splayed leg structures

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Jon B
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splayed leg structures

Tue Feb 10, 2015 10:24 pm

I've been working through TAJCD IV, and have been thinking a lot about the geometry of square vs "diamonded" legs at compound slope, and about the intersection between cross members (stretchers) and the legs. It got me wondering how others deal with this issue, so I started looking around at woodworking magazine websites for info on splayed leg structures. I came across two plans, one a table and one a stool. Both table and stool utilize compound slopes for the legs, and both also have square legs in cross section. The table has a pretty minor splay of 4 degrees, whereas the stool is more like 15 degrees. Neither article talks about the fact that the stretchers or aprons (in the case of the table), will not meet square with the legs, as it is outlined in TAJCD IV. I drew up some quick sketchup models of both situations, to confirm that the designs would leave gaps between the cross members and legs when both are cut square, and indeed they do....though the table has such a minor amount of splay that the gap between the legs and the aprons is very minor.

Anyhow I guess I find it really puzzling that the connection between compound splayed legs and cross members (at least in the cases I found) are not addressed at all. Am I missing something or are the authors just breezing over the finer details to make things easier to build?
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Yxoc
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Re: splayed leg structures

Wed Feb 11, 2015 2:56 am

G'Day Jon,
Can you provide a reference or link to the articles?

Derek
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Jon B
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Re: splayed leg structures

Wed Feb 11, 2015 7:42 am

Hi Derek, here are the articles
http://www.finewoodworking.com/fwnpdffr ... -table.pdf

and the other is on page 40 of this page:
https://books.google.com/books?id=7fYDA ... ol&f=false

I also attached a couple of really quick images from sketchup showing a similar situation to what is described for the stool, with the legs square in cross section, at a 15 degree angle, and with an apron between the legs cut with a square butt cut... hope that makes sense.

I think either I'm missing something and the designs for these two pieces would still result in tight joinery, or the authors ignored the small gap produced at the intersection of leg/cross member. Also, I believe if the gap was ignored it would face the inside of the stool or table, and so would appear tight from the outside... but I also think it would require a bit of looseness in the joinery.

Sorry for the long post about this, I just find it curious and wonder if anyone else has ever come across situations like this or analyzed the design of other work that didn't quite seem right.
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gap.jpg
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stool legs.jpg
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Chris Hall
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Re: splayed leg structures

Wed Feb 11, 2015 9:47 am

Jon,

I share your surprise, however I have long moved on from such surprise that this matter is not covered really at all in Western practice.

In only one western book, a Ranford text on using the steel square from 1906, did I find any reference to this problem, where he shows a simplistic method of backing the post after the timber has had its end cut to meet the floor cleanly.

It's really bizarre to me how little this subject has been covered in Western carpentry despite the inherently very basic arrangement of a wooden structure having splayed legs. So many structures have had this form. Maybe some folks figured it out in the past, but they appear to have kept their approach and solutions to themselves. The French cover it in certain ways, however as often as not they deal with a splayed leg by rotating the leg entirely so as to bring one face into alignment with the prism rather than changing the leg shape. As expected, this results in some joinery issues, and as often as not the connections in that sort of French work are spiked together.

You are correct that with slight slopes the effect is less pronounced. In fact, doing this form of compound joinery work when the leg splay is slight is more challenging than otherwise. Still, geometry is geometry, and if the leg shape is not adjusted then the joinery problems arise elsewhere.

Both articles linked, reveals how the geometrical issues are usually avoided - - the joinery employs floating tenons for the stretchers rather than through tenons, or the stretchers only have stub tenons. These are weaker, glue-dependent connections it should be noted.

The Garrett Hack article annoyed me when it first appears and continues to annoy me on the re-read. Yes, he doesn't seem to mention cutting the top/bottom stretcher abutments at a slight angle. I decided to do a quick Sketchup model myself to see how close he would be, given the 4˚ splay angle mentioned in the article:
4˚ splay.jpg
4˚ splay.jpg (41.85 KiB) Viewed 5844 times
As you can see, on the top/bottom stretcher surfaces, a 90˚ cut would be out by 0.14˚, And the apparent error on the broad faces of the stretcher is negligible - likely a sketch Up error.

I also drew the stretcher lower down, without the upper surface beveled to match the top of the leg to confirm that the 90˚ angle would still be out (should be the same as the above drawing), as he processes the cuts with the stretcher as a rectangular section:
4˚ splay 2.jpg
4˚ splay 2.jpg (45.79 KiB) Viewed 5844 times
Yup.

My guess is that he assumed a slight cut out error and simply made a little adjustment to the tenon shoulders after he tried the fit. Or maybe he just clamped it up tight and kind of squished the grain down on the leg. Maybe the cock-beading covers it up a bit too. I don't know, but it is articles like that which have led me to not bother with that magazine any more.

If the leg shape is not backed, then the stretcher top/bottom edge bevels are obviously going to be different, however the connection can certainly be made cleanly - if Hack had taken any time to actually explore the work he is tackling to a more detailed level, he could have cut the stretcher end cuts to the correct required angle to meet an un-backed leg cleanly.

As soon as you have a through tenon however, then the issues of centering the tenon in layout would crop up and surely be noticed, though who know, maybe i overestimate what people notice or don't notice? If the connection is blind, this compound reality just passes without notice.
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Jon B
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Re: splayed leg structures

Wed Feb 11, 2015 9:55 pm

Thanks for the great reply Chris.

Another thing that I've noticed doing some brief google searching for splayed leg furniture is that many pieces employ turned legs and spindles, which seems to be another way of avoiding some of the geometry issues that arise. And it looks like a lot of the pieces that employ non-turned legs avoid the use of stretchers.

In any case I'm glad to be learning the process of building with splayed posts through TAJCD. It's definitely a challenging process particularly the connections between the legs and stretchers. I spent a good chunk of my time today laying out the mortises on the legs of my splayed leg stool, making a lot of mistakes but finally I think I got it. Now for the actual cutting part....
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Yxoc
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Re: splayed leg structures

Thu Feb 12, 2015 2:17 am

Jon,
Don't forget to share pictures of your progress.

Regards

Derek

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