How they do that?

[William Lai]

I have always been fascinated by this chair by Gerrit Rietveld, a design he produced from the 1930's. It's still being manufactured today, at least reproductions of it.

As far as I can research, the chair does use mechanical fastener, though I'm not exactly clear on the method. Here's one description that I found:

"This remarkably stark design consists of only four rectangular sections. The seat and back have been dovetailed together, and the seat and base reinforced with two triangular wedges. The brass nuts and bolts holding these wedges together represent one of the few times in De Stijl design where the hardware became part of the overall decoration. This system of joining belies the complex construction of the piece: the nuts and bolts must pass through each of the panels to produce the necessary strength for the cantilevered structure. "

Regardless, I wonder with the advent of modern adhesive, is there a way to build this without mechanical fastener? Perhaps with some sort of box joint technique, there'll be enough long grain contact for the adhesive to hold?

[Jeff Sudmeier]

Would you be able to trust glue for the long haul to hold those wedges? Without some type of mechanical connection, I would think that over time the glue would let loose and the joint would fail.

That said, that is a neat looking chair!

[Mark Singer]

William,

That is the Reitvelt Zig Zag chair...sometimes called the "Z" chair. The dovetail is a strong joint and doesn't require a very strong glue. This chair was part of the De Stijl movement...Mondrian, Van Doesburg and others. It is probably 1925 vintage and may have been used in the Schroder House in Utrech. It is probably a simple clair to make if you can make dovetails ...the angle makes them a little more challenging , but not much. The moment or torsion is taken by the wedges which were probably doweled...they could be biquited today.
If you are interested in making it , let me know and I will help with the details.

[Doug Shepard]

Dont get me wrong, but would you really want to sit in that chair? It justs to me like it would be very uncomfortable. No seat contour, no lumbar support, no back contour, etc. It would be neat to build as an exercise. I just wonder if I'd actually want to use it after putting the time and effort into it? Has anyone here actually sat in one? Are they more confortable than they look?

[Tom LaRussa]

Dont get me wrong, but would you really want to sit in that chair? It justs to me like it would be very uncomfortable. No seat contour, no lumbar support, no back contour, etc. It would be neat to build as an exercise. I just wonder if I'd actually want to use it after putting the time and effort into it? Has anyone here actually sat in one? Are they more confortable than they look?

If the "legs" flex, you're going to slide off the front.

If the seat flexes, the knife edge at its front is going to cut off the circulation in your lower legs.

If your floor isn't just about optically flat, the thing is going to wobble an awful lot.

But if you manage to stay on the thing, and it doesn't wobble too much, you will merely be very uncomfortable.

I'd be willing to bet money this thing won awards.

This is a perfect example of why those who want to design "for the sake of design" or "for art's sake" should stick to things that don't pretend to be something practical, like a piece of furniture.

This, of course, is just one Philistine's opinion.

BWDIK? YMMV. ETC.

[Mark Singer]

Tom,

I don't own this chair and this was not my thread....I may have sat in it a couple of times and it was surprisingly not too bad as I remeber. It is an important part of the the history and begginings of modern art and the International Style of architecture. The De Stijl movement was formed by a group of Dutch artists and architects and they created a forum much like SMC. The work of Mondrian was probably the best known art that emerged from this movement. The primary language was the use of geometric forms and primary colors. The Schroeder in Utrech is a jewel of the movement....it is as if it were a painting in 3 dimensions. This movement influcenced artists and architects throughtout the world. About the same time Chareau created the Maison de Vere, Corbisier The Villa Savoy, Mies , the Barcelona Pavillion, and Wright, the Textile Block homes, like the Ennis Brown and Storer house. The importance of the chair goes beyond its esthetics, it represnts an important movement. Just as our old chisels are really not important today we appreciate them and resist there replacement by newer , noisier power tools that are more efficient and maybe even more comfortable to use. The chair may have won awards , I don't know? Probably not for comfort...that would go to the Lazy Boy Recliner. It is a simple statement in the use of planes of wood to connect them in an elegant and simple way to form a chair.

I found a few images that represent the De Stijl movement...

This is the Retveld Chair on the cover...







http://images.google.com/images?q=tb...%2520Chair.jpg

[William Lai]

Tom: I agree with you and others that this is just not going to be a very comfortable or practical chair. I haven't sat on one, but all the points you raised are good points and mnay I hadn't considered before.

