box joint testing

[Leon]

Absolutely as do I. I was commenting more with the use with a lathe.

[Larry]

Jack wrote in news:n5ensf$i3s$ [e-mail]:

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.

[John McCoy]

Leon wrote in news: [e-mail]:

Well, as I recall the article (and as I posted above), the two joints broke in different ways. The M&T, all varieties including floating, sheared the tenon. The domino (and dowelmax, etc) all broke the mortised board.

I have no idea why that difference would exist, and I don't recall that the article went into any analysis of it.

It does seem to me strange that the mortised board should break at a much lower strain with the domino than with a floating tenon (where the mortised board didn't break at all).

John

[Leon]

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.

Understood! LOL

[John McCoy]

John McCoy wrote in news:XnsA5799D2B92E66pogosupernews@213.239.209.88:

Following up to myself, I found the article on line:

replete with pictures of the failed joints.

I was mistaken in thinking they didn't speculate on the different failures - it seems they attribute it to the domino, etc, being shorter than a typical tenon. Which I guess would depend on exactly what you were trying to join, but in their test pieces was the case.

John

[Leon]

Especially since a Domino is a floating tenon. BUT wood is not perfect and the pieces could have been weaker for one of the tests.

[Leon]

The fact that the Butt joint scored higher than two other methods makes the whole article suspect. I would not be surprised at all if the chart was sorted but not all of the columns were included in the sort. LOL

[dpb]

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.

[dpb]

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.

[krw]

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?

[-MIKE-]

And I was just commenting. You know me. ;-p

[OFWW]

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.

[Jack]

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.

[dpb]

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.

[John McCoy]

dpb wrote in news:n5f6ud$eg6$ [e-mail]:

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

[OFWW]

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?

[Leon]

Yeah and so was I. LOL Good on you!

[dpb]

...[preceding discussion elided for brevity]...

Ya' lost me there...no idea how is intended to relate to current discussion.

US FPL (Forest Products Lab) has performed extensive tests on the question and concluded "no"; in fact, the test data shows that the higher the clamping pressure, the stronger the joint up to the point of physically crushing the material. I've posted links to this in the (fairly distant) past and unfortunately don't seem to have a bookmark at hand so will leave it at that for now, other than to point out the specific testing (as is virtually all work by the lab) was done in support of the production manufacturer of wood products, and doesn't really reflect a home-shop rec woodworker environment. Consequently, the pressures achieved at the upper limit there exceed what generally would be found in work rec.wooodworking participants shops. Which simply supports the bottom line answer of "No" is why I included the discussion. (Leon may be the one exception here with his known penchant... :) )

The key limitation in a quality glue joint as far as material prep causing poor adhesion (other than that of ill-fitting joints) is have a fresh, unburnished surface. If one were to, for example, joint the material with a set of dull knives it's possible for them to "hammer" the edge rather than cleanly slice the fibers. In this case the micro-pores that are critical for the bonding to occur can be closed and thus the glue simply lays upon the surface instead of actually forming the bond. I forget, it may be that Hoadley in his tome on wood discusses; I'm virtually sure it's in the FPL Handbook (all again I've not looked recently to confirm).

[dpb]

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.

[John McCoy]

dpb wrote in news:n5he95$4g8$ [e-mail]:

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