# Will glue do for this build?



## videoword (Feb 27, 2018)

I'm building one of these zig-zag chairs: https://the189.com/wordpress/wp-con...hair-Designed-by-Gerrit-Thomas-Rietveld-3.jpg out of Peruvian Walnut and my question is simply this: 

Will glue hold the weight of a person sitting or do I need to bolt it up like this earlier model from the 30s?:

http://www.moma.org/media/W1siZiIsI...B4MjAwMFx1MDAzZSJdXQ.jpg?sha=cd1b04289829e92f

I, of course, have been watching video after video showing how 'glue is stronger than hardware', but I wanted to get the opinions of some seasoned folks.


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## 35015 (Nov 24, 2012)

Yes...most likely.

However, the issue is, glued joints without joinery tend to fail catastrophically and that is not good. Jointed and glued unions tend to only "creep open" and not fail catastrophically. 

Good luck...It is an interesting design!


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## mmwood_1 (Oct 24, 2007)

It would be interesting to experiment with. I think the question will probably revolve on whether or not those triangular cleats are sufficient to counteract the torque applied when sitting on it. The mating surfaces of the cleats against the main structures being the primary glue joints. One modification you could think about is doing finger joints instead of just butt joints for the miters. But maybe that wouldn't be needed. Please let us know the results when you do it. I would definitely be interested to know.


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## Steve Neul (Sep 2, 2011)

I wouldn't sit in it. The glue surface area is too small to support a person for any lengthy use. If the corner blocks on the inside was bigger it would function however it would detract from the design. What the chair actually needs is a welded metal frame and then veneered over to make it look like wood.


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## videoword (Feb 27, 2018)

Thanks for the responses, they seem to reflect my own inner monologue.



Jay C. White Cloud said:


> However, the issue is, glued joints without joinery tend to fail catastrophically and that is not good. Jointed and glued unions tend to only "creep open" and not fail catastrophically.


Catastrophic failure on this chair would be especially bad, might need to install a parachute in the backrest. I'm trying to think of joins that would be both hidden and also improve the performance, but I'm having a tough time.

Possibly a tongue in groove along the edge there? That would be exceedingly difficult to achieve with my tools, but not impossible. 

Or maybe dowels on the inside of the angle? Only thing is the stress is pulling the joint apart, so I'm not sure that that actually adds any reinforcement?



mmwood_1 said:


> I think the question will probably revolve on whether or not those triangular cleats are sufficient to counteract the torque applied when sitting on it. One modification you could think about is doing finger joints instead of just butt joints for the miters. But maybe that wouldn't be needed.


I'm sort of curious about using a triangle as in example #1 from OP versus using a straight support as in example #2. The triangle is more difficult and I guess adds more surface area to mitigate the stress of pulling away. But the straight support piece... is really a lot simpler to make.



Steve Neul said:


> I wouldn't sit in it. The glue surface area is too small to support a person for any lengthy use. What the chair actually needs is a welded metal frame and then veneered over to make it look like wood.


Are you worried about the joint or the material breaking? Did you take a look at the second image joined with hardware? Would that ease your concerns?


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## Steve Neul (Sep 2, 2011)

videoword said:


> Thanks for the responses, they seem to reflect my own inner monologue.
> 
> 
> 
> ...


I wouldn't trust the joints. That is a lot of stress on a mitered joint, hardware or not. You could make something like that and sit in it a few times and not be a problem but over time wood stretches and would start pulling the joints apart. To me it's a novelty item to be looked at but not used.


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## 35015 (Nov 24, 2012)

videoword said:


> Catastrophic failure on this chair would be especially bad, might need to install a parachute in the backrest. I'm trying to think of joins that would be both hidden and also improve the performance, but I'm having a tough time.
> 
> Possibly a tongue in groove along the edge there? That would be exceedingly difficult to achieve with my tools, but not impossible.
> 
> Or maybe dowels on the inside of the angle? Only thing is the stress is pulling the joint apart, so I'm not sure that that actually adds any reinforcement?


As this is a modern design in general, I would probably move a little way out of my day to day traditional methods to fulfill a clients wants for such a chair set.

This could (if tools are limited) be carried out very easily with a limited set of hand tools depending on the final desired effect in the design. What tools and experience do you have with them?

