Tight Wire Chairs

Stuart Ablett

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Tokyo Japan
OK here we go, I've started the build of two tight wire chairs.


The chair makes it's appearance at about the 1:31 mark.

tight_wire_performers_1.jpg


A picture of the chair in use.

tightwire_chair_drawing_1.jpg


here is a line drawing of it.

From the source, here is what they have to say about the wear and tear of the chairs.

In the show, after the chair is dropped from the Highwire, it bounces in the net; this does not hurt the chair.
After the net is released, depending on how fast is comes down, it hits the stage at different angles every night.
The damage is inconsistent and unpredictable so we want the whole chair to be built with strength in mind.

The drop to the stage is about 2 meters, or just over 6 feet, twice a day, so building for strength is paramount.

The design is all fairly straightforward, with the exception of the rear leg.

To make that rear leg in one piece I think is a mistake, it will just snap. It splays out to the side and out to the back.

I have the idea of making it out of several thin pieces of wood, and bending the rearward splay into the lamination, while leaving the width of the lamination wide enough to cut the sideways splay on the bandsaw, if that makes sense.

I'd love to hear some ideas if you have them :D

The front leg is most likely to fail, look at this picture....

tightwire_chair_1.jpg


The close up is of the side of the front leg.

tightwire_chair_2.jpg


How to make these corners stronger. I think that they are just simple Mortise and tenon, but know one knows for sure, as the paint is rather thick, but I've been toying with the idea of doing a sliding dovetail to make the joint stronger, but maybe that is not a good idea, and I should just go with mortise and tenon and then pin them as I did with the Chinese chairs....?

The wood is beech, it is strong and works well, and as it is paint grade the simple grain does not matter.

The chairs are reinforced with metal brackets and such, which I'll also be making, more on that later.

Not nearly the volume of the Chinese Chairs, but they are certainly more complex.

I'd certainly like you input on these.

Cheers!
 
I think you have the absolute right idea with bent lamination's i am always reminded when it comes to something like you asking about of the Danish furniture industry. Chairs like this

no31.jpg


When you consider they take the full weight of a person on that single front leg.


Perhaps several bent laminations assembled together.

And for the wood i would look at using european beech as they do in plane bodys etc. Its a nice dense wood and stable and straight grain which should not present too many issues in laminating.

beech_european.jpg


This is the grain of the beech type I am thinking off. Its tough stuff have a small slab in my shop. Type of stuff used in those coffin planes made by Mathieson and used for many other woodworking tools through the ages. Stands up well to wear and tear and holds its shape.

Looking forward to watching this adventure.

Whats the news on the previous batch of chairs ? Have they been used and tested yet ? Customer delighted ......I take that for granted by the effort you went to.

Best of luck.
 
I think you have the absolute right idea with bent lamination's i am always reminded when it comes to something like you asking about of the Danish furniture industry. Chairs like this

no31.jpg


When you consider they take the full weight of a person on that single front leg.


Perhaps several bent laminations assembled together.

And for the wood i would look at using european beech as they do in plane bodys etc. Its a nice dense wood and stable and straight grain which should not present too many issues in laminating.

beech_european.jpg


This is the grain of the beech type I am thinking off. Its tough stuff have a small slab in my shop. Type of stuff used in those coffin planes made by Mathieson and used for many other woodworking tools through the ages. Stands up well to wear and tear and holds its shape.

Looking forward to watching this adventure.

Whats the news on the previous batch of chairs ? Have they been used and tested yet ? Customer delighted ......I take that for granted by the effort you went to.

Best of luck.

Yes Rob, European Beech is the wood to be used. I think making a basic caul that will allow me to glue up a bent lamination for the backwards splay, and then bandsawing out the sideways splay will work well.

The other chairs have arrived and so far everyone is pleased, they now have to be fit together into a stack, then finished and then fit together again. I've been promised pictures along the way.

Cheers!
 
The line drawing shows metal reinforcements at the bottom of the legs and across the stretchers. A 3-way metal brace at the top of the legs would strengthen whatever joint you use for the wood.
 
Well this will be interesting, some engineering challenges for sure :lurk:

I think your bent lamination theory is spot on. I'm not sure how bad the current design is but your improvement would certainly be better (under the "better to over engineer theory).

The vertical stress crack you're showing on the front leg is certainly interesting. I think that that joint is to sharp to do a reasonable bent lam there... I suspect a dovetail won't help much because of the failure mode (the rail isn't pulling out the leg is failing). I almost wonder if a metal strap running from the front of the leg up over the top onto the stretcher or maybe a tension rod run through the stretcher providing tension front<->back might be a solution...
 
Thanks guys.

Ryan, how about something like this....?

Front_Leg_Insert.jpg


Obviously not to scale etc, but you get the idea, the aprons are still mortise and tenoned into the top of the leg, and then a thin, 3mm thick piece of steel is let into the top of the leg and the tops of each apron for each front leg, screwed and epoxied into place it should not move. Of course the underside of each apron would still get the brackets like on the old chair.
 
Ryan, how about something like this....?

Something kind of like that yeah... I'm not a structural engineer and am struggling more than a bit to imagine the vectors on all the forces involved so take what I'm saying here for what that's worth (and I'm thinking out loud a wee bit here so play along and correct where it seems way off base, please :D).

