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  1. #1
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    Default Biscuit Joints Min Board Thickness?

    Hi guys

    Iím after some biscuit joints advice please?
    Can anyone please tell me what is the minimum board thickness that you can use with a biscuit jointer?
    Iím mainly considering using 17-19mm boards and wondering if this is possible?
    Cheers


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  3. #2
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    Default

    Depends a bit on the timber. A dense hardwood should be alright at that thickness but I've seem softer stuff affected by swelling of the biscuit.

  4. #3
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    Hi Matt,

    Iíve used biscuits in 18 mm Pine, Tasmanian Oak and spotted gum a lot with no ill effects.

    Just make sure the glue is fully dry before planing or sanding afterwards, otherwise any ďbumpsĒ sanded flat will turn into indentations when the glue dries and the swelling subsides.

    To be honest, when edge joining to make a larger panel, I use very little, if any glue on the biscuits, as their primary function in that scenario is alignment, not strength.

    Kind regards,
    Lance

  5. #4
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    Matt

    I've used biscuits on boards less than half your proposed thickness. The blade on my biscuit joiner has a kerf of 3.2mm, I personally wouldn't think twice about using it on a 7mm board, if the purpose of the board required it to have biscuits.

    Personally I always glue biscuits, don't see why you wouldn't. While a biscuit does provide an amount of vertical alignment of a joint, it also provides an amount of reinforcing of the joint, put one in a vice and try snapping it in half, I'm sure you'll see my point.

  6. #5
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    Quote Originally Posted by Feckit View Post
    While a biscuit does provide an amount of vertical alignment of a joint, it also provides an amount of reinforcing of the joint, put one in a vice and try snapping it in half, I'm sure you'll see my point.
    No, no, no, it doesn't work like that

    Trying to break a biscuit in a vice has very little similarity to trying to break a join with a biscuit inside it.

    1) When a biscuit is in a join, the pivot point is the edge of the timber it's in, not the edge of the biscuit, so it's being pulled out, rather than snapped.
    Clipboard02.jpg

    2) Modern glues are stronger than the timber they're being used on, so, biscuit or not, a glued up panel is nearly always going to break in the middle of a board and not on the join anyway.

    Biscuits are an alignment aid only and shouldn't be relied on to add strength to a join.

  7. #6
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    Yes it does.

    I'll get back to that later.

  8. #7
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    Thanks everyone for your feedback. Greatly appreciated [emoji106]


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  9. #8
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    A biscuit in 17 or 19mm is ok .

    Go too thin like 9mm and the 3.2 kerf leaves 2.9mm per side at the biscuit .

    Biscuits swell with the glue when they go in and grab quick , that's good . But a week or two later and that moisture has gone and the swollen biscuit shrinks back a bit , not enough to make a loose join of it , but well and truly enough to stand out like Dogs Testes under a polish job if you only have 2.9mm left . Been there Done that. And there's no better way to remember than a job that costs wasted $$$ to fix.

    I leave at least 5mm on top if its a shiny surface. So if I was doing 9 mm and I had to biscuit it id be putting it low on the under side if it was to be shinny . And Id use a glue that doesn't swell the biscuit . like Poly or two pack.

    The good old well jointed boards and glue without biscuits can be very good instead of the hassle of biscuits as well . They last just as long .

    Rob

  10. #9
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    Default

    I have used a Makita biscuit jointer for ~20 years now with good success. The default layout for this machine is 18mm boards.
    Of course it works with other thicknesses as well, I've used it to align 70mm planks, and currently I'm building a wardrobe
    out of 12mm Meranti ply using size 10 biscuits. (not a good idea really - but it was the only hardwood ply I could get my hands
    on at the time I started the project) getting the 4mm slot in the middle of that is awkward.

    Not really trolling, but I am sure I'll get some differing opinions on the following:
    B.t.w. I roll my eyes when I hear 'biscuits don't add strength'. A biscuit adds surface to the joint - so you can think of it as an
    abbreviated spline or a very minor loose tenon. Added surface == added strength. The material of the biscuit makes one hell
    of a difference, by the bye - a compressed beech tenon is infinitely superior to a rubbery pine one (Lamello vs. Bix).
    Sure, a proper tenon would be stronger, as would be a full length spline, but ... I'd be interested to see some actual test result
    done comparing round dowels, biscuits and dominos to see how much, if any, they really contribute to the strength of a joint.
    Consider for instance that glue is weakest against torsion. I surmise that any of the aforementioned methods would greatly
    add to torsion resistance if [geometrically appropriate to load bearing] applied with that in mind.

    -Peter

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