I would probably not use dowels but a toggle free tenon as produced by the Domino 700 by Festool...or its equivalent made by hand, then mortise and tenon the joint...if...I when that route.

Before I got to the "all joinery" method (more traditional) I may well explore with a client there interest in textile lamination systems germane to such designs. With an application method of something like Ecopoxy, and a textile joint system, failure at the joint area would almost be eliminated in my experience. Combine this with a traditional toggle free tenon and the loads required to achieve failure would exceed human capacity most likely...

I would note here these designs exist...and...NO, they don't fail, so speculation there is moot. Achieving such joint unions does take good design and expertise in execution...


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## woodnthings (Jan 24, 2009)

*Obviously, the system works ....*

What ever the system used to join the pieces works, but there probably is a "load limit" restriction on the weight of the occupant. The older version appears to have dowels or lag screws running back into the wedge piece:









My solution would be angled finger joints or dados filled with same width pieces and glued. The end or edge glue surface area is not sufficient in my opinion to carry the tension loads. Using the dados and small pieces will create more face or long grain glue area, for a better bond:


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## videoword (Feb 27, 2018)

Jay C. White Cloud said:


> With an application method of something like Ecopoxy, and a textile joint system


I'm having a hard time getting any information from google when I search "Textile joint system". Do you have a link that could enlighten me?


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## 35015 (Nov 24, 2012)

videoword said:


> I'm having a hard time getting any information from google when I search "Textile joint system". Do you have a link that could enlighten me?



Hi VW,

I must admit I am getting into some thin ice on this one...

Much of the world of "sewn joinery," "cloth lamination" and related are proprietary to those doing the work. Few of us share with each other, and I have to protect their patent pending status. 

My own currently are all proprietary as well to my work in upholstery and related project that involved all natural materials, sinew, leather, natural fiber, etc.)

Below should give some inspiration...I hope! let me know.

Hemp Cloth

Also done with bamboo cloth as well...

Natural Cloth Resin Joints

This method below in all wood and glue may also stimulate some ideas for you...:grin:


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## Woodknack (May 12, 2017)

Wood Magazine built a cantilevered rocking chair that created quite a stir. They answered accusations that it had to be weak by posting video of it holding 3 grown men. So you might look it up and see if it provides any insight. But it would be easy to build a prototype of the Zig zag and test it out. I agree that for durability it needs more than just glued miters, box joints would be a good choice.

Edit, the original Zig zag used dovetails. 

https://www.woodmagazine.com/project-plans/furniture/seating/zigzag-rocker-downloadable-plan


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## videoword (Feb 27, 2018)

Woodknack said:


> Wood Magazine built a cantilevered rocking chair that created quite a stir. They answered accusations that it had to be weak by posting video of it holding 3 grown men. So you might look it up and see if it provides any insight.
> 
> Edit, the original Zig zag used dovetails.
> 
> https://www.woodmagazine.com/project-plans/furniture/seating/zigzag-rocker-downloadable-plan


Here is the Zigzag rocker video. Shows the joint and the weight it was able to hold: 




And then, autoplay took me to this video of the current chair by Cassina being built. With dowels! (A form of loose-tenon?)

Going to have to mull this over based on the tools I have (a hand drill, in this case): 




OR just bite the bullet and use hardware, think that could achieve the same ends.


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## Woodknack (May 12, 2017)

Give dowels a try. I'm curious how it turns out, hope you post updates.


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## videoword (Feb 27, 2018)

I'll certainly be posting updates! Thanks for the input (everyone), really got me headed in the right direction.


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## GeorgeC (Jul 30, 2008)

I would not sit in either the bolted or just glued chair. Of course I also weigh 240 pounds. (not all of it muscle)

The wood would have to be thicker for me to feel it is a safe design for all comers. If the chair is being limited in who can sit on it I would not use any metal fasteners.

The J, C. White Cloud chair is a totally different design using different principles for strength. I would have no qualms sitting in that chair.

George


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## 35015 (Nov 24, 2012)

GeorgeC said:


> I would not sit in either the bolted or just glued chair. Of course I also weigh 240 pounds. (not all of it muscle)
> 
> The wood would have to be thicker for me to feel it is a safe design for all comers. If the chair is being limited in who can sit on it I would not use any metal fasteners.
> 
> ...


