That is a fabulous idea, and one which I tried on the red box. Which is why if you look closely you can see that the hinge areas are now splayed out at the bottom. 
When I heated it gently the hinges started moving a lot under the residual tension.
I would try it again, but not without fabricating a ring that fits over the bottom edge and keeps the hinges in line until they cool off.
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You are absolutely correct, it does indeed crack across the uncut areas. I don’t think the tape would add much structure though. I think the hinge is just on the edge of what the material can handle in terms of stress. I will give it a try next time though, there is really only one good way to find out!
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I have tried solid woods. So far the plywood has worked the best for a living hinge. Mahogany turned brittle. Haven’t tried walnut yet.
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My envy of the mighty jkopel grows.
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Of course, if you have a heat gun or lamp (or for wood, a little steam box), you could just eliminate the living-hinge part entirely. One of the things I definitely want to do with the glowforge is bending jigs.
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I just did a small box (3.25x3.5x1.75" tall) with living hinges using 1/8" Baltic Birch. But it looks like you’ve only got 5 “spikes” where I have 8 over an inch & a quarter along the length of the side piece. If you extend the hinge pattern a bit it will give it more relief and you should be good.
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Yes - played with this a lot. As best as I can tell, you can’t do a living hinge in solid wood (someone will no doubt prove me wrong). It needs plywood.
I don’t know of any plywood sold (other than Proofgrade) that guarantees a solid core - baltic birch is claimed to, but as you discovered, often doesn’t. I just recommend planning for breakage and making sure to test a lot before assembly & finishing.
Very early on, I did a large precision bend of a sheet of acrylic across a laser-cut former so I could get exactly the right radius. Was surprisingly easy and came out perfectly.
Great project, Josh!
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I ran through about 35 pieces of 12x20 from one supplier, and had no voids(that i found). I ran the very first piece of a stack of 75 12x20 that i got from a different lumberyard that ordered it in and it split due to voids. I’m guessing i was terribly unlucky.
I ran through 6 more pieces and had found only one more void, but it was inconsequential. Perhaps because i had just been affected by a void i was hyper sensitive to finding another.
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As a sometime woodworking type, I’d think that the problem for living hinges in solid wood is the way the grain works. There’s not a lot of tensile strength across the grain, so if you make your hinge that way you’ll just break the wood unless it’s very thin. And there’s a lot of stiffness along the grain, so if you make your hinge that way you’ll need zillions of closely-spaced cuts (and then you’re relying on cross-grain strength to transmit the load, which also tends to be a loser.)
A couple of suggestions that might work:
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Kerfing, which is the traditional way to make curves in soild wood when you don’t have bending equipment. You have to have the power/speed dialed in very accurately, because you’re making a whole bunch of cuts just short of through the wood. Each kerf cut gets you an angle that’s the width of the cut divided by the depth, so really you’d like to do super-deep engraving for this.
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Through cuts with interlocking fingers. There are a lot of finger-joint styles that are bigger at the ends so they don’t pull apart, and although usually the kerf would be a bad thing in this kind of joint, it will be good if you want some play that you can use to get the pieces to lock together out of plane. You could make a series of these joints and get any arbitrary angle. (Probably need to stabilize with a little glue or hardening finish afterwards, and definitely with tape during assembly) With the right joint pattern(s) that could be seriously decorative.
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So Kerfing sounds like a perfect application of a CNC…
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Yes. The only trick is not to break up the material between the cuts. In my limited experience with wood, a circular blade seems better at this, while a router bit tends more toward tearout. (It just occurred to me that with curved kerfs and judicious removal of excess material you can do some convex curves in 3 dimensions. That would be worth the problems of getting the routing/milling right.)
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Very cool! Thanks for sharing.
And I wonder how the Glowforge will do with a deep engrave for doing a kerf curve.
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I imagine thirty seconds in the microwave wrapped in a damp towel would help it bend as well?
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I am pretty sure that is birch plywood, but it is hard to tell from the instructable.
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It does kinda look as if it has surface layers and a core of different material, although that might conceivably be sanding and finishing.
This one says hardwood…
But I guess it just comes down to math and the torsional yield strength of the material used…
http://www.deferredprocrastination.co.uk/blog/2011/laser-cut-lattice-living-hinges/
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Hmm, that one that says hardwood lists padauk in the BOM, but the picture of it looks suspiciously like mdf!
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Yup, that is the same site I linked to in the original post, he has some great engineering math going on there. There seems to be a lot of flexibility in terms on various sites, and they play fast and loose with words like wood, hardwood, laminate, etc.
As @B_and_D_T says, that link definitely is not a picture of Padauk, which is an unmistakable bright orange.
The bottom line for me is that we are either going to have to do our own experiments and/or stick with @dan’s well tested proofgrade materials.
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