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Thread: Joining Plywood

  1. #1
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    Joining Plywood

    In building cabinets or any box, using butt joints and not using pocket screws, do you pre drill both pieces or just the starting piece?
    Tim in Hill Country of Texas

  2. #2
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    Clamp it up, predrill with countersunk holes, then screws.

  3. #3
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    I use biscuits and glue. I have never considered pocket screws as structural, just consider them as clamps.

  4. #4
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    If we are talking about screwing into plywood end grain the same rules apply as drilling pilot holes for MDF. The shaft of the screw should not apply any wedging action to the ply. Only the threads of the screws should bite into the material. The hole should be slightly deeper than the screw is long.
    Last edited by glenn bradley; 07-20-2022 at 1:14 AM.
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  5. #5
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    Quote Originally Posted by glenn bradley View Post
    If we are talking about screwing into plywood end grain the same rules apply as drilling pilot holes for MDF. The shaft of the screw should not apply any wedging action to the ply. Only the threads of the screws should bite into the material. The hole should be slightly deeper than the screw is long.
    Couldn't possibly agree more.

  6. #6
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    Quote Originally Posted by glenn bradley View Post
    If we are talking about screwing into plywood end grain the same rules apply as drilling pilot holes for MDF. The shaft of the screw should not apply any wedging action to the ply. Only the threads of the screws should bite into the material. The hole should be slightly deeper than the screw is long.
    Glenn is very correct. The same applies for thin wood applications.
    Lee Schierer
    USNA '71
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  7. #7
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    For butt joints, I clamp up, drill/countersink and then screw. I have two identical drill/drivers I use which greatly speeds things up. This is with or without glue, BTW. When clamping up, I use right-angle supports to help keep things as square as possible and then check/fix for absolute square when adding other components to the basic box. That's a lot easier if it's already square or nearly square. I do not generally use biscuits, dowels or Dominos for something like this unless there is a specific structural reason to do so.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  8. #8
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    Thanks all
    Tim in Hill Country of Texas

  9. #9
    Use assembly screws specifically made for the task. Drill point, and nibs under the head to counter sink them.

  10. #10
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    Quote Originally Posted by Richard Coers View Post
    I use biscuits and glue. I have never considered pocket screws as structural, just consider them as clamps.
    Yup that's what biscuits were invented for, to join sheet goods. They weren't intended to replace mortise and tenon joinery. I have some plywood cabinets fastened with biscuits only and we're 25 at years and counting on them. One is a microwave cabinet lag bolted to the wall and no sign of joint failure.

  11. #11
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    I have used biscuits for years to join plywood edges, but only for 1/2" thick or more sheet goods. And normally not where I need structural strength. Randy
    Randy Cox
    Lt Colonel, USAF (ret.)

  12. #12
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    Mitered, glued and screwed is probably the strongest joint.

  13. #13
    Clamp, align, counter drill, screw.

    Use screws with a smooth upper shank. I use a lot of Spax screws. Not really a big fan, but they are readily available. A lot of people use drywall screws but I hate them b/c they require such a large hole to accommodate the threads in the overlying piece & if you use a countersink drill big enough for that, the hold is too big for the threads to grip.

  14. #14
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    Quote Originally Posted by Tom Bender View Post
    Mitered, glued and screwed is probably the strongest joint.
    ??? For sheet goods? Please do explain.

  15. #15
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    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.

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