Construction problem.

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Hi Steve,

This chair which the guy on Cutting Edge Woodworker made looks to be constructionally similar to your (very nice, btw) design. He just used M6 threaded inserts set into the back, so the big heads should be absolutely fine. He also did a double taper so that the widest part of the back was at the joint. Anyway, you might glean something useful from the pdf.

Cheers,
Neil
 
Hi Neil,
Thank you, again :)

It has occurred to me that the rails underneath do ot need to be maple. They could be ply, and indeed, could be solid, right across. That way I could get 6 nuts in quite easily, they could be in line with the face of the back (no need to insert them at an angle to match the rails) and the strength of the rails won't be compromised, because it is the same in all directions.

Ooh I can feel a brainwave coming on.

Cheers
Steve
 
Eric from the colonies here...

how about this idea.

your two curvitational underseat rails that butt onto the curved back lamination, they are, I agreee where the majority of stress is gonna occur, so I'd draw upon the concept of the "clenched nail" or the wedged tenon, and suggest that you place a block between the two rails, perhaps substantial, as in 8.4 material, and temporarily attach the seat assembly to the back. Then, judiciously cut 3/8 x3/8 moritices through the back into the seat rails, perhaps add a few in a curvilinear orientation into the 8/4 block.

then, taper the top and bottom sides of the hole with a 3.8 chisel, perhaps to dovetail angles, ..yer getting set up for wedged tenons here.

You glue the block between the rails to the back, not clearly strong enuf, cause it would just lift off the top ply under stress, but every little bit helps.

You could always use dowels on the ends of this block to attach it to the side rails if you wanted, or just pocket screws.

anyway, you mill up some 3/8x3/8 stock and glue it into the side rails, trim it off just a tad longer than yer 12mm back thickness, and cut a horizontal slot for the wedge.

you put the back in place over the tenons you've created, clamp it up, slather some glue on some wedges and drive em home, creating captured dovetails. Not easily removed or fixed, unfortuanately.

Any stress would concievably be carried throughout the entire thickness of the back, as opposed to just off the front frace.

If the 8/4 block was dowelled into the side rails, and the same wedged tenons were used along it's length, you could likely even triple or quadruple the strenght of the jointery.

OTOH, you could just use wood screws and plugs and metal dowels to achieve the same strength

This is sheer conjecture on my part, it would be a simple task to do a mock up and test it to assess the strength.

I betcha that Rennie Mackintosh fella did the same with his chairs. That high back spells substantial leverage to me.

Eric
in Calgary
we is still just using saddles, eh!
 
Hi Eric, Thanks for your thoughts.

Well, all those who are still rivetted by all this, what do you think of this? I've moved the rails a bit further apart and filled in with a stack of birch ply. I can then get 4 bolts in perpendicular to the surface of the back:

Four%20bolts1%20(Small).jpg


and

Four%20bolts2%20(Small).jpg


At M8 (5/16" if you are over the Pond), I think a horse could kiddle on it.

BTW Had some bumf from BigHead today, inc a few samples. I think they would be great in the back as I wouldn't have to remove as much material (although then I would be relying on the weld to hold).

Cheers
Steve
 
interesting solution steve.

i quite liked the chair on the pdf, but note that he was using 13 plies
wonder how thick it came out at???

still worry about the flexing.

great drawings though
paul
 
I think you are in danger of forgetting just how strong modern glue is your bolted solution would work with out glue .
If i had the skill to design and build this chair i would as recommended build a 'tester' glue and screws (original design + block) laminate a back following scrits recommendations and abuse it, not compromising the design is worth the experiment and if the back needs to be stiffer then finding a material to incorporate will be a interesting exercise.
 
engineer one":39bftwf5 said:
I quite liked the chair on the pdf, but note that he was using 13 plies - wonder how thick it came out at???
Assuming standard laminating veneers at 1.0mm +/- 0.3mm and 0.2 to 0.3mm glue line, probably around 18 to 20mm thick.

Steve Maskery":39bftwf5 said:
BTW Had some bumf from BigHead today, inc a few samples. I think they would be great in the back as I wouldn't have to remove as much material (although then I would be relying on the weld to hold).
Bighead will actually give you some leading factors for their stuff if you ask. I'd say that the wood to Bighead bond would probably fail before the weld, though, and I'm assuming an epoxy bond

Scrit
 
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