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Thread: Joining Plywood

  1. #16
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    Quote Originally Posted by Tom Bender View Post
    Gladly

    Mitering provides the most glue surface

    None of the surfaces are strictly end grain.

    Adding screws adds strength.

    Screws can add clamping force to improve the glue up.

    Should the glue fail, belt and suspenders.
    A mitered glue surface is not a strong joint and I wouldn't put screws through a miter because there is way too little thickness for the head to hold well. It isn't strictly end grain, but it might as well be.

  2. #17
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    The same best practices apply to screwing plywood as to any screwed assembly: Clearance hole (the diameter of the screw shank) for the top piece, pilot hole for the bottom piece with the pilot hole at least the depth that the screw will achieve. And size the pilot hole on whether the wood is softwood or hardwood.

    Too many folk don't use clearance holes or pilot holes. And way too many folk use self drilling screws. But if you want to have the best outcome and not split your work, or strip your hole, then using the practice above is the one that will work and achieve far superior results.

  3. #18
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    Quote Originally Posted by Frank Pratt View Post
    A mitered glue surface is not a strong joint and I wouldn't put screws through a miter because there is way too little thickness for the head to hold well. It isn't strictly end grain, but it might as well be.
    A spline in the miter helps with that. A biscuit can be viewed as an easily created interrupted spline.

  4. #19
    If you use glue, it really doesn't matter how you hold it in place until the glue dries. I use glue and staples to build cabinet boxes for kitchens and bathrooms, anything more is just for fun.

  5. #20
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    Quote Originally Posted by johnny means View Post
    If you use glue, it really doesn't matter how you hold it in place until the glue dries. I use glue and staples to build cabinet boxes for kitchens and bathrooms, anything more is just for fun.
    That's not quite true. If you do not bore a clearance hole for the shank of the screw in the top piece, you risk not cinching the top piece to the bottom. What can happen is that the thread starts cutting its path on the bottom piece proud of the top piece -- e.g. there's a gap. This is why it is important to return to basics: not just pilot hole, but pilot hole PLUS clearance hole...

  6. #21
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    You all probably know this. Gluing end grain particularly with plywood can be greatly enhanced by first "basting" the end grain or plywood edge with watered down glue. Let it dry then glue as usual. The thin glue seals the pores and inhibits the second coat of glue from bein sucked into the end grain. Some folks say it makes the joint as strong as long grain to long grain. I do not know about that!
    Ask a woodworker to "make your bed" and he/she makes a bed.

  7. #22
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    Quote Originally Posted by Gordon Stump View Post
    You all probably know this. Gluing end grain particularly with plywood can be greatly enhanced by first "basting" the end grain or plywood edge with watered down glue. Let it dry then glue as usual. The thin glue seals the pores and inhibits the second coat of glue from bein sucked into the end grain. Some folks say it makes the joint as strong as long grain to long grain. I do not know about that!
    No need to water down the glue, just lay down a thick layer & let it sit 10 minutes, then glue it up. If you let the glue dry thoroughly it will interfere with adhesion. PVA glue does not stick to dried PVA glue. the resulting joint is quite strong, but not as strong as long grain to long grain.

    Biscuits are my go to for sheet goods. That's what they were invented for and they excel at it.

  8. #23
    Patrick Sullivan on youtube has a series called "Glue Myths" that is very interesting. He is very meticulous in his experiments and the data are surprising if you want to check it out:
    https://www.youtube.com/watch?v=m7HxBa9WVis

  9. #24
    Thanks for posting this - fascinating

  10. #25
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    Quote Originally Posted by Frank Pratt View Post
    No need to water down the glue, just lay down a thick layer & let it sit 10 minutes, then glue it up. If you let the glue dry thoroughly it will interfere with adhesion. PVA glue does not stick to dried PVA glue. the resulting joint is quite strong, but not as strong as long grain to long grain.
    The rational for basting end grain with watered down glue is to stop the glue at some point from just being sucked into the end grain. This is not my idea but rather another youtube experiment. I cannot find it. But I tried it and it works. The watered down glue actually disappears so there is no dry glue to wet glue issue.

    Cheers,

    Gordon
    Ask a woodworker to "make your bed" and he/she makes a bed.

  11. #26
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    Quote Originally Posted by Gordon Stump View Post
    The rational for basting end grain with watered down glue is to stop the glue at some point from just being sucked into the end grain. This is not my idea but rather another youtube experiment. I cannot find it. But I tried it and it works. The watered down glue actually disappears so there is no dry glue to wet glue issue.

    Cheers,

    Gordon
    I didn't mean to argue with your method, but present my alternate way. Both work. The important point is to not let the glue completely dry and cure before doing the second coat and glue up. It's surprising how much stronger you can make an end grain glue up using these methods.

  12. #27
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    it's all good
    Ask a woodworker to "make your bed" and he/she makes a bed.

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