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Thread: Table Top Cracking - What Did I do Wrong

  1. #1

    Table Top Cracking - What Did I do Wrong

    Would like some opinions on what I might have done wrong on this dining table top. It is constructed of solid walnut with bread board ends. The picture below shows a crack that has started (no doubt due to moisture changes) since the weather has started to change. It happens to be on the very edge of the table. I did my best to account for wood movement by gluing only the center tenon in the breadboard end construction. Since this is on the edge, there is no glue on this tenon and based on the location, it almost looks like it starts at the edge of the tenon underneath? Maybe I did not allow for enough side to side movement with the drawbore dowel?

    Secondarily, is there anything I can/should do at this point to repair it and/or prevent it from getting worse? Note, it is finished with Arm-R-Seal.

    table.jpg

  2. #2
    Join Date
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    Perhaps the slotted hole thru the tenon for the draw bore pin was too tight, and as the wood shrunk it became bound up on the pin, thereby not allowing it to move laterally when it tried to shrink. That’s my best guess, anyway.
    ---Trudging the Road of Happy Destiny---

  3. #3
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    John,

    I don't know what to say about what caused the crack. It could be the wood naturally releasing tension or seasonal changes in humidity.

    Personally, I'd wait until the crack has stabilized a bit and then make an "epoxy cocktail" used by turners to fill the crack. An epoxy cocktail is made by mixing epoxy and thinning it with DNA (denatured alcohol). When thinned it can be poured and will run into the crack. When the alcohol dries, it will harden although it's somewhat weaker I suspect. The hardened mixture can be sanded and buffed. I've used it on turnings.

    Sorry for your dilemma!
    Ken

    So much to learn, so little time.....

  4. #4
    Thanks, Ken, I'll give it some more time and see what happens. Thank you for this advice.

  5. #5
    That's what I'm thinking as well. I did purposely widen those holes, but maybe I didn't get it wide enough. Sigh, what a bummer.

  6. #6
    Join Date
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    360
    John, It's still solid. That's a minor cosmetic thing that only bothers you. I understand your quest to learn from the event. But I want to encourage you to enjoy that your solid joinery still serves and the crack only bothers you. Fill it with epoxy and enjoy the holidays without thinking about the crack. It's wood. Beautiful table.

  7. #7
    That may not be a seasonal expansion crack. it may be a drying crack. That board looks like it goes straight through the pith where the crack is. If yes, then it might have been stressed even before you glued up.

  8. #8
    Join Date
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    Drawbores can crack a piece as readily as gluing the tenons will. The drawbore pin needs to be tapered. When the wood shrinks and swells the pin moves up and down and will usually end up proud of the surface, but this movement prevents cracks. Never tap a proud, but tapered, pin back in flush and of course never glue it. Never use plain dowels as drawbore pins (caveat, see below), as they can lock in and make the cross grain situation worse than if it had been glued.

    I'd drill it out, let it sit for a few months, and then put a tapered pin in.

    A lot of auger bits were/are purposely made 1/64th over their nominal size. You can get away with plain dowels, maybe, if you've used one of these, and maybe even get away if you used a little bit of white glue on it. That said, the tapered pin is your best bet. As somewhat of an aside, Elmer's White Glue advertises that it's been made 'stronger' and I fear the flexibility a lot of woodworkers have counted on over the years may not be a reality now.
    Last edited by Charles Guest; 11-30-2018 at 12:11 PM.

  9. #9
    perhaps this is where i went wrong. I did use a standard dowel with an auger bit. Then i used a file to elongate the drawbore holes horizontally. Potentially stupid question... I'm very new to this, how do you make a tapered pin?

  10. #10
    Join Date
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    Quote Originally Posted by JohnM Martin View Post
    perhaps this is where i went wrong. I did use a standard dowel with an auger bit. Then i used a file to elongate the drawbore holes horizontally. Potentially stupid question... I'm very new to this, how do you make a tapered pin?
    Whittle them with your pocket knife. Or use a chisel and bench hook. S/B pretty much a straight taper from a relatively short straight section for apperance. You leave the top rectangular and untapered for a short distance, somewhat less than the distance from the top surface of the table to the thickness of the top mortise wall. If you make it untapered for the whole distance from top of table to the top of the tenon, you risk locking it in. It should still pull up tight. Drawboring requires more precision than a lot of people give it credit for needing.

    If the pin ends up too proud during after a few years, you can trim its head a little with a chisel but as mentioned never tap it back flush.

    To state the obvious, a crack almost always means something was too tight and/or constricted, whether glued, pinned, or both. The other causes could be wood too green, not allowed to acclimate to the shop, high humidity in the shop during the construction of the piece, breadboard too wide, lots of things.
    Last edited by Charles Guest; 11-30-2018 at 1:10 PM.

