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Thread: FWW Joint Strength Test

  1. #1
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    FWW Joint Strength Test

    So this should be a doozy of a thread in which to discuss the findings that FWW did on 18 different ways to join, basically, a stile and rail.

    The half-lap joint won for the strongest joint.

    It was VERY interesting how/where the various joints failed.

    I don't have the mag in front of me but I will later today and I can fill in more infor if someone else doesn't.

    Dowelmax beat Domino but trad M&T beat both of them and I forget where the floating tenon came in....
    Wood: a fickle medium....

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  2. #2
    Quote Originally Posted by Chris Padilla View Post
    So this should be a doozy of a thread in which to discuss the findings that FWW did on 18 different ways to join, basically, a stile and rail.

    The half-lap joint won for the strongest joint.

    It was VERY interesting how/where the various joints failed.

    I don't have the mag in front of me but I will later today and I can fill in more infor if someone else doesn't.

    Dowelmax beat Domino but trad M&T beat both of them and I forget where the floating tenon came in....
    What issue are we talking about Chris? Maybe it will be in the mail today? Clifford

  3. #3
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    The thing that surprised me was the bridal joint. They didn't include that on their last test, and I assumed it might come out a bit ahead of the half lap due to more glue contact. Instead it comes in just slightly behind the half lap. Obviously the wood thickness of the joint parts must be playing a part here too.
    Use the fence Luke

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    Quote Originally Posted by Clifford Mescher View Post
    What issue are we talking about Chris? Maybe it will be in the mail today? Clifford
    Yes, mine arrived in the mail last night.
    Wood: a fickle medium....

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  5. #5
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    Quote Originally Posted by Doug Shepard View Post
    The thing that surprised me was the bridal joint. They didn't include that on their last test, and I assumed it might come out a bit ahead of the half lap due to more glue contact. Instead it comes in just slightly behind the half lap. Obviously the wood thickness of the joint parts must be playing a part here too.
    Yes, wood thickness and glue surface area are the two items that stand out for maximizing the strength of a joint for the specific racking test they were doing.
    Wood: a fickle medium....

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  6. #6
    Quote Originally Posted by Chris Padilla View Post
    Yes, mine arrived in the mail last night.
    Yep, it just arrived in the mail. Interesting. Dowel Max beat Domino but suspect that Festooligans will complain that they used only one domino. Clifford.

  7. #7
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    We had to pull the thread but Jim Lindsay, Dowelmax inventor, had some issues with the testing.

    I need to go back and read more carefully everything they did and calculate glue surface area and such to get a better comparison feel but I thought FWW did a good job of TRYING to make fair comparisons.

    One thing they need to touch on more is WHAT is an appropriate strength. What does surviving 1000 lbs/area pressure buy you over "only" surviving 500 lbs/area pressure? Is it much? Does it depend? Is 500 good enough?

    Since the trad M&T is pretty well time-tested, I think using its numbers is a good place to start. Old chairs rule here....
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  8. #8
    Here is what I took from this article - nearly all of the joints held where there was contact. So, the Domino joint failed at the termination point of the Domino, the dowel joint failed at the termination point of the dowel, etc. In those situations, the stile fractured along the grain. I don't have the article in front of me either, but seems the wood was cherry. That being the case, it was the wood that failed - not the joint.

    The test really is deceptive in that regard. If there is sufficient force on the wood to fracture it, then I don't know that this test has much practical application, except to say that some of the methods just simply do not have enough glue contact, i.e., stub tenon, cope/stick - for cherry or whatever wood was used. Oak may produce a different result.

    Most of my projects are not built for use in a military environment. While I am now a Domino owner (gloat, gloat!!), I don't think this test effects my attitude toward any of the joints that I may use in various applications.

    Ultimately, these findings should give us some valuable information to use in deciding which joints to use where. And, that is all. I am not going to start putting everything together with half-laps just because they are the strongest. That just is not practical, nor necessary.

