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Thread: Bonding to provide similar properties as the underlying wood

  1. #1
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    Default Bonding to provide similar properties as the underlying wood

    Following on this thread
    http://forum.woodenboat.com/showthre...with-wood-glue

    Duplicating the flexibility of the wood and its ability to handle tension compression and bending loads.

    My recollection of gluing wood was that the glued pieces were not as strong as the material (unlike welded metal)
    Are there now epoxy glues that are able to adhere and provide a bond as string as the underlying material?
    The stuff I see in the hardware store claims to bond metal to glass to plastic to wood to a bicycle!

    To hollow a stay mast, saw it in half, scoop out the middle and glue it back together, is it going to be as strong as if I took a 10' drill bit and drilled a hole? Anyone got numbers for these products (like youngs mod for example)
    Last edited by Magenta; 08-23-2020 at 01:23 AM.

  2. #2
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    Default Re: Bonding to provide similar properties as the underlying wood

    First off, epoxy, due to its soaking into the wood fibres provides a stronger bond than the surrounding wood.
    Second a well-made glued joint, following the best practice for the glue will be as strong as the wood. Epoxy does not like a thin glue line, Aerilite and Cascopgen are not gap filling and need perfect joinery.
    Many on here will recommend a flexible epoxy whose name escapes me for gluing spars.
    It really is quite difficult to build an ugly wooden boat.

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  3. #3
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    Default Re: Bonding to provide similar properties as the underlying wood

    G-Flex

  4. #4
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    Default Re: Bonding to provide similar properties as the underlying wood

    WEST SYSTEM–G/flex 650-8 Liquid Epoxy, Resin and Hardener

    (66) 4.5 stars, 66 Reviews , skips to reviews

    $32.99


    Thats some epoxy!

    Where would I buy 200 of those packs or a larger pot?

  5. #5
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    Default Re: Bonding to provide similar properties as the underlying wood

    On your side of the pond, you might have an easier time sourcing a local epoxy. Maybe Ampreg 36.

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    Default Re: Bonding to provide similar properties as the underlying wood

    Not sure about the Netherlands but the German main agent for WEST system materials is https://vonderlinden.de

    Helge von der Linden I know quite well.

    Cheers -- George
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  7. #7
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    Default Re: Bonding to provide similar properties as the underlying wood

    I doubt that your mast will ever flex enough to benefit from using G-Flex. There have been plenty of wooden masts glued up with regular epoxy resin over the last couple of decades (including some really radically bendy iceboat masts) which work just fine. The good marine epoxy resins are formulated to work with the natural characteristics of wood - meaning that the wood fails first, not the glue joint. You should be OK without needing to resort to a special flexible resin (which is itself not totally free of potential problems, like creep).

  8. #8
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    Default Re: Bonding to provide similar properties as the underlying wood

    Regular West system is significantly stronger than G-Flex, and has more than enough flexibility. The wood will break in tension long before the glue will fail.

  9. #9
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    Default Re: Bonding to provide similar properties as the underlying wood

    I've long been a proponent of glued spars, especially when you have slightly imperfect wood to start with. The glue joint will arrest the stress riser on a bit of grain runout and dissipate that stress into better wood.

  10. #10
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    Default Re: Bonding to provide similar properties as the underlying wood

    a properly made glue joint is stronger than the wood it joins. If end grain is not involved.

  11. #11
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    Default Re: Bonding to provide similar properties as the underlying wood

    I think the real question here is the strength of the structure, not the strength of the glue joint. If it is being compared to using a big drill bit in to essentially dig out the middle of a solid spar, making it hollow (as mentioned in the first post) the strength is going to be tied to the amount of wood left to do the job. Is the new hollow spar going to have suitable scantlings to replace a solid spar of the same diameter?

    Not knowing the boat or spar in question, it would then probably be a good idea to figure out whether it would really be a serious improvement, or just a lot of tedious work for little if any benefit.

  12. #12
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    Default Re: Bonding to provide similar properties as the underlying wood

    Quote Originally Posted by Todd Bradshaw View Post
    I think the real question here is the strength of the structure, not the strength of the glue joint. If it is being compared to using a big drill bit in to essentially dig out the middle of a solid spar, making it hollow (as mentioned in the first post) the strength is going to be tied to the amount of wood left to do the job. Is the new hollow spar going to have suitable scantlings to replace a solid spar of the same diameter?

