't soak the end of my sonotube in epoxy as I see suggested here, so you may not run in to the "bendy" tube problem that I did when you try to place the secondary.
Posted 16 April 2013 - 09:44 AM