A Real High-wire Act

Stuart Ablett

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Tokyo Japan
I'm starting the build of the acrobatic high wire chairs.
I went to my wood wholesaler today.
This is what ¥21,000 of Beech looks like.

ebf93dc3611a5d16091f9a4a63857ce4.jpg



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hey stu, beat me to it i was guessing it at 28 ft from the picture.. but way over there 5 dollars for beech probally isnt bad.. its around 3.0 here in my area for select and better grade.
 
hey stu, beat me to it i was guessing it at 28 ft from the picture.. but way over there 5 dollars for beech probally isnt bad.. its around 3.0 here in my area for select and better grade.

Pretty good guesstimation there Larry :D

I picked through the pile and got the best stuff, but there was no "Better" grade I could get, only a selection of thickness. I think this should be enough to do two chairs, but I can always buy more.

BTW here is the chair-like-object in question....


high_wire_chair.jpg
 
Thinking of the joints for these chairs.... :huh:

For the tops of the front legs where they join the skirts they are mortise and tenon, but I think a sliding dovetail would be stronger, like this....


sliding%20dovetail%20leg%202.gif



or even this.....


sliding_dovetail_leg.jpg



(without the square protuberance on top of the leg)


the stretchers lower down would be simple M&T joints, as well as the back legs too.


These chair take a lot of abuse, at the end of the act they are dropped onto the safety net which is a good 8' above the stage, and at intermission when the lights go out, the safety net is dropped very quickly to the stage, and the chair essentially falls 8' to the hard stage, it hits in whatever orientation it hits, so it takes a beating.


Using the M&T joints relies on the glue to hold the joint together, I'm thinking that a sliding dovetail on the front legs would be a better combo of glue and mechanical holding the joint together.


The regular M&T joints I'm thinking of using a wooden peg to pin each joint, this would also create a mechanical joint that even if the glue fails the joint should hold.


What do you think?


Cheers!
 
Could you drawbore the top and bottom stretcher? If the tenon is wide enough you could even double drawbore it. That might help with racking. The drawbore would give you a mechanical joint that would hold even if the glue fails. Might be a little quicker than the dovetails too.
 
I'm thinking your dovetails are too close together and that inside corner of the leg could splinter out when suffering the abuse you mentioned. The corner cross piece is a belt and suspenders approach. If you were to extend those ends nearer to the outer edge of he seat rails in a quasi half lap and then double pin it with glued in dowels, I think the leg would have to break before the joint would fail.
 
I tried a sliding dovetail in a corner like that once. I could feel it cracking as the aprons (or whatever you call the male part) wiggled. I did lots of glue, and survived, but have avoided dovetails in corners like that... think of the grain of the leg, and how easy it will be to split the sides of the pins.

I suggest a pinned mortise as a better choice, by my intuition.
 
I really appreciate the input people, thanks! :D

Both examples I show there the aprons are set in from the corner which makes the dovetail joints much closer together than they would be in my example. With the skirts flush to the outside of the chair legs the dovetails would have a LOT more space between them. I do understand that this may not work, and a drawbore mortice might end up being the best solution, but I want to explore the dovetail route first.

Cheers!
 
Had to think about this for a while, but I'm heading towards the mortise and tenon crowd. The reason being that with the tops of the legs "open" the dovetail offers more opportunity for lateral forces splitting the leg.. maybe... It seems to be a tradeoff between that and the reduced pullout risk and greater glue surface... It's possible the glue surface will win out.

Looking forward to see what happens anyway :)
 
Had to think about this for a while, but I'm heading towards the mortise and tenon crowd. The reason being that with the tops of the legs "open" the dovetail offers more opportunity for lateral forces splitting the leg.. maybe... It seems to be a tradeoff between that and the reduced pullout risk and greater glue surface... It's possible the glue surface will win out.

Looking forward to see what happens anyway :)

Yes but, the seat of the unit is part of the structure and will be about 1/2" thick, Beech wood as well, so I could certainly peg or dowel the seat into the top of the leg/aprons to make sure the tops of the legs cannot spilt.

Remember people this is NOT a chair, it is a chair-like piece of acrobatic equipment :D

Cheers!
 
2 questions.

1) What method did the original chairs use? I'd probably lean towards using the tried and true method.
2) What about doing a test? Mock up both joints and run a test on them to see what is stronger?
 
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