    Not knowing the boat or spar in question, it would then probably be a good idea to figure out whether it would really be a serious improvement, or just a lot of tedious work for little if any benefit.
    No, it cannot. It has to be a bit bigger in diameter to compensate for the loss of material up the middle.
    Next assume a section formed in two halves, hollowed and glued together, if we increase the diameter to say 89mm (an extra 1/8″ in English) the calculated geometric comparison specifies an internal diameter of 52mm (wall thickness 19mm). We again check the permissible stress in compression, at 11.2 N/mm2 not OK. We must increase the dimensions to 90mm and 51mm respectively. This will give us 10.6 N/mm2, now OK.
    from https://albertstrange.org/designing-...masts-spars-2/
    It really is quite difficult to build an ugly wooden boat.

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  13. #13
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    Default Re: Bonding to provide similar properties as the underlying wood

    Well interestingly, these guys opted for polyurethane glue. anyone care to take a guess what brand?


  14. #14
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    Default Re: Bonding to provide similar properties as the underlying wood

    strength is going to be tied to the amount of wood left to do the job
    Yes. Assuming the section modulus of the remaining material is sufficient for bending and compression loads.
    Ideally this will be a large freestanding mast for a junk rig. the goal is an economical alternative to alluminum and ugly stainless rigging in all directions. There is just nothing more beautiful than a large wood mast (as the actress said to the bishop!)

  15. #15
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    Default Re: Bonding to provide similar properties as the underlying wood

    Quote Originally Posted by debenriver View Post
    Not sure about the Netherlands but the German main agent for WEST system materials is https://vonderlinden.de

    Helge von der Linden I know quite well.

    Cheers -- George
    Toplicht carries WEST as well...
    Heute ist so ein schöne Tag...

  16. #16
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    Default Re: Bonding to provide similar properties as the underlying wood

    Quote Originally Posted by Magenta View Post
    Following on this thread
    http://forum.woodenboat.com/showthre...with-wood-glue

    Duplicating the flexibility of the wood and its ability to handle tension compression and bending loads.

    My recollection of gluing wood was that the glued pieces were not as strong as the material (unlike welded metal)
    Are there now epoxy glues that are able to adhere and provide a bond as string as the underlying material?
    The stuff I see in the hardware store claims to bond metal to glass to plastic to wood to a bicycle!

    To hollow a stay mast, saw it in half, scoop out the middle and glue it back together, is it going to be as strong as if I took a 10' drill bit and drilled a hole? Anyone got numbers for these products (like youngs mod for example)
    The glue does not need to be stronger than the wood nor does it need the same flexible properties. Get the right glue for your job, that may mean long open time or ability to cure in your environment as much as adhesion. You dont need the "best" glue, just one that works, economy comes into it as well. PVA is stronger than epoxy for end grain as an example, great for indoor furniture but not great in mast construction. Any epoxy glue will do for a mast, but you need one with a slow cure when you're working with such big joints.

    A birdsmouth mast will be stronger that your theoretical hole because you can align the fibres to the load.
    whatever rocks your boat

  17. #17
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    Default Re: Bonding to provide similar properties as the underlying wood

    Quote Originally Posted by Paul G. View Post
    A birdsmouth mast will be stronger that your theoretical hole because you can align the fibres to the load.
    Very interesting comment. Having a hard time picturing this. Seems that the tree has evoloved to withstand benging loads from wind and compression loads from its weight and snow etc reasonably well. How do you align fibers better than that (im not even sure which direction fibers run in a tree... I presume from the center out and vertically? which is two directions)

  18. #18
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    Default Re: Bonding to provide similar properties as the underlying wood

    Quote Originally Posted by Magenta View Post
    Very interesting comment. Having a hard time picturing this. Seems that the tree has evoloved to withstand benging loads from wind and compression loads from its weight and snow etc reasonably well. How do you align fibers better than that (im not even sure which direction fibers run in a tree... I presume from the center out and vertically? which is two directions)
    If you start with a square stick with the pith running up its center, which is called boxed heart, then saw it in two, hollow it and glue it back together its annular rings will be the same as in the tree. However, if you just buy random stock and glue it together the annular rings could go in any direction.
    So if you build a birdsmouth mast from plank stock that is flat sawn you can place the annular rings in the correct orientation mimicking the tree.
    It really is quite difficult to build an ugly wooden boat.

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