I am one of those that really likes to be supportive of ideas that are well outside what I would design or do. As a teacher, it's part of the job to always be encouraging. I would also add, I'm not a big fan of "ultra modern"...(aka the Jetsons) design styles, but that's just me being old fashioned.

So, I diffentiently want the OP to follow his own interest and feelings in pursuing this design. That is what will make it his...

*Nevertheless, GeorgeC. has raised a critical and very valid point in..."Good Design"...system and..."Best Practice."
*
Your design..."has to be"...safe for the worst case scenario!!!

I liked the video, but the fact that the chair failed the way *it did (catastrophically!!!!!)* suggest that even though it may score high in the "cool and modern" scale, it fail horridly in the "bomb proof" design area.

Bolts or Pegs...neither are going to change this design from failing in a very bad way if overloaded, stress by age, or sat in by someone that shouldn't...

It does need to be re-designed to accommodate only failing (if it did) in such a way that the occupant does not take a fall like in the video.

To be encouraging, I still believe it can be done with an application of one of the systems I mentioned already adapted to this design.


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## woodnthings (Jan 24, 2009)

*I had a different opinion*

After watching the video of the single rocking chair support being test to 420 lbs of weight, at twice the the lever arm length, I thought it did remarkably well, not a "catastrophic" failure. Also as an Idustrial Design teacher, we always tested our student's chair builds to failure point to insure they were safe. We even reduced the number of support and structural members to a point to encourage failure. This we called minimialized testing. When the device failed, we knew that was "one too many" members removed and that mamber was either critical in the design or worked in conjunction with others for structure. Without sophisticated testing devices, like a Consumers or Bell labs it's difficult for a school project to be tested fully.

Mathias Wandell ran some very interesting tests on the amount of glue used:






He also tested wood joint types, dovetail VS box joints:






The tests are as sophisticated as a home shop could be, in my opinion, and no humans were endangered in the process. The results were surprising in the joint test with a "gapped" jointed having more strength than the others.... :|
https://youtu.be/14Mkc63EpMQ?t=294


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## Tool Agnostic (Aug 13, 2017)

I am a newbie woodworker with limited experience, so these may be a dumb ideas. They may also violate the artistic integrity of the piece, so take it for what it is:

1. I wonder whether an alternative design might use a larger triangular support piece for possible added strength, but cut it shorter to hide it, so that it does not extend all the way out to the sides. I don't know whether the size vs. length tradeoff adds strength or not. 

2. I wonder how the grain orientation of the triangular piece might affect the strength of the chair. You might want to arrange it for maximum support strength. I presume that if you arrange it so that the grain goes up and down, it could provide greater compression resistance. What about making a laminate of stacked triangles with alternating grain direction. Would that be stronger?

That's as far as my thinking goes. Take it for what it is worth.


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## Woodknack (May 12, 2017)

Jay C. White Cloud said:


> Your design..."has to be"...safe for the worst case scenario!!!
> 
> I liked the video, but the fact that the chair failed the way *it did (catastrophically!!!!!)* suggest that even though it may score high in the "cool and modern" scale, it fail horridly in the "bomb proof" design area.


The Wood Magazine test leg had a longer seat, meaning significantly more leverage on a much narrower joint (miter with 2 splines) and it held 2 men until they started bouncing. The zig zag stool by comparison has a much wider joint and short seat which means significantly less mechanical advantage.


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## 35015 (Nov 24, 2012)

woodnthings said:


> After watching the video of the single rocking chair support being test to 420 lbs of weight, at twice the the lever arm length, I thought it did remarkably well, not a "catastrophic" failure.


I like the videos you just shared...

I do wonder if they can reflect actual comparatives to a true mortise and tenon joint? They seem to only reflect the bond tension of a surface to surface interaction. I'm not sure one could extrapolate true comparative correlation to any actual various forms of mortise and tenon glue methods? At least none I have seen both in furniture (with glue) and in timber framing without adhesive.

I felt (just my perspective) that the failure in the video of the rocking chair joint and folks falling on their collective backsides would warrant the perspective of "catastrophic failure" but that's just me.

I think the design, overall, would probably be "strong enough" yet I would not recommend it myself as a production run system to follow for a Rocker, accept for perhaps one done as an artistic expression in design.