Nevertheless, I'm looking at it as a design and construction exercise, in which one needs to solve alot of structural problems for a piece that experiences alot of forces and stress. Usually these cantilevered designs are built using material like steel tubing, or one piece molded plastic (see below). Or I'm sure you've seen designs using bent wood as well. But this one is built from wood, and unlike the bent wood pieces, is totally reliant on the joints to handle the load, and so I find it pretty interesting and educational to think about as a beginning woodworker.

Besides, I wouldn't mind having one in the house; it's pretty neat looking! Though I'll probably put it to use as the chair where I can throw my clothes on, rather than sit on it

[Mark Singer]

Here is a link to the De Stijl movement....It is short and informative.


http://char.txa.cornell.edu/art/deca...l/decstijl.htm

[William Lai]

Thanks Mark for the info and link. The context of the chair is very interesting to me, and I particularly like your analogy of it back to the world of woodworking.

Regarding the joinery on the Z chair, can you elaborate on the wedge piece's structural function? I don't think I understand what you meant about it taking away the torsion of the chair. Focusing on the seat joint for the moment, it seems that the joint will want to rotate around the top corner of the wedge as weight is put on the chair, and while certainly having a larger connecton helps strengthen the joint, I am not sure how it changes the nature of the stress.

[Mark Singer]

William,

I have included a sketch that shows the forces on the chair. I have isolated a joint that shows the imporance of the wedge. The wedge is in compression as it resists the torsional force caused by the weight of a person. This then makes the dovetail function as a tension member. A good way to picture it is to picture 2 children on a "see - saw" as one goes up the other goes down. The fulcrum is in compression. The fulcrum acts as the wedge in the chair....the body weight, places the wedge in compression and the dovetail in tension. This is the strength of a dovetail joint. Without the wedge the dovetail would be in pure torsion and would fail. The load on the joint is calculated as the moment arm, aprox. 1 foot times the weight say 200 lbs. So the moment is 200 ft- lbs. The other joint has the same force. Since moments about a given point must equall zero...the resisting moment assumed acting at 3 inches from the end is 800 ft.-lbs. If the chair is 20 inches wide that means each inch must resist 40 ft-lbs. That means the tension on the joint is about 100 lbs per lineal inch.....Which means...You will need to make nice tight dovetails!

Thanks Mark for the info and link. The context of the chair is very interesting to me, and I particularly like your analogy of it back to the world of woodworking.

Regarding the joinery on the Z chair, can you elaborate on the wedge piece's structural function? I don't think I understand what you meant about it taking away the torsion of the chair. Focusing on the seat joint for the moment, it seems that the joint will want to rotate around the top corner of the wedge as weight is put on the chair, and while certainly having a larger connecton helps strengthen the joint, I am not sure how it changes the nature of the stress.

[Bob Hovde]

Mark,

The description in William's original posting says the back and seat are dovetailed, which means that dovetail joint is always resisting a rotational movement. It says the other joints are held together by brass bolts (rather than dovetails). Do you know something about the chair that wasn't in the description?

Bob

[Mark Singer]

Bob,

I am sure you are reading the thread correctly....I am not a good reader, my memory is more visual...The original was dovetailed ...I have a picture to prove it ....it is worth a thousand words...cause it would take that many to tell you the ones I saw were dovetailed....I am sure today there are other versions...my structural analysis would still stand....the resisting joint may have been revised..and different...they probably made it cheaper over time...like most things

Mark,

The description in William's original posting says the back and seat are dovetailed, which means that dovetail joint is always resisting a rotational movement. It says the other joints are held together by brass bolts (rather than dovetails). Do you know something about the chair that wasn't in the description?

Bob

[Mark Singer]

Bob, William,

I would guess if they are not using dovetails , It is most likely mortise and tenon with epoxy or another strong glue....If the tenon are on the seat porion they are in shear and bending ,that would be the stronger direction,

[Dave Richards]

If they aren't using dovetails for the acute angles perhaps they are doing something like this. William quoted that there are nuts and bolts used in the joints.

We can't see the seat face in the picture William posted. Perhaps there is a row of bungs across the front edge of the seat.

[Mark Singer]

Dave Your Good! Could be that ...or tenons or dowels...witk a good adhesive...

If they aren't using dovetails for the acute angles perhaps they are doing something like this. William quoted that there are nuts and bolts used in the joints.

We can't see the seat face in the picture William posted. Perhaps there is a row of bungs across the front edge of the seat.