Round Wooden Tubes?
Posted 30 November 2010 - 09:56 PM
Posted 30 November 2010 - 10:15 PM
Posted 30 November 2010 - 11:01 PM
I remember that thread, and wondering what happened to it. I'm sorry to hear he wasn't able to finish it.
I've been cogitating about how to go about this. It does seem as though the best way to get a round tube would be to start with a coopered tube and sand it round.
I've always made faceted tubes out of plywood so I wouldn't need to build a form before building the tube - I just tape up the slats on a flat surface, put glue in the joints, and roll it up to dry. This is fine if you don't need to rotate your tube. But if you do, fitting rotating rings to a polygonal tube is harder than it might sound (see my own recent experiences with this here .
Of course, if you don't need to rotate, polygonal tubes aren't a problem at all.
So, I'm thinking that I might try making a coopered tube for a small refractor project I have waiting around. The tube would be small enough that I could turn it on my Harbor Freight wood lathe (12x36).
I'd also be interested in hearing others' experiences making round wood tubes.
Posted 01 December 2010 - 08:47 AM
Posted 01 December 2010 - 09:42 AM
You could make a couple grooves that are round in the areas you want the rings in. But sanding it round after the fact would work too. Just a lot of work!
I agree. Probably a better way would be to make a jig to support a router, and turn it round with a router instead of a sander.
I thought of using thin, bendable plywood, too. But the cost would have been 3 or 4 times that of a single sheet of 1/4" plywood.
Posted 01 December 2010 - 10:15 AM
I bought a router bit designed to cut a bird's mouth in one side and then you can glue it up from there.
Posted 01 December 2010 - 11:00 AM
Tim; jig and router sounds like the cat's meow.
Posted 01 December 2010 - 11:13 AM
Posted 01 December 2010 - 11:16 AM
Please remember that I am drawing upon something I read in the early 1970's.
I did make a tube out of cherry in the early 90's out of a 16 sided polygon that I cobbled together.
I have a industrial wood lathe and used a rasp to get the roundness about right, and successive grades of files and then sandpapers to complete the job.
The cherry was 3/4" thick. The tube 7.5" in diameter and 20" long.
I disassembled and refigured a 6" f/6 portrait lens and made an RFT refractor out of it. Still works great.
Posted 01 December 2010 - 11:57 AM
i have made several wooden round tubes for newtons of 6" up to 16".
Here are a couple of picture of a 15" tube.
I use normal plywood for the rings and "airgraft plywood"(thats how they call it here) of 1mm thick.
For the piece that need to be stronger (mirror cell ,focuser) i use 2 layers of 1mm.
Very strong and lightweight.
Posted 01 December 2010 - 11:58 AM
I made the shell in my 15-inch Dob's upper cage from 1-inch beveled wide slats of plywood. I used blue painter's tape to hold them together on the outside, then put glue in the gaps. Then I wrapped the assembly around a mandrel made of wooden disks of the desired inside diameter and used web clamps to hold the slats in place until the glue dried. All you need do is figure out the circumference of the tube on the outside, how many slats you will need and their width, then the angle of the bevel necessary. Use a table saw and push sticks to make the slats. Titebond or any other similiar yellow wood glue is an good choice for bonding the slats together. If you want to stain and varnish the tube, use a solid hardwood such as oak or cherry, and be careful to remove all traces of glue on the outside before staining. Always use an exterior grade polyurethane if you opt to varnish it, because other varnishes, shellacs and lacquers will rapidly degrade and fail.
That's similar to what I did with my 10" f/6's tube, but I should have made mandrels to force it rounder than it is.
Posted 01 December 2010 - 12:15 PM
Posted 01 December 2010 - 12:40 PM
John, keep us posted on the birds mouth bit project. I see those bits for sale and I'm always tempted but have not pulled the trigger.
Tim; jig and router sounds like the cat's meow.
I got the wood two years back at a store. They were blowing it out because it had gotten water-damaged. It turned out to be spalted maple. The fungus creates interesting patterns in the wood.
Its all ripped and planed to the right thickness, I just have to get my ambition together to work in my cold shop for a few days.
The bit came from Lee Valley. They come in different types. Mine can do either 6 or 12 sides. To do 6 or 16 sided objects, you need separate bit for each.
You can also do conical forms using tapered staves.
Posted 01 December 2010 - 12:42 PM
Here's one I made in a similar manner to the 10"er's tube, but using solid stock vermillion padauk, resawn on my bandsaw and thickness planed to 1/4" thick. This was to be for a 5" f/5 refractor, but I'm starting to think I should leave the lens in the PVC tube it came in (probably dates to the 50's or 60's).
Do you have photos inside the ends? I always like seeing how wooden constructs are put together inside.
Posted 01 December 2010 - 12:51 PM
Posted 01 December 2010 - 12:54 PM
One could make more or fewer-sided tubes by building a jig to feed the work into the router bit at an angle to the table. I've thought about doing something like this, since I like odd-numbered polygons.
Posted 01 December 2010 - 08:25 PM
I did as tim5.3 did, just taped the outside faces, spread glue on the cuts between, pulled them together and let dry.
I was also very skeptical this would support any large amount of weight.
It dryed for a few weeks and then I pushed it down on the floor and finally STOOD on it without it breaking. I actually had to jump on it to get this short section ~16" or so to fracture. The glue failed.
Posted 01 December 2010 - 09:25 PM
http://www.aitwood.c...all Paint Grade
Click on Millwork Components, then Plywood Cylinders to view all the sizes they make.
Posted 01 December 2010 - 11:30 PM
I made my Cass's tube similarly, a few sides at a time. But I had longitudinal ribs (corners, really) to define the angle between sides. I did it this way to avoid having tube currents cascading off baffles inside the tube and into the light path, which was a problem I had on a prior tube for those optics: Cass thread
Posted 01 December 2010 - 11:59 PM