Let me say up front this is all hypothetical, because there's no way my wife will agree to let me start another project at this point...

However, I wondered if anyone had experimented with building a foam-cored plywood skinned frame or any other radical materials. Anyone?

My thinking was that most people have the tools for this type of construction laying around, even if they're not bike people, so it might be a good way for us would-be hobbyist builders to cut their teeth. A brazed steel frame on the other hand would require the purchase of tools to miter the tubes at the very least (so probably a drill press and hole saws). I do own a dremel, and yah, I could technically grind the miters down to the right shape that way, but it would be very tedious.

Just a guess, but I'd think the bending radius of even the thinnest steam softened wood veneers would limit the frame "tubing" to fairly large diameters.

Renovo builds wooden bikes by splitting a hardwood frame in half, routing out the center, then epoxy glueing the two halves back together. I saw one at NAHBS last year in Portland, and it weighed a little over 17 pounds. Very impressive.

That's the reason I build in bamboo; I don't have any welding equipment or skills.
I do have a drill press, pipe miter jig, a ban saw, a drimmel, a couple of buckets of West System resin, and a flat table.

I find that bamboo is an inexpensive, easy, and forgiving way for me to dabble with framebuilding.

I used to stiffen racing canoes (C1) with honeycomb balsawood panels set between 6 ounce layers of figerglass and epoxy resin. Maybe balsa frame members sheathed in very thin CF.

Woodstrip boats of glass-wood-glass are very strong. Western red cedar is tops for strength-to-weight.

I'm building the rear of my next bike out of balsa core. I'm using it instead of foam because I have it in the shop already. I may also use spruce dowels for the seat and chain stays' cores since I'm not worried about weight, just proof of concept.

On a side note, I bought some plywood to make the I-beam for my bidarka build.
Any tips on sourcing the cedar?

Just had a different thought. Try making a test piece like this. Wax up a broomstick or any smooth dowel of appropriate diameter. Wrap a layer of 4-8 ounce fiberglass cloth and wet with epoxy. Then wrap sheets of newpaper around the whole thing and soak all the layers in epoxy. Be very carefull and make the wraps neat with no air voids. Wrap the paper to about .100 or one tenth of an inch. Finish by wrapping another layer of glass on the outside. Let cure. Pull off the dowel and weigh a given length so you can figure out what a frame might weigh. Do destruction tests on this glass and paper tube.

If nothing else, you'll be able to eliminate one more idea.

Yes. In the early seventies I built a 10' dinghy using WEST epoxy and western red cedar veneers layed (laid... spellcheck doesn't like layed) up 90° to each other and ~45° to the keel. I finished it with fiberglass cloth saturated with epoxy resin over both the outside and inside layer to seal the moisture content and protect the wood from rot. The last I heard (a couple of years ago) it was still going strong.

AllenG: I never had any problem getting western red cedar at any lumber yard. I guess it is used in many ways. Seems to be common wood. White pine is very good too, but about 10% heavier than cedar. When using red cedar you'll find the darker heart wood is actually lighter in weight than the lighter growth ring material. Odd, but true.

This is called cold molding and it is about the strongest hull a guy can put together. Nothing short of a steel hull or some large commercial fiberglass boat is stronger. And the cold molded boat will be much lighter. Until CF was used, this is how all America's Cup racing boats were built.

I checked out the Renovo link, and those are absolutely gorgeous. But, is that 17 pounds for just the frame?

That would be the whole bike.

I agree. My thinking was to have a the tubes the same width as the the BB.

I'm sure there are countless possibilities on material. Thin CF would be a great material over balsa, foam, or just about any other core. So would slightly thicker GRP and/or kevlar. I've never built anything using resin reinforced fabrics though (not counting a tiny patch of CY soaked polyester on a RC plane), and I bet a lot of others haven't either. Plywood is a familiar, comfortable material whose properties are well understood. The real question is how, say 1/8" ply over EPS or urethane or balsa would perform in terms of stiffness, weight, durability, etc.

I think bamboo is a fantastic material. How would you say it performs in terms of stiffness, weight, durability, etc?

There's an eye opener.

Allen's right; that's for the whole bike. Here's a picture I took of a Renovo bike hanging from a scale at NAHBS.

I'm a ham fisted hobbyest builder. So far my bikes have been heavy, and flexy. They ride amazingly smoothly, and the flex most likely has a lot to do with that. In my opinion there is no finer material than steel for a bike frame. You can build a fine bike out of wood that will last you for years, but wood is a softer material than steel and therefore more susceptible to damage. My day to day commuter is a good ol' steel frame and the bikes I enjoy building for myself are smooth riding wood.

I spent some more time on Renovo's website, and I'm convinced. Now I wanna build one (not going to happen anytime soon, but I'll keep this mental excersise going). I could see two ways of going about it w/o using CNC.

The first method would be to carve the outside shape and then drill holes in it and insert hardwood dowels to use as thickness guides when carving out the inside, just like they do with dug out canoes.

The second method would be to stack together the basic shape from plywood or veneer in a stair step manner, then simply sand down the steps to the right shape (you could leave the steps on the hollow inside since they wouldn't be seen, but it would make the bike heavier).

According to Renovo's website, some woods wouldn't even require metal inserts at the head tube and BB (though probably still at the seat clamp), but it would be easy enough to bond in inserts cut from a throw away steel frame.

I would think all bonding and finishing should be done with a marine grade epoxy.