  9. #9
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    I always find these interesting as well. Obviously, part selection can vary these results so multiple tests of each joint help homogenize the result..
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

  10. #10
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    Quote Originally Posted by Clifford Mescher View Post
    Yep, it just arrived in the mail. Interesting. Dowel Max beat Domino but suspect that Festooligans will complain that they used only one domino. Clifford.
    I just bought a Domino so I have to assert that the test has to be flawed.

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    Quote Originally Posted by Michael McCoy View Post
    I just bought a Domino so I have to assert that the test has to be flawed.
    Being a Domino owner, I was thinking as I read the mag that Festool needs to come out with a larger/longer domino and associated cutter!
    Wood: a fickle medium....

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  12. #12
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    Festooligans! I love it! Good one Cliff.

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    Quote Originally Posted by John Keeton View Post
    ...it was the wood that failed - not the joint.
    The test really is deceptive in that regard. .

    Funny thing, I was logging in to see if anybody else had read this article, just got my copy last night and was reading it at lunch. My impressions are similar to the exerts listed above from John's insightful thoughts.

    I find these tests nearly meaningless and banal at best. What I see on careful examination of the pictures is a series of joints that held fast and a series of long grain fractures on the edge of various pieces of cherry. I am not quick to jump to any conclusions about each joints average strength, nor am I ready to change any methods I use or purchase new tools or lose old ones based on this testing method. Though I am strangely pleased that my old friends the half lap and bridle joint scored so well on the test anyway; these were the first joints I learned to make after all.

    Do they assume that every piece of cherry has the same relative strength to begin with? Look at the pictures, look at the thickness of the annual ring spacing and ask your self "Is it possible that the weakest cuts of wood are the first to fail irrespective of the joinery involved?" This is after all a natural product with gross variations of strength over its range, not a standardized fabrication like steel or aluminum. Or is the suggestion that the deeper into the edge of a style a rail joint penetrates the greater the strength it will provide before the inevitable wood failure?

    I further wonder how each joint may sustain a 'shock' force rather than a long slow crushing as created by the servo-hydraulic testing machine. Suppose a portly friend sits in a chair you have crafted. Will he gently lower himself down, adding weight incrementally? Or will he plop his but down hard and take a load off? Does it make a difference? How about child swinging from a cabinet door? (not that I ever did this as a child mind you...)

    Wood being a naturally flexible product seems able to bend a bit as force is applied but some wood seems to break more easily when force is applied in a quick sharp manner. Ever break a sticker or thin cutoff over your knee? Bend it and it will bend considerably. Smack it on the edge of a stout table, and it will break. The editors in FWW do suggest in a sidebar that the test results are not indicative of a joints potential to withstand the stress of seasonal movement and use over time. Not sure how to simulate these factors in a lab, but without taking them into consideration what use are these tests really?

  14. #14
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    I got it last night as well and agree ther are some flaws...one I saw was that for a pretty wide joint, it looks like 1.5 inch dowels were used instead of 2 inch, and yes a second domino would easily fit in the joint they showed. If I did use my dowelmax (ninja gloat) for such a wide joint I would use the longest dowels I had available, maybe even make some of my own from dowel rods to be long enough. Or maybe Jim needs to find a supplier who can make compressed dowels in 2.5 to 3 inch lengths
    That which does not kill you will likely raise your insurance premiums.

  15. #15
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    Perhaps it is splitting hairs decide if the wood broke or the "joint" broke. To have a joint, it involves putting together two or more pieces of wood. If the joint fails, it fails: be it the glue failed or the wood failed.

    Since they used cherry, that kinda sorta cancels out through all the tests. Yes, being a natual product, no two pieces are EXACTLY alike so you have to take it with some grain of salt so add a tolerance of +/- 10% (or whatever) to all the numbers read of the test machine.

    LMOL neglected to bring in my mag for lunchtime reading so I cannot comment much further on the details of each joint, size, glue area, etc. of each joint to see if they matched them up well or not.

    Ultimately, and I'm drawing similar conclustions as everyone else I think: it comes down to glue area and wood "thickness" per se. Maximize this within the joint and it appears that it will be stronger according to this testing method.

    It is an interesting test and it would be further interesting to see other tests like the shock one that Peter suggested.
    Last edited by Chris Padilla; 12-19-2008 at 3:20 PM.
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

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