  11. #11
    Join Date
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    Take a normal dowel and a small block plane, sharp chisel, or whittlin' knife (whichever you have or are most comfortable with - even sandpaper wrapped around a block of wood) and start at one end and slowly peel material away to make a taper. Doesn't have to be a lot - usually 1/16" taper will be sufficient - just enough that the wood will have a direction to push/escape. Think the end of a pencil, just not so abrupt.

  12. #12
    Quote Originally Posted by JohnM Martin View Post
    Would like some opinions on what I might have done wrong on this dining table top. It is constructed of solid walnut with bread board ends. The picture below shows a crack that has started (no doubt due to moisture changes) since the weather has started to change. It happens to be on the very edge of the table. I did my best to account for wood movement by gluing only the center tenon in the breadboard end construction. Since this is on the edge, there is no glue on this tenon and based on the location, it almost looks like it starts at the edge of the tenon underneath? Maybe I did not allow for enough side to side movement with the drawbore dowel?

    Secondarily, is there anything I can/should do at this point to repair it and/or prevent it from getting worse? Note, it is finished with Arm-R-Seal.

    table.jpg
    I am not buying any of this tapered dowel/pin as a cure at all. I've never used tapered pins; I use regular dowels just like any other furniture makers do, and I have not experienced any cracks or splits (Japanese woodworkers use tapered nails (bamboo), but not for draw boring purposes).

    Gluing only the center tenon is not enough to deal with wood movement. Did you do the following?

    Did you elongate the holes on the tenons?
    Did you make the other mortises a little wider than the tenons?
    Did you have sub tenons? If so, how wide and long were they?
    How wide was the center tenon? If it was over 4" wide, you should not glue the whole center tenon.

    If you did not take care of the above properly, probably that's why you're in trouble with the crack. There is no guarantee that this is the only crack you will experience. Time will tell.


    Edit: I would not use epoxy to fix a crack. Inlay is my preferred method. But if you are going to use epoxy, use the flexible type (google to find it). But as others have suggested, don't do any fix until your table has undergone acclimation in its new environment (and if there are new cracks, you can fix them all at once). If it were my table, I would wait after a couple seasonal changes before fixing anything.

    Simon
    Last edited by Simon MacGowen; 11-30-2018 at 1:30 PM.

  13. #13
    Join Date
    Apr 2015
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    New England area
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    The wooden pin is tapered just like the steel drift pin you use to snug the joint up in the first place. Snug up with a tapered drift pin. Drive a tapered wooden pin into the hole.

    A drawbore will hold as tightly as glue, and produce the same cracking as a glued joint, unless the pin can wiggle just a little bit. A rived pin will also bend a little. The bend and the wiggle keep things from cracking. Otherwise, it's locked in as if it were glued. If you haven't experienced a failure, consider it a gift from the woodworking gods.
    Last edited by Charles Guest; 11-30-2018 at 3:25 PM.

  14. #14
    Quote Originally Posted by Simon MacGowen View Post
    I am not buying any of this tapered dowel/pin as a cure at all. I've never used tapered pins; I use regular dowels just like any other furniture makers do, and I have not experienced any cracks or splits (Japanese woodworkers use tapered nails (bamboo), but not for draw boring purposes).

    Gluing only the center tenon is not enough to deal with wood movement. Did you do the following?

    Did you elongate the holes on the tenons?
    Did you make the other mortises a little wider than the tenons?
    Did you have sub tenons? If so, how wide and long were they?
    How wide was the center tenon? If it was over 4" wide, you should not glue the whole center tenon.

    If you did not take care of the above properly, probably that's why you're in trouble with the crack. There is no guarantee that this is the only crack you will experience. Time will tell.


    Edit: I would not use epoxy to fix a crack. Inlay is my preferred method. But if you are going to use epoxy, use the flexible type (google to find it). But as others have suggested, don't do any fix until your table has undergone acclimation in its new environment (and if there are new cracks, you can fix them all at once). If it were my table, I would wait after a couple seasonal changes before fixing anything.

    Simon
    I think my error might have been in not elongating the dowel holes enough on the tenons. I did make the mortises wider for the sub tenons. I don't remember exact measurements.

  15. #15
    Join Date
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    Quote Originally Posted by Prashun Patel View Post
    That may not be a seasonal expansion crack. it may be a drying crack. That board looks like it goes straight through the pith where the crack is. If yes, then it might have been stressed even before you glued up.
    This is what I’m thinking you had a crack there from beginning. It’s still a good table that’s just building character
    Aj

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