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Thread: spliced lumber vs. single lengths?

  1. #1
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    Default spliced lumber vs. single lengths?

    Hi--

    Building a 20' canoe by the White Guide plans from Gil Gilpatrick.
    Getting very close to the stripping, so in a week I should be past the hull skin and onto gunwales, what 'deck' there is, and seats!

    So; do I need to find 22' knot-free ash for the gunwales? Or can I splace together with plenty of glue surface area the standard 8 or 10' lengths any lumber hard has?


    thanks!
    -Bernard

  2. #2
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    Default Re: spliced lumber vs. single lengths?

    Better pick up a 30' piece just to make bending easier. ,,,,,,, of course you need to scarph it.

  3. #3
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    Default Re: spliced lumber vs. single lengths?

    A simple epoxy-glued scarph at 10:1 slope will do nicely. Don't over-clamp it.

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    Default Re: spliced lumber vs. single lengths?

    You can also do the scarf joint with whatever adhesive you're using for the strips - waterproof adhesives are best but stuff like Titebond II isn't bad, either. As the gunnels get varnished afterward, the joint will stay pretty dry unless you let the canoe sit out in the weather or don't keep up with the varnish. (Using ash you will want to keep up with the varnishing as it turns black if not well protected.) Set yourself up a jig so that you can keep the pieces straight - either dado slots or spacers - and either wax the surface or cover with tape for a release layer - packing tape works pretty well here.

    The epoxy works well as Jim noted, but you have to be careful to keep from squeezing too hard and pushing it all out.
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  5. #5
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    Default Re: spliced lumber vs. single lengths?

    I gag at the thought of using anything but WEST System epoxy for building wooden boats of any sort. With the very gentle curves you have on a canoe, an 8/1 scarf will be fine.
    Keep It Simple: KISS it better.

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    Default Re: spliced lumber vs. single lengths?

    I'd agree with you Candyfloss, but I was kind of surprised to watch an experienced employee of a well-known boatyard try to scarf some mahogany and some ash (two separate scarfed sticks from the same material) using West System Epoxy. It took him three tries to get good joints.
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  7. #7
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    Default Re: spliced lumber vs. single lengths?

    Sometimes the most skilled shipwrights/joiners have a tough time with epoxy cuz they can not get their head around the gap/ no clamping thing. Please excuse my sarcasm from earlier.

  8. #8
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    Default Re: spliced lumber vs. single lengths?

    Having replaced ash gunwales on 3 strip built canoes, may I suggest using Mahogany in the first place?
    Never trust a man with a clean workshop.

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    Default Re: spliced lumber vs. single lengths?

    Material choice would depend highly on storage and maintenance, but lots of nice canoes with ash gunnels are on their "second set" around here - most of those because they were stored outside. I tend to agree with Lefty if you can't store indoors. Ash is not known for rot resistance and when the varnish gets scratched it goes from pretty to black and grey.
    "Anyone who says they like portaging is either a liar or crazy."
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  10. #10
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    Default Re: spliced lumber vs. single lengths?

    Whatever wood and glue you use, put a fastener through the scarf; one day you might need it.
    Last edited by amish rob; 06-10-2010 at 05:28 PM. Reason: add photo

  11. #11
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    Default Re: spliced lumber vs. single lengths?

    Ideally, your scarfs really ought to be about twice as long as that one.

  12. #12
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    Default Re: spliced lumber vs. single lengths?

    ......and less well fit!

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    Default Re: spliced lumber vs. single lengths?

    and without the fastenings

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    Default Re: spliced lumber vs. single lengths?

    The scarfs SHOULD be longer, but they are going on 9 years. I never like to trust any glue for fastening without mechanical back-up.
    If you saw the rest of the boat, you would believe these gunwales are strong enough for government work
    By the way, I really like that we all disagree all the time; differences make us all the same, eh?

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    Default Re: spliced lumber vs. single lengths?

    And without the fastenings. They can only weaken the joint. And install the gunnels so that the overlap runs from front to back. I'm not personally sure that it will make any difference in the long run, but I am told it is the right thing to do, so I always do it if I remember, or if it is not inconvenient.
    Last edited by Candyfloss; 06-11-2010 at 03:43 AM.
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    Default Re: spliced lumber vs. single lengths?

    I am totally amazed at the number of discussions on trying to decide on a 8 to 1, or a 10 to 1, or a 12 to 1 scarph......J.H.C....Just make all the scarphs 12 to 1 and all will be well. I have one jig that I set up for a 12 to 1 scarph and have never done less, or had one separate, whether using plastic resin, resorscinol or epoxy. Do the job right the first time and youse dunno gotta do it again.
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  17. #17
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    Default Re: spliced lumber vs. single lengths?

    Quote Originally Posted by BerniniCaCO3 View Post
    Hi--

    Building a 20' canoe by the White Guide plans from Gil Gilpatrick.
    Getting very close to the stripping, so in a week I should be past the hull skin and onto gunwales, what 'deck' there is, and seats!

