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Thread: capping endgrain or how not to split a tenon?

  1. #1
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    capping endgrain or how not to split a tenon?

    Hi All, the attached photo is my version of a wood tray I saw on Scott Meek's webpage. When I made it, I tenoned the maple boards into mortises cut into the wormy pecan endboards. As a decorative bit I tried using brass pins instead of square pegs like Meek did. In any case, I pre-drilled for the pins and drive them in and everything seemed fine..until finishing when I noticed one of the tenons had hairline cracked, progressing into the cutting board by 2 inches I am assuming this was because there was already a defect in the maple I had not noticed and the pin exacerbated it.. But all of this brings me to the question of how to design this best. I made two smaller tenons on each end rather than one long one, each tenon was about 2.5 inches wide and 1/4 inch thick, 3/8 long. This is a wide piece (about 10 inches) and I was wondering in general if when designing a cross grain joint like this what I need to be careful about. I know I could but the whole board into a frame but that would be hard to keep clean..

    Nicole
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  2. #2
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    Nicole, can you show a picture of the tenon with the crack in it ? Does the crack run through the tenon or along side of it ? In fact, is it a true tenon of is it a peg / pin inserted into both pieces ? I'm trying to figure out what actually cracked.

  3. #3
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    This looks like the classic "breadboard end" situation. When joining pieces in a cross-grain situation like this, you need to design in a way for the wood to expand and contract without joint failure.

    Imagine that maple panel shrinking in width. What happens at the brass pins? The wood can't move toward the center like it wants to because it is restrained by the pins, so it cracks.

    If you want to do this successfully, make slotted holes in the tenons for the pins, so the ends stay tight to the panel, but the panel can expand and contract with humidity changes.

    Breadboard End (12-8-14).jpg

    Beautiful tray, by the way. At this point, I'd probably keep my fingers crossed that the crack doesn't grow.

  4. #4
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    >>>> wondering in general if when designing a cross grain joint like this what I need to be careful about. I know I could but the whole board into a frame but that would be hard to keep clean..

    It's your maple center field that is causing the problem. Unless you design a way for the center panel to expand and contract without hinderance, you will have the potential or splitting and/or other damage. Your brass pins and a significant part of the problem. They look to be hindering the center panel to move up and down (as shown in you photo).

    You can't stop the expansion/contraction, you have to design for it.
    Howie.........

  5. #5
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    Quote Originally Posted by Yonak Hawkins View Post
    Nicole, can you show a picture of the tenon with the crack in it ? Does the crack run through the tenon or along side of it ? In fact, is it a true tenon of is it a peg / pin inserted into both pieces ? I'm trying to figure out what actually cracked.
    Hi Yonak, it would be tough to show in a photo. It is a hairline crack that looks like it starts right where the brass pin went into the tenon and then it propagates into the maple center board. The crack can be seen from both sides of the board. This is a true tenon, mortised into the darker endcap. Hope that is clearer!

  6. #6
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    Jerry,thanks for the comments and suggestion. I never would have thought of a slotted hole for the tenon pins!

  7. #7
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    Thank you Howie, I think the lesson is clear for me! I made a table recently and I ran the tenoned apron pieces into mortises in the legs. Same situation- the tenons will expand and contract while the grain in the legs runs in a different direction and should have a lesser degree of dimension change than the tenon. All my books and readings say that is OK, but in that case, the apron is only ~ 4" whereas the board I made here is wider at 10 inches...

  8. #8
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    Quote Originally Posted by Nicole Wood View Post
    but in that case, the apron is only ~ 4" whereas the board I made here is wider at 10 inches...
    That's exactly right! We get away with cross-grain glue joints when the pieces are small and stable, but run into trouble when the parts get wider. Species matters too, as does the "cut" (meaning that quarter-sawn lumber moves about half as much as flat-sawn, so a QS apron will work better than a FS one).

  9. #9
    I suspect that the others are correct about the cause of the cracking.

    On a slightly different note, I would have made the maple tenons longer than 3/8". The rule of thumb for tenons is that they approach max strength at 5x their thickness, or 1 1/4" in your case. This also provides a bit more "meat" when pinning (especially if drawboring), otherwise you risk having the pin blow out the wood between it and the end of the tenon.

  10. #10
    As an aside to the crack/wood movement issue its worth noting that while its an attractive tray, such joinery is really not great for any type of item that will need to be, or could possibly be, washed. Those bread board ends will require the bulk of the joint to be left dry. This means if the item is to be used for food, or any service that will require washing, the joints are a haven for all things nasty. Beyond that, water getting into those joints will foil any finish applied.

    I mention this only because if an item is meant as a gift or for sale, its nearly impossible to educate the user as to how it should or souldnt be used.

  11. #11
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    Chris and Mark- thank you both for your comments. The stubby tenons were the result of sloth on my part, using a router bit with a bearing that left me 3/8 inch. I am not well set up to make a deeper cut and though I have cut them by hand before I was not up for doing it this time. Point well made though about strength! Mark, your points sort of make all these questions moot..I hear you about food cleanup and had not really thought that through..thanks a bunch! ( I wonder if the 10 second rule might apply..)

  12. #12
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    Following up on Chris' post, the stubby tenons will increase the likelihood of a crack by not having enough "meat" beyond the pin to resist splitting, even when the joint isn't so wide.

  13. #13
    Quote Originally Posted by Nicole Wood View Post
    ( I wonder if the 10 second rule might apply..)
    It most definitely would. I wouldn't hesitate to make a tray like that for myself however if you imagine a gift or sale item and the tray gets used for cheese, summer sausage, prociutto (sp), and the user doesnt simply wipe with a damp rag but rather wets the tray with a soapy dishtowel your sunk. The water is going to saturate the joint. Drying will be extremely slow and combined with what was on the board and in the water will lead to a slimy black mess colonizing the joint.

    Its sad, but true. As a user of your own goods its of little issue but when you cross that line all things change.

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