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## Toolman50 (Mar 22, 2015)

videoword said:


> I'm building one of these zig-zag chairs: https://the189.com/wordpress/wp-con...hair-Designed-by-Gerrit-Thomas-Rietveld-3.jpg out of Peruvian Walnut and my question is simply this:
> 
> Will glue hold the weight of a person sitting or do I need to bolt it up like this earlier model from the 30s?:
> 
> ...


I think that will become a chair you have to monitor to prevent an embarrassment. 
Oh no Aunt Ethel, don’t sit there, you’ll be more comfortable over here. >


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## woodnthings (Jan 24, 2009)

*I thought of a different way .....*

Thinking about my previous post with angled dados with same width "splines" idea, I came up with this. Make a plywood gluing form with the correct seat, back and floor angles having open spaces from rails running lengthwise, rather than a solid seat like supports. Have stop blocks for your basic dimension, so when you make your glue up laminations they are the correct distances apart. Start laminating 1" X 3/4" strips in the shape of the chair, overlapping them on the ends as you go. Some strip will need the correct angles precut on them. These will get trimmed off after it's all done. Continue to build across the width with the strips attaching them to the previous ones which have set up. You can make it as wide as need this way and the alternating strips will form their own finger joints without having to cut individual dados. It will still look like angled finger joints, but made with individual strips.

It will look much like this:


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## Woodknack (May 12, 2017)

I showed the Zig zag chair to my wife and to my surprise she loved it and wants one in teak or walnut. So of course I agreed. To be honest I think the form looks silly but it is interesting from an engineering and design standpoint and obviously gets a rise out of people.

I legit like the Zig zag rocking chair, beautiful design and engineering, and might build one for the deck.


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## videoword (Feb 27, 2018)

woodnthings said:


> It will still look like angled finger joints, but made with individual strips.


Oh! I see what you mean and that would be cool. Totally different approach, but a really great idea and in some ways very easy to manage with minimal tools. I already bought my wood boards, so I probably won't go this route exactly, but since I am building my 15in width out of three 5in boards, I could at least do the interlocking between each board - even for the angles. I'll have to ponder it.



Toolman50 said:


> I think that will become a chair you have to monitor to prevent an embarrassment.
> Oh no Aunt Ethel, don’t sit there, you’ll be more comfortable over here. >


Too funny and too true. Aunt Ethel probably had it coming.



Woodknack said:


> I showed the Zig zag chair to my wife and to my surprise she loved it and wants one in teak or walnut. So of course I agreed. To be honest I think the form looks silly but it is interesting from an engineering and design standpoint and obviously gets a rise out of people.


Ha! So you are going to build the chair rather than the rocker? The form is, I think, supposed to look somewhat silly (or maybe light-hearted is a more historically accurate description). Reitveld made it in an attempt to design the simplest chair possible - out of a single board. The surprising simplicity of the zig zag design he ultimately discovered led him to describe the piece not as a chair but as a "designer joke". Joke or no, I find it is really stunning.


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## 35015 (Nov 24, 2012)

*More Info...*

Hi Videoword,

When you started this thread I pulled out some old info on these...and just got around to compiling some stuff that may be of interest...Good Luck with your project. Link is below.

Zig-Zag Chair


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## videoword (Feb 27, 2018)

Thanks for compiling those. I also went to down a showroom that resells the officially produced chairs and took some measurements. It's a little different than the pictures seem to indicate on first glance. Each plane is tapered slightly, creating something of an optical illusion. I'll post some pictures of the progress in the projects showroom.


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## 35015 (Nov 24, 2012)

videoword said:


> Thanks for compiling those. I also went to down a showroom that resells the officially produced chairs and took some measurements. It's a little different than the pictures seem to indicate on first glance. Each plane is tapered slightly, creating something of an optical illusion. I'll post some pictures of the progress in the projects showroom.


Awesome...I saw a very similar one over the weekend myself in a boutique...Springy but much stronger than expected. I actually like the design a lot now that I have seen something up close! Modern does have its place and these simplistic designs are compelling in nature and stature. The whimsy of them is kind'a cool...

j


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## Woodknack (May 12, 2017)

Any build progress?


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## videoword (Feb 27, 2018)

Woodknack said:


> Any build progress?


Slow, but steady: 

http://www.woodworkingtalk.com/f13/zig-zag-chair-progress-197282/

:smile2:


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