I made a new joint

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On 5/19/2009 5:46 AM RicodJour spake thus:

What do you mean? It should fit tight as a drum.
It is a bit of a puzzle, so maybe you just need to visualize how it comes together. (Took me a while, and I'm the one who dreamt it up.)
There is some waste, sure, since the legs are narrower than the center of the joint, but that happens many places in woodworking. We love to waste wood!
--
Found--the gene that causes belief in genetic determinism

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I did visualize it, and I visualized a problem. You have tight joints, all square corners and edges, the first two pieces slide together, what happens with the third? It has to be twisted into place, and if you have exact cuts and square edges, where's the leeway to assemble it? You could undercut the joints so only the top edge is tight, but that presents other problems.

The waste is not an issue in my mind if the joint goes together. If the joint doesn't go together and fit tightly, well, then you get 100% waste!
R
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I don't see the problem here, as long as the portions of the "hub" that do not have a "spoke" adjoining it are at least 60 degrees (i.e., at least as big as the spokes). If the spokes are wider than that, the last piece won't slide in.
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On Tue, 19 May 2009 11:21:03 -0700 (PDT), RicodJour

I believe the 3rd piece would have clearance to slide into place along the axis of the member. I believe I see the problem you're referencing, and it would surely prevent assembling a similar 4-member joint. But 3 pieces with an angular separation of 120 should slide together quite well.
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Depends on the relative size of the circle. The drawing is not real clear for visualizing that, but make the bulges very slight, so the circle is barely bigger than the hexagon where the (extended) legs intersect, and it won't work. Make the circle very large relative to the legs and it obviously works.
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You are absolutely correct! As long as the radius of the central circle is greater than the width of the leg (diameter = 2 x leg width) it will assemble OK. But as soon as the radius is less than the leg width, it will begin to see interferences trying to slide that last member into position.
Numerical example: For a leg width of 1", a central circle greater than 2" diameter will allow assembly. A central circle smaller than 2" diameter, i.e. 1.5 inch diameter, will cause interference trying to insert the third leg.
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On 5/19/2009 11:07 AM David Nebenzahl spake thus:

Dang. Now I'm gonna have to actually make this sucker to see if it can be assembled without resorting to hammers and such.
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I think that is structurally the same as your first joint, The shapes of the lapped pieces are different, but otherwise it is the same joint.
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On 5/18/2009 2:06 AM Morris Dovey spake thus:

My bad; I probably should have been clearer.
The joint is shown correctly, and the finished joint as well. But what I left out is that the joint will have voids on the sides. (This is what I meant by the "puzzle" part of this joint; I still haven't figured out how to lay it out to minimize the waste, or to maximize the width.)
The original joint doesn't have this flaw, but then it's a lot harder to make. (Unless, of course, you set up your CNC machine to cut it. But even then you'll have to finish the sharp corners by hand.)
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David Nebenzahl wrote:

Clarity is good - or so I was telling myself at 4am :)

Actually, you did a such a great job with the original that I'm not very concerned with the second (but put me on your mailing list for when you make the second work without voids!).
I /will/ eventually CNC cut the original - and won't need to finish the sharp corners by hand. The top three photos at
http://www.iedu.com/DeSoto/Projects/Bevel /
illustrate CNC routing done with a 1/32" (0.79375 mm) bit, which would leave a 1/64" radius at (only) the three inner points. If you didn't already know what to look for, they'd look sharp. I've seen 1/64" bits advertised, but why bother? :)
By the way, the photo at the bottom of that page shows a 1/4" tenon cut on the end of a 1/4" thick board - with a shoulder all the way around. :)
And to return the favor you've done me, I have a lap/scarf joint you might find interesting. It demonstrates a bit of what becomes possible with CNC cutting.
http://www.iedu.com/DeSoto/Projects/LLJ /
Finally (to get even with you for not telling me about those voids!), at
http://www.iedu.com/DeSoto/Projects/JBot /
there're photos of a DIY CNC router with a 1/4800" step size intended just for joinery operations - and I think you might have a lot of fun with something like. Best off all, it took less than a half-sheet of 3/4" Baltic birch...
--
Morris Dovey
DeSoto Solar
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