Fiberglass tube construction

I’m looking for some advice regarding the construction of a 40” 9 1/4” ID fiberglass tube. I had planned to place a plastic sheet over a 9 ¼” sonotube (which will not be part of the tube), cover with resin, and incrementally apply 3 layers of fiberglass mat cut to the exact length and with perhaps a 1/2 inch extra diameter for a slight overlap. Essentially I’d follow the instructions posted at http://www.atmsite.org/contrib/Kohut/fgtube. I could also simply apply 1 layer over the sonotube (including the sonotube as part of the construction), although this combination would probably be thicker than I had desired. Also, are there any special considerations for cutting holes in fiberglass (for the focuser)? Thanks for any help.

Sean, in a few words,"been there-done that!" But I don't have the tee-shirt!
I built a fiberglass tube as per the method described in Neale Howard's book, "Making a Telescope". One word description, MESSY!. And a LOT of work.
I polyurethaned and then painted sonotubes for 6", 8" and 10" newts. Very efficient and reasonably light weight. If you put an aluminium ring as a stiffener at the points where the diagonal and mirror cell mount, you gain a lot of rigidity with little additional weight. Effective.
My recent 8" f/6 ota was sonotube with two outer layers of fiber and resin and one inner layer of resin. Very strong but the thickness and weight started to add up.
My current 10" f/6 (12.2" OD) sonotube and heavily glassed inside and out would probably allow me to walk on top of it (all 245 lbs), but it is HEAVY, and I am at the age that I begin to notice unfortunately.
A fellow club member recently procurred a 12" x 60" aluminium tube. With flocking interior, a good automotive exterior finish, and edge guard end rings, it is the consumate tube in my opinion. Lighter than my monster, probably as effective at heat disipation, and a few pounds lighter. That's my next trip, if there is a next!
FWIW

Walt

Sean, I recently added a layer of fiberglass to the outside of my sonotube to stiffen it up a little. While preping it I came up with a different way of doing it, but have yet to try. The "good" sonotube has a layer of plasitc inside that is meant to help release it from the concrete that is pored into it. I figured I could lay a couple of layers inside the tube, these would be the inside of the scope so wouldn't have to be perfect, but relatively good. Then peal the cardbord off of the fiberglass. The last layer sholud release from the fiberglass easily. Then a little sanding and another layer or two of fiberglass, taking care to get a good layup and you should have a decent tube. A good epoxy paint on the outside and you couldn't tell it from a parks tube!

I've done some work with fiberglass, and it was no fun at all. Actually, true Sonotube is quite stiff, and if you add some wooden end rings to both ends, it is extremely stiff.

A good way to finish Sonotube is to leave the outside wax on the tube, and cover it with cloth. Hoffman fabrics makes some very nice fabrics with celestial themes, You can put it on with a thin layer of white glue and the spray it with Scotch Guard. End rings on both ends and you are done. Looks great and is quite easy to do.

The best tubes, IMHO, are unpainted aluminum. You can "jewel" the outside to make it look nice, and you will have no worries about scratching a nice paint job.

I solved the wax problem, and the problem of the "logo" on the tube by removing the outer layer of paper. This also solved the problem of the little lump where the outer layer of paper overlaps as they finish the outside of the tube. I also removed an inner layer of paper, to get rid of the plastic/wax that coats the inside of the tube. This had the added benefit of leaving a rough/fuzz on the inside of the tube, which with a coat of flat black paint kinda resembles flocking paper but isn't quite that good.

Removing the wax is way too much work. Leave it on, cover the tube with cloth, and things are very simple.

Keller makes maple plywood drum shells and cylinders (available from Anderson Internation Trading). The cylinders are sold in lengths of 27", 48" and 96" (exotic veneers available); the drum shells in various sizes. I'm considering a 13D 9L drum shell for the secondary cage of an 11" f/4.5 former StarHopper. Thickness goes up to 10-ply, 0.27" for the 100% maple drum shells, up to 7/16" for cylinders.

Has anyone any experience with these plywood tubes, or general comments/suggestions?

-- William