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How to make a plywood tube

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#1 pestras


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Posted 08 April 2013 - 08:17 PM

Hello everybody. I´m going to make a telescope with a 11" zambuto mirror, aurora cell and protostar secondary. In México there aren´t many choices for the tube (13" OD) so I would like to try a circular plywood tube. Someone has made a circular plywood tube? Is there a plan or book that shows how to do it?... I supossed it is made of several thin plywood sheets but are they glued between them?... I hope someone has more information on this topic. Thank you very much in advance...

Best Regards
Mexico City

#2 Chriske


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Posted 08 April 2013 - 08:48 PM

Look here it might give you a start.

#3 Pinbout


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Posted 08 April 2013 - 09:03 PM

Yeah, you could make donuts and vertical ribs the skin it wiggle wood, or bendy board. Then finish it with a veneer.

#4 RossSackett


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Posted 08 April 2013 - 09:20 PM

I think an octagonal tube looks classier and is easier to build.

#5 Achernar



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Posted 08 April 2013 - 10:33 PM

It's possible to make a wooden circular tube. I in fact have accomplished it, twice. But it's quite tricky, and you will need a table saw, and a way to guide the wooden slats through the blade while keeping your body parts out of harm's way. A table saw can be a very hazardoud machine when used improperly, it can sling wood at you with enough force to seriously hurt you, so if you don't know how, I would suggest getting help from a woodworker who can show you how to use the machine safely. I made formers from plywood with a circle the diameter of the outside of the tube, cut in halves. Blue painter's tape was used to hold the slats together, then glue was put into the vees formed by the beveled edges. This is a "coopered" tube becaue the slats are beveled with the wider side facing outwards. Once all the joints are filled with a liberal amount of glue, roll it into a cylinder, put the formers around it, one every 8 or 9-inches, and tighten some pipe or bar clamps, one on each side of each former until glue squeezes out along every joint line. This is very messy work, better not do this in your good clothes. Once rolled and clamped leave it to dry overnight, then you can remove the formers and blue tape. Sand the ridges and any glue off the outside and get the tube round and smooth. Then you can stain and varnish it. I stained the one I intend to use with an oil based stain, then topcoated it with exterior grade polyurethane, the only sort of varnish suitable for a wooden telescope, other than marine varnish used on boats. Use a straight grained kind of wood, preferably a hardwood such as clear Cherry or white oak, not plywood. I did make one from clear, straight grained yellow pine made into slats 1/2" or about 13mm thick. It is strong enough to support the weight of a 90 kilogram man standing on it, and yet it's lighweight. Otherwise, I would make it a hexagon or even a 12-sided tube with plywood, the joints reinforced with strips of wood beveled to match the inside angle. Whichever way you choose to make the tube, reinforce the ends to protect them from damage during handling or transportation. You will have to calculate how wide the slats and what bevel to use, so before cutting any wood, making a full scale drawing of the tube's cross section, then making a short test section is a good idea to avoid wasting expensive materials and time.

If on the other hand, you just want a durable tube that is easy to make, concrete form tube will work. Just remove the wax on the outside, and the liner on the inside, and seal it inside and out with oil based flat black paint on the inside, paint of the color of your choice on the outside. That could be white, glossy black, red, blue, or anything that strikes your fancy. You could even put wood verneer on the outside, then stain and varnish it. Again, reinforce the ends with end rings.


#6 plyscope


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Posted 08 April 2013 - 11:52 PM

Octagonal ply 6" f5 from about 10 years ago.

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#7 tim53


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Posted 09 April 2013 - 12:06 AM

I still need to finish my latest project - an 8" f/9 in a cherry tube that wound up being 20-sided:

My 8" f/9 OTA build

Here's where I left off:

Posted Image

It's pretty straight and round, too! I was about to build plywood rings to support the lazy suzan rotating rings and plan a sled focuser for it when we had to move out of our house and garages for a movie shoot in the house. That's done now, so I should get back to work!


#8 dcoyle


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Posted 09 April 2013 - 09:08 AM

Check out drumshells. It may be easier to fabricate joints for two foot sections than to fabricate the whole tube from scratch. I got mine from http://www.drumfound...rum-shells.aspx


#9 Jeff Morgan

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Posted 09 April 2013 - 10:02 AM

There is the strip plank method used by canoe builders. Also someone here recently used drum shells to build a tube.

#10 BluewaterObserva


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Posted 09 April 2013 - 10:15 AM


I did my 30" and an 8" refractor with something similar.
This makes it pretty easy to make very strong wood tubes.

Really great siffness to wieght ratio on the stuff.

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#11 rboe



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Posted 09 April 2013 - 10:42 AM

I would steer you towards drum shells, see the links for them in the pinned Best of ATM thread at the top of this forum.

Plan B; using a form like for wooden boat building, build each half then glue them together. This has the advantage of being lighter but the work factor is very high. So is the risk. :) Kinda depends on your wood working skills.

At 13" a truss dob is not out of the question either. You are at the awkwards place where you can either way. I think the truss dob would be easier for you in the long run if you are not set on a tube.

#12 tim53


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Posted 09 April 2013 - 11:27 AM

My fastest glueups are polygonal plywood tubes, though:

Posted Image

Cheap imported mahogany 1/4" plywood scrap I had left behind after a cabinet project ( Hatch Observatory )

Finished tube, after staining and bunches of poly layers:

Posted Image


#13 pestras


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Posted 10 April 2013 - 08:11 PM

Thank you very much to everybody for the ideas and comments. Maybe the polygonal tube will be my option....I will began to do the plans

Best regards

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