Will glue do for this build? - Woodworking Talk - Woodworkers Forum
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post #1 of 29 Old 02-27-2018, 12:48 AM Thread Starter
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Will glue do for this build?

I'm building one of these zig-zag chairs: https://the189.com/wordpress/wp-cont...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/W1siZiIsIj...1b04289829e92f

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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post #2 of 29 Old 02-27-2018, 01:28 AM
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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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post #3 of 29 Old 02-27-2018, 01:58 AM
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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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post #4 of 29 Old 02-27-2018, 08:26 AM
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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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post #5 of 29 Old 02-27-2018, 12:00 PM Thread Starter
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Thanks for the responses, they seem to reflect my own inner monologue.

Quote:
Originally Posted by Jay C. White Cloud View Post
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?

Quote:
Originally Posted by mmwood_1 View Post
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.

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Originally Posted by Steve Neul View Post
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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post #6 of 29 Old 02-27-2018, 12:13 PM
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Quote:
Originally Posted by videoword View Post
Thanks for the responses, they seem to reflect my own inner monologue.



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?



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.



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?
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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post #7 of 29 Old 02-27-2018, 12:13 PM
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Quote:
Originally Posted by videoword View Post
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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post #8 of 29 Old 02-27-2018, 12:30 PM
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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:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

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post #9 of 29 Old 02-27-2018, 12:39 PM Thread Starter
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Quote:
Originally Posted by Jay C. White Cloud View Post
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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post #10 of 29 Old 02-27-2018, 01:22 PM
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Quote:
Originally Posted by videoword View Post
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...

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post #11 of 29 Old 02-27-2018, 01:37 PM
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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...nloadable-plan
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post #12 of 29 Old 02-27-2018, 07:09 PM Thread Starter
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Quote:
Originally Posted by Woodknack View Post
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...nloadable-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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post #13 of 29 Old 02-27-2018, 08:18 PM
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Give dowels a try. I'm curious how it turns out, hope you post updates.
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post #14 of 29 Old 02-27-2018, 09:29 PM Thread Starter
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I'll certainly be posting updates! Thanks for the input (everyone), really got me headed in the right direction.
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post #15 of 29 Old 02-28-2018, 06:23 AM
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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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post #16 of 29 Old 02-28-2018, 08:33 AM
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Quote:
Originally Posted by GeorgeC View Post
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
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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post #17 of 29 Old 02-28-2018, 10:25 AM
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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

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

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post #18 of 29 Old 02-28-2018, 02:16 PM
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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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post #19 of 29 Old 02-28-2018, 02:29 PM
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Quote:
Originally Posted by Jay C. White Cloud View Post
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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post #20 of 29 Old 02-28-2018, 05:08 PM
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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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