box joint testing

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On Wed, 23 Dec 2015 20:43:50 -0000 (UTC), John McCoy

Thank you for the PDF link, now I can see what all the joints are. Seems disc's aren't too bad, and easy to do.
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On 12/23/2015 2:24 PM, John McCoy wrote:

and the pieces could have been weaker for one of the tests.

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On 12/23/2015 2:48 PM, Leon wrote:

As I said in an earlier response, "the results have no bearing as a general rule; they _only_ represent the actual joints as tested".
Of course a Domino is a floating M&T but you can see precisely why the two are so disparate in results in the test and in the order they are if you go look at the pictures. While the actual dimensions of the F-M&T in the test aren't given, it is obviously at least twice the width of the (single) Domino used giving it 2X the surface area each side plus twice the vertical dimension from the midplane (vertically) to resist racking force mechanically.
As so much of the other discussion, it's obvious just looking that it'll win; precisely how much I'd have guessed at the roughly 2X factor shown.
The problem with both the cope and stick and stub tenon in this test is there's no material left on the sides of any significance -- look at the failure mechanism, it split the two skinny sides while the glue joint remained intact. This is certainly going to be true as far as it goes, but one would never use such a joint in the case of the example justification in the leadin for the test of wracking forces like a chair rail; such a joint would only be found in a panel door or the like and there the panel would be there and provide the wracking resistance. I'll note the biscuit suffered a like fate--the glue is so strong it simply fractured the two remaining long-grain sides of the slot in the stile as their cross-sectional areas are so small given the depth is, like the stub and cope, so short there's no area over which to dissipate the concentrated tension force. That's the reason (besides that the tenon itself has bending moment resistance) the M&T does well, there's the full depth of the tenon over which the force is spread.
I think if one were to do similar actual geometrical comparisons of the rest there would be clearly recognizable reasons for them as well.
It's a case of comparing things that for the most part, shouldn't be compared in the overall rankings; only the minor differences between the similarly-sized and purposed joints should actually be compared against each other within a set of classes, perhaps.
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Well, the counterpart to what you just said is that you should consider the size of the joint when picking your joinery method. If a joinery method is constrained by the size of pre-fab units, it might not be suitable.
Of course, that's assuming you need maximum strength. As has been noted several times, for most applications all the joints are more than ample.
John
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On 12/24/2015 9:52 AM, John McCoy wrote:

I said _nothing_ whatever about actual application to any specific project; only discussing the limitation in attempting to drawing any generic conclusions from the test results as performed/presented. See the more detailed follow-on to 'Jack' I posted this AM.
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I never said you did, where do you get that from?

Well, the conclusion we can draw (at least, that I draw; you are of course free to not draw any conclusion from the information available) is that different size joints may require or benefit from different types of joinery.

I did see that, and don't disagree with anything you said.
John
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On 12/24/2015 1:26 PM, John McCoy wrote:

Perhaps I misinterpreted what you intended the response to mean...

I think that's a foregone conclusion for the specific project and joint within the project, yes. But I don't see that there's anything in the article as presented that really addresses the application issue in those terms, no.
IMO it is what is is and no more, no less--a comparison in isolation of a set of joints prepared independently and with no (cogent) forethought as to an actual test objective a priori. Hence it provides no information other than the basic fact of each those test results on its own.
It would have been interesting to have seen an actual comparison of, say, the Domino and beadlock systems under circumstances where they were geometrically-enough similar to see if either had any advantage over the other as a _system_ and then them as a class with respect to conventional construction techniques. But, it's simply not possible as the test was conducted. The closest there is to that would be within the miter with/without splines and the M&T with its variations of wedged/pinned; I _think_ w/o looking again at the article the latter were similarly-sized(?).
But, they didn't investigate haunched M&T, nor double nor the many other variations so from a structural standpoint in aiding a particular construction technique for a given application where true strength would be required it's also lacking for completeness.
I think again it's another patently obvious conclusion not needing any study at all that any/all as shown are sufficiently strong for a cabinet door or the like that the dimensions of the two pieces joined basically models. All in all, I thought at the time it was one of FWW's weaker offerings, truthfully (and this discussion has only strengthened that opinion).
Anyway, I've said all I've got to contribute; think I'll retire to Santa and the reindeer... :)
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The article didn't. I was extending on your point that a meaningful comparison would require the joints to be the same size, to suggest out that the differing results for different sizes indicate different joinery would be appropriate for different sizes.

I've always been dubious that the haunch on that style M&T contributes any strength (altho magazine writers invariably describe it that way). I think it's only real purpose is to fill the panel groove, and it came into existance because a stopped groove is a pain to make with hand tools.
John
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On 12/27/2015 8:17 AM, John McCoy wrote:

I simply made a reference to it (along with several others that you conveniently elided) that they didn't include many variations which would be needed to be able to draw more general conclusions of relative effectiveness of various types.
The point again being the article ranking of the various joints testing uniformly without consideration of anything else except the one result is simply mis-reporting the tests.
There's really no point in furthering trying to make more of it than it was...
--



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On 12/27/2015 9:17 AM, John McCoy wrote:

Tap Tap!
This has always bugged me as well. EVERY woodworking source on earth that mentions a haunched tenon bloviates about it's superior strength, when anyone that ever made frame and panel anything should know the issue is never strength, the purpose, as you said, is to fill the panel groove. The haunched tenon might be a tad stronger as measured by a rocket scientist, or an engineer, or any college pin head, but to a woodworker, it's only real and meaningful purpose is to fill the groove.
Glad someone else noticed this..'
--
Jack
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On 12/28/2015 11:32 AM, Jack wrote:

I made no posit re: strength and wasn't implying anything whatsoever -- as noted above, John conveniently elided the remainder of the list which again was simply that--a list--as denoting there's a "veritable plethora" of variations that weren't tested if one were to try to use those results to make more general judgments regarding suitability for other purposes which seemed (to me, anyway) the direction he was trying to take the discussion.
But, specifically, I was actually thinking of something much more like the following application at the time I was writing the comments, not just the simple panel-groove-filling version.
<http://www.woodworkersjournal.com/crisscross-corner-joints/ wherein there's a point in the construction itself besides cosmetics to provide clearance and yet the largest vertical height cross-section possible within the member.
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On 12/28/2015 1:37 PM, dpb wrote:

I wasn't referring to anything you said, I was specifically referring to John's reference to "magazine writers", as I appropriately quoted.
If you are one of those, only then would I be talking about you.
--
Jack
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On 12/30/2015 9:55 AM, Jack wrote: ...

OK, my bad...was thinking you were trying to infer that the reference as used I used it was intended to imply more than it was.

In print, but not outside technical literature of (I'm _absolutely_ sure :) ) no interest nor relevance whatsoever to woodworking... :)
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On Wed, 23 Dec 2015 20:24:28 -0000 (UTC), John McCoy

The "floating tenon" was smaller than the Domino, so the tenon on one broke, while the tenon split out of the board on the other?

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Just to be clear, the 3/8 M&T is the tenon thickness, not depth. The stub tenon looked to be about 3/8 deep from the picture.
The 2 I have a problem with are the miter and butt. Both would be at the very bottom if I were guessing.
Just reposting the results... Don't shoot the messenger.
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On 12/23/2015 2:16 PM, Larry wrote:

And just to be clear a 3/8" thick m&t is probably stronger than a 4 or 5mm Domino but probable not more than a 10mm Domino.
Apparently apples were being compared to oranges. ;~()

Probably a new writer that previously worked for Mademoiselle magazine doing the testing/internet fact gathering.

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On 12/23/2015 2:16 PM, Larry wrote: ...

Well, the butt is excepting for the two which again have no comparison owing to geometry as noted earlier.
As for the miter, the 45 angle increases glue area by the sqrt(2) factor so it's got almost 50% more for the same width pieces. Secondly, by cutting on the diagonal, the end grain isn't _totally_ end grain so there is a contribution of the side long grain that improves glue performance significantly as compared to the true-90 butt.
--


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On 12/23/2015 3:16 PM, Larry wrote:

Not shooting at you Larry. If you did the testing, _then_ I'd be shooting at you.
Posting the list is very interesting, allowing for some banter about joints. For me, I like Mikes points on common sense. Some common sense and a dash of experience and this list looks a bit funny to say the least. Swings sarcastic remark if it's on the internet, it must be true, also is on the money.
It's amazing to me how much bull is written in books. I'm oft reminded that the individual taste zones on your tongue was taught in schools for over 100 years simply because one guy wrote in down in a book and grade schools, high schools and colleges, including medical schools, taught it for a 100 YEARS, like it was true, and was bogus.
This list in my mind is bogus, and if I were doing the testing, and somehow a butt joint or miter joint came ahead of a domino, I'd keep it to myself, and try to find out what I did wrong in the testing. Just my opinion, but giant red flags here, making the whole thing suspect.
--
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On 12/24/2015 8:31 AM, Jack wrote: ...

The overall ranking is of little consequence, granted, because there's so much disparity between the joints as far as the specifics of them are concerned (as I've noted several times previously :) ).
Also, as far a postulating, that's well and good, but the results from a series of tests such as this are valid _only_ for the specific joints down to the specific sizes of the various mating pieces; one canNOT infer anything more than that regarding general conclusions.
To do the latter would require having a series of tests of each type in which the single variable under study _only_ is changed (say width of the tenon in the simple M&T for one) and then _only_ tenon length. The problem when one attempts to undertake this kind of study then becomes one that the number of tests required explodes geometrically and rapidly turns in to the thousands or 10s of thousands. That's where one would then need to turn to statistical design of experiments theory to develop a test matrix that would allow for at least some of the variables to be studied without confounding effects(*) with a reasonable number of tests.
But, for the particular set of joints incorporated, the simple butt did _not_ beat the Domino and there's an explanation for why the simple miter does as outlined above.
I don't think there's anything wrong with the tests themselves such as they were; it's simply trying to draw too many conclusions from the results that the amount of testing doesn't support.
(*) Confounding -- when an uncontrolled or unknown variable other than the one under test has an effect on the result of the device under test, the result of the test cannot be shown to actually have measured the desired effect of the intended variable. The example easily seen here is that between the M&T, F-M&T and the Domino the sizes of the tenons aren't controlled; only the type used. Hence, one had _no_ controls in place for the confounding variable and there's nothing that can be said specifically about the effectiveness of the joining _system_ at all; only that for the three specific cases with the specific dimensions that the results were in the order observed.
After nearly 40 yr of consulting in the area for which I coined the term "statistical engineering", being called in after the fact to try to make something of results from such tests as the above was all too common what a client was wanting. Unfortunately, in almost every instance, it was too late in the process to salvage the work done to date other than to try to complete an actual design for a series of experiments in which the tests run could be used to fill in the necessary test matrix.
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Brings to mind large laminated beam, what if one of the variables was mid point in the beam?
One of the questions nagging me is, the amount of pressure used on a glued joint. Is it really possible to squeeze out too much glue and render the project worthless a few years down the road?
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