What I think is happening on the front leg is the bottom corner of the leg[1] is impacting causing the chair to flex diagonally (direction indicated by arrows[2]) causing the joint at [3] to be flexed out at the end (3 isn't quite right but I think conveys the rough theory) ([1,2,3] indicate my rough scribbles in the picture).

tightwire_chair_forces.jpg

Obviously the same thing should be happening to the rear leg. What I believe is saving it in that case is that there is sufficient material above the joint to prevent it from splitting (the forces ought to be about the same and we see the same indication of impact points on the corners of the legs).

I think the crack there implies that the whole chair is flexing somewhat (you might be able to see evidence of this in the stretchers if there are compression points on the ends of them, maybe not though... depending on where it flexed). Its possible that the bottom rung is actually flexing up in the middle a bit I think that means that you might also be able to mitigate the issue somewhat by proper construction of those and maybe its all a moot point.

I was thinking if there was tension all the way to the front of the leg it would help mitigate the flex as well, but I'm not sure on the best way to do that. Your idea certainly seems like a reasonable one to try.
 
Basically I agree with your assessment Ryan.

I don't know if I'll do the let in bracket, but I am now thinking of making the front leg out of a laminated piece too, and even including fiberglass cloth in between each piece of laminated wood.

Should never split if I do that.
 
Stu if u got fibre glass cloth in mind then thinking of strip canoe building, any reason you could not use a bit on those joints and corners with something like system west epoxy.
Of course budget in both time and material come into play, but maybe this would be an opener to a conversation with client.
Just considering how strong a strip canoe shell is by comparison to thickness of strips and then how light the build would be. Lots of work but the chairs would last and for sure be safe. The fibreglass would not be visible in end product.

Sent from my SGH-I337M using Tapatalk
 
Stu if u got fibre glass cloth in mind then thinking of strip canoe building, any reason you could not use a bit on those joints and corners with something like system west epoxy.
Of course budget in both time and material come into play, but maybe this would be an opener to a conversation with client.
Just considering how strong a strip canoe shell is by comparison to thickness of strips and then how light the build would be. Lots of work but the chairs would last and for sure be safe. The fibreglass would not be visible in end product.

Sent from my SGH-I337M using Tapatalk

yes I'd like to do just about exactly that Rob, and we have talked about it, I'm trying to reduce the steel and screws and go for fiberglass cloth instead, but there are weight issues, they want the chairs to be the same weight at the existing chairs, as the artists are used to them.

Cheers!
 
Looks to me like u been hard at it. There is a fair bit of work in that form.
Following along with great interest. Thanks for keeping us abreast on progress.

Sent from my SGH-I337M using Tapatalk
 
OK it has almost been a month since I last updated this thread, so sue me :D

I've been banging my head against the wall here, nothing works the angles and measurements on their drawings are WRONG, not by much, just 'that much' but wrong.... :doh:

I cannot really blame them, they are taking measurements from existing chairs that have several coats of paint on them and are all beat up, really it was my fault for trusting someone else's measurements.

OK what to do now, well, basically I had to reverse engineer the chairs from the partial info I have.
For example no size or angles are given for the aprons on the chair, they are just left off the parts list. :eek:

What I can confirm is the footprint of the chair, the height from the ground to the seat, and the dimensions of the seat, I cut two pieces of 9mm thick MDF to the size of the footprint and the size of the seat, I then cut four boards to the height of the seat, then I started to take measurements, and figure out the angles. They did give me the side and rear kick back or kick out, so I could figure out where the seat needed to be in relation to the footprint.

mock_up_just_legs.JPG

The front legs are cut on each end with a compound miter of 3° front to back and side to side, the rear legs are cut with a compound miter of 7° back and 3° to the side, of course the right and the left legs are not the same (another thing not shown on the drawings). With the legs figured out, I could then move on the the aprons, and stringers.

mock_up_front.JPG


I'll admit right here that it took me TOO LONG to get my head around all of these angles, but I did, and now that the parts are mocked up, I can start figuring out the joints, which will be all mortise and tenon.

3degree_tenon.JPG

That may not look like much but for me it was a major achievement LOL :eek: a 3° angled tenon. I thought that I would have to make some compound angled tenons, but I don't think* I will need them.

Now the wood for this whole chair is too darn skinny, at only 38mm square it is really hard to make a solid chair, I've been back and forth on this and they don't want to change the chair's dimensions at all.

12mm_tenon.JPG

12mm thick tenon, too thick I think.

8mm_tenon.JPG

8mm that looks too thin...

10mm_tenon.JPG

Maybe 10mm is the Goldilocks size I need?

Next up I'm going to build all the parts out of 2x4s (what I'm using now, that is NOT Beech) and put it all together, then when I'm sure it works, I'll make all the parts in Beech.

This has really taken too long, but there has been a lot of backtracking, and working from a poor starting point, which I can only blame myself for.

Cheers!


*but who knows, ask me in a week :)
 
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Good to see you're making progress, Stu. :thumb: I'm guessing it's not workable for them to get a chair to you so you can take your own measurements?
 
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