Solo Chair

Hmm, I'm thinking a wood/fiber/wood/fiber/wood layering (two layers of fiber around a wood core instead of one) would act somewhat more like an I beam construction.

I'm basing that on the failure mode of the piece you had with the single carbon fiber layer, and my research on wood bow construction. In your sample piece it looked like the wood failed in expansion mode on the down side (more or less as I'd expect), so if you had another fiber layer in there it should provide resistance to the expansion forces on the "down" side of the piece. Wood sustains pretty well under compression whereas fiber is pretty good at resisting expansion so they'd balance each other out pretty well. I think in that case the middle layer (or layers, could certainly be more than one strip of wood laminated in there) should be the thickest and the outer two wood layers close to veneer. This is also more or less how a lot of bows are built (whether fiberglass on wood or old school sinew on wood the ideas are the same).
 
I think putting the carbon fiber in the middle doesn't do much service.

If you expect it to bend one way, the carbon fiber is probably best in tension, so should be towards the convex side of the bend - like the rebar is always placed near the bottom of a driveway.

If you are not sure which direction the stress will come, I would put any wood (even balsa) n the center, then a layer of carbon fiber on both sides, covered by a show layer of pretty veneer. I bet it will hold your weight.

My demo of a torsion box is 5 mm plywood, 4 cm x 10 cm, 80 cm between supports, that supports my weight (200 pounds, 90+ kg). Basically it demonstrates that the strength of a beam in on the outside, with the only function of the material in the center to hold the outsides in position. Hence I beams have a thin web. Hollow core doors often have a cardboard core.
 
Well back to the drawing board, the wide narrow pieces I made are not working, even with the clamping jig, I cannot get the pieces to pull together enough to get a good glue up.
I'm going to get some more wood and try thinner strips, maybe only a few millimeters thick.
I've spent a few weeks doing this and to have this happen, well the CoC will not let me completely express my set of mind...
 
...I'm going to get some more wood and try thinner strips, maybe only a few millimeters thick...

I've had good results using laminations that are about 3/32" (~2mm) thick. What glue are you using? Titebond, etc., tends to creep, and seems a bit 'soft.' Powdered recorcinal glue allows more opwn/working time, and dries overnight to a very hard and strong joint, with no creep. Expensive and messy, there's always epoxy.
 
I've had good results using laminations that are about 3/32" (~2mm) thick. What glue are you using? Titebond, etc., tends to creep, and seems a bit 'soft.' Powdered recorcinal glue allows more opwn/working time, and dries overnight to a very hard and strong joint, with no creep. Expensive and messy, there's always epoxy.

I use the basic white glue, and for the carbon fiber epoxy, but that is not the problem. The problem is when I steam bend these 15cm (6") wide pieces they cup when they dry, the pieces are about 6-5mm (1/4"-3/16") thick What I'm going to try next is to cut them much thinner, and not steam bend them, or I have to cut them much thicker and steam bend them.
 
I haven't done enough bending to call myself an expert, but I start with very thin wood, and never use white or yellow glue since it creeps (my first choice is urea resin glue that I use for veneering). I have never done any steaming.

How thin does the wood have to be? Just enough that it doesn't break when bent, which depends on how severe a bend and how wide a board, but 4-5 mm would be a common starting point. I use a carbide blade in a big bandsaw, so the cut is smooth enough that I can get 4-6 "veneers" before a quick pass on the jointer to give me a new starting reference surface against the bandsaw fence. The urea resin glue is gap filling which gives forgiveness for the slight roughness of a bandsawed surface (in fact with shop cut veneers, I glue the sawn side to the substrate and sand the finished surface after the glue dries).
 
I haven't done enough bending to call myself an expert, but I start with very thin wood, and never use white or yellow glue since it creeps (my first choice is urea resin glue that I use for veneering). I have never done any steaming.

How thin does the wood have to be? Just enough that it doesn't break when bent, which depends on how severe a bend and how wide a board, but 4-5 mm would be a common starting point. I use a carbide blade in a big bandsaw, so the cut is smooth enough that I can get 4-6 "veneers" before a quick pass on the jointer to give me a new starting reference surface against the bandsaw fence. The urea resin glue is gap filling which gives forgiveness for the slight roughness of a bandsawed surface (in fact with shop cut veneers, I glue the sawn side to the substrate and sand the finished surface after the glue dries).

I'm going to cut up the stock tomorrow cut, plane cut, plane, so I have one side planed flat, then run down to my buddy Alex's place and use his sander!

I think I'll shoot for 3mm thick, or thin, LOL as I want to bend them cold.

Charlie do you mean that Gorilla glue stuff?

I don't know if I can get that here...?

Should do the trick, fingers crossed.
 
Vaughan has the right link, but it is often available from local stores around here. One pound will be more than enough. I use rubber rollers without a nap to apply it, about the thickness of latex paint, on one surface. Long open time. I use vacuum bags for most of my clamping, but regular clamps work fine. I mix in a plastic container like a sour cream or cottage cheese box, and leave any leftover in the mixing container. When it dries it pops out of the flexible plastic, but you can tell just how dry the work piece is by what is left in this test container. The roller and mixing tools wash clean with lots of dish soap and water.

I have a very low opinion of gorilla glue. If I need a polyurethane glue to attach non porous surfaces (like pre-finished work) I find PL Premium construction adhesive like this: http://amzn.to/2dziQKt available at the local construction stores (e.g. Home Depot). As with most poly glues, the nozzle dries and plugs, but then I punch a small hole in the side of the tube and use the rest of the tube a little at a time that way - the wound heals and I punch a new one next time.
 
OK I made my banzai run down to Alex's shop, it was great to catch up with him, it's been too long, got all the pieces sanded. I know what I'm getting myself for Christmas this year :D

I put enough of the 3.5mm strips into my bending form to see how they would bend, well they bend with ease.

I'm making a new bending form, the other one was adapted from a 7 degree bend and I just don't like it, it's sloppy.

Now I want a 10 degree bend, but I'm concerned about some rebound after it is glued up, so I was thinking (always dangerous) to make the form 11 degrees or even 12 degrees, anyone care to comment on that idea? :huh:

I think I've found the Urea glue here, but it is not cheap and takes 6-10 days to ship..... I can have two 1 pound buckets shipped from the US for about $10 more total than the stuff here and I'll have it by Wednesday. I know Charlie that you said a 1 pound would do, but I have a lot of strips, 11 for each leg, so that is 10 glue lines, glue on each side, each one is 100 cm long by 13 cm wide, so that is about 2.6 square meters of glue us times two so 5.2 plus alpha lets just say 6 square meters of glue up surface or 65 square feet. I found on their home page this "One pound adhesive powder plus water at .0006 inch glue line covers about 40 square feet", to be safe I'll be getting two 1 pound buckets.

Wish me luck, this job needs to be done, like last week.....
 
...I want a 10 degree bend, but I'm concerned about some rebound after it is glued up, so I was thinking (always dangerous) to make the form 11 degrees or even 12 degrees, anyone care to comment on that idea?...

With the urea glue, and the laminated joinery, you shouldn't have any rebound. The parts should come out of the forms intact, and as solid (or even more so) than a solid one piece part would be.
 
Are you sure the carbon fiber is going in the right direction for this task? Looks like you are creating the equivalent of a flitch beam with your present plan. This would resist a sideways bending of the leg. Don't you really want to resist a bending of the leg into or away from the angle?
leg-1.jpg

If that's the case, shouldn't the carbon fiber be laminated like this? Just a thought.
leg-2.jpg
 
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