> From: David Boll <dboll@hp-vcd.vcd.hp.com>
> Subject: Fiberglass tubes
> Date: Sun, 7 May 95 9:00:39 PDT
> 3) I'm thinking about getting some pigment from a marine supply
> place, and coloring the tube, to make it some kind of cool-looking
> auto or boat color. But, I'm also concerned about making the tube
> block light. So, maybe a layer of black construction paper
Why not spray paint it? Fiberglass/polyester-resin will take black auto body primer, and you can spray a coat of some finish color over that. It works just fine for auto body repair, so why not with a scope tube?
> 4) How thick does the resulting tube have to be? I'm currently thinking
> 2 layers of cloth/resin, then a light shield layer, then as much
> resin as I can put on it.
No need for a light shield if you spray paint the outside, & spray paint the inside black.
Another thought: 1 or maybe 2 layers of fiberglass cloth (cloth overlaps a few inches, so no weak seams), followed by a layer of 1/8" balsa wood glued in place with polyester or epoxy resin, and then fiberglass over the top. Should be quite strong, rigid, and very light weight. You don't need a very heavy resin coat on top. Why carry around excess weight? The glass cloth provides the strength, and the balsa wood separates the two strong, thin shells to provide _MUCH_ more rigidity.
Balsa wood is a little on the expensive side, so using it only makes sense if you want a very nice, light, rigid tube, and you're not trying to make the tube as cheaply as possible.
A few days ago, I finished making a cell for a mylar solar filter, using this tube-making stunt. It works well. The trick is to wrap the balsa wood tightly over the first layer of fiberglass & clamp it firmly in place while the polyester hardens (maybe covering it with polyethylene sheet, and then wrapping the thing with masking tape??).
Myself, I taped a layer of hardwood veneer to the round form (made from foam core, hot-glued together), using carpet tape (sticky both sides) between the veneer & the form. Then I fiberglassed over the veneer, & sanded it after it had hardened. Then I epoxied on balsa-wood strips, wrapping the thing with polyethylene sheet & then wrapped tightly with masking tape, & waited for the epoxy glue to harden. Then I sanded to remove the glue spots & shape the balsa wood, and fiberglassed over the top.
If I do this sort of thing again, I'll lay the balsa wood on in a single, continuous sheet, to avoid the epoxy seams between the balsa strips. These seams added some unnecessary weight, and made sanding the balsa wood more of a chore than is necessary. Balsa wood comes in rather small sheets, but you can epoxy them together at the edges to make any size sheet you need. Press the small sheets together firmly, to squeeze out as much of the epoxy glue as possible, & wipe off the excess. Use slow-cure epoxy, not the 5-minute stuff. You'll need the longer working time.
BTW: You can make strong, thin plywood by stacking up layers of hardwood veneer (alternating grain directions), bonding them together with single layers of fiberglass cloth soaked in polyester resin. Press firmly or clamp to squeeze out as much excess resin as possible. (I cover the stack with polyethylene sheet with a sheet of plywood on top, with a heavy weight on top of that.) This might also be a good way to bond together ordinary plywood, particularly if you build up a thick stack from sheets of 1/4" plywood. With an additional fiberglass layer over the top & bottom, the stack should be quite rigid and very resistant to warping. Ordinary wood glue does not work well with such sandwiches, but epoxy glue works great, and polyester resin should also also work.
Thank you, Bratislav Curcic, for the idea of using balsa wood! This is absolutely great stuff!
-- Gerry