    So; do I need to find 22' knot-free ash for the gunwales? Or can I splace together with plenty of glue surface area the standard 8 or 10' lengths any lumber hard has?


    thanks!
    -Bernard
    These guys might have something long enough.
    http://www.islandfallscanoe.com/old-...ls-repairs.asp
    For small amounts of special wood, look somewhere other than the lumber yards. I used to make canoes and got all my gunnel trim from a building truss manufacturer. They had mountains of 24' douglas fir, I explained what I was doing and they let me hand pick what I wanted and charged me cost.

  18. #18
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    Default Re: spliced lumber vs. single lengths?

    Quote Originally Posted by Canoez View Post
    I'd agree with you Candyfloss, but I was kind of surprised to watch an experienced employee of a well-known boatyard try to scarf some mahogany and some ash (two separate scarfed sticks from the same material) using West System Epoxy. It took him three tries to get good joints.
    What happened the first two times?

  19. #19
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    Default Re: spliced lumber vs. single lengths?

    Well, the first try looked to be starved for adhesive which would denote excessive pressure applied to the bonded joint.

    We could find no clear reason for the second failure. When we picked the stock up off the bench and did a trial bend, the joint failed. We wondered if the adhesive hadn't been mixed or cured properly, but it was very clear that the epoxy was well set. The failure ran through the bond joint and there were a few spots where it lifted from the surface of the scarf cut, but that the scarf joint showed epoxy penetration into the wood with no dry areas.

    The third time, the stock and adhesive were prepared exactly the same way as the second time, but the finished product was just fine and flexed without failure.
    "Anyone who says they like portaging is either a liar or crazy."
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  20. #20
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    Default Re: spliced lumber vs. single lengths?

    I was taught to put toothpicks inside an epoxy joint if the carpentry was too tame.

  21. #21
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    Default Re: spliced lumber vs. single lengths?

    I've grooved (~1/32" deep) one side of an epoxy joint to hollow it out like on a canoe keel. That way the surfaces meet at the outside and you have some room for adhesive and can apply good clamp pressure. I suppose you could do that when making the scarf joint, too.
    "Anyone who says they like portaging is either a liar or crazy."
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  22. #22
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    Default Re: spliced lumber vs. single lengths?

    I've heard of people putting a single layer of light-weight fiberglass, well wetted, in a scarf joint to prevent squeeze out when the joint is clamped.

  23. #23
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    Default Re: spliced lumber vs. single lengths?

    You can, but it's probably more trouble than it's worth. Let's not get too hung up on this glue thickness thing. The strength of the joint is the grain strength of the wood, not the thickness of the glue. What we want to do is (1) get the best grip possible on the two hunks of wood and (2) connect them as uniformly as possible over a long distance without gaps and with an adequate, but not excessive, amount of epoxy.

    Prep - Wood should be clean, dry and freshly sanded (60 grit by hand with a block is pretty good for structural bonds and leaves plenty of small nooks and crannies for the epoxy to grab onto). There is no reason to intentionally make a bad-fitting joint just so that it will hold a big blob of epoxy/filler mixture. That blob is not where the strength of the joint comes from. Filler mixtures themselves tend to be pretty stiff and brittle once cured, so excessively thick bands of filler between the two hunks of wood are not the answer - especially in cases like gunwale scarphs, where your trying to make two pieces flex as a single, continuous piece would.

    Once you get up into the 10:1-12:1 scarph ratios, you're getting into the range used for splicing aircraft wing spars. You're generating a lot of glued surface area (which is good) and both maximum strength and the most uniform flex characteristics in the finished piece. No metal hardware is needed or desired. It will just weaken things by concentrating stress in specific spots - the exact opposite of what we're trying to accomplish with a nice, long, smooth joint.

    The best way to start glueing is to mix just your resin and hardener and brush a coat on both surfaces. The function of this first coat is to soak as far into the wood as possible and to prevent the wood from sucking additional epoxy out of our joint as it sets-up. This step is how we make sure that we get a really good grip on the wood grain and it generates most of the strength of our joint. This initial coat does not need to cure before proceeding with step #2 (in fact, you don't want it to, in order to get the best bond between steps). It doesn't hurt though, to give the resin a few minutes to soak in before going to step 2. If the surfaces just seem to be soaking up resin like crazy, it certainly won't hurt anything to give them another coat (or more) before proceeding with the joint.

    Next, mix some filler into the remaining epoxy in the pot. This could be tiny milled fibers (cotton, linen, fiberglass, etc.) a high-density powdered filler like WEST 404, wood flour or other reasonably high-strength filler. The lightweight fillers made for fairing compounds (micro-balloon-based) aren't as strong and generally aren't a great choice for this job. We have already achieved the best grip we're likely to get on the two wood pieces with step #1, so step #2 will be to join them without leaving any gaps. The filled resin doesn't need to be terribly thick, in terms of its consistency, we just want to be sure that it will stay in the joint while we get everything aligned and clamped, and hang into any little craters that need filling. Brush a healthy coat of the filler mixture onto the wood and join the two hunks. You want enough clamp pressure to make sure that everything stays aligned and so that as the joint comes together you're squeezing some filler out all around the joint. There is nothing to be gained by a thick line of filler between the wood pieces or a sloppy-looking joint, but you do want to make sure that your clamping process isn't squeezing all the filler out from between the two pieces. Firm, uniform pressure along the joint is usually a lot better than a couple of C-clamps cranked down hard and concentrating the force in specific places. This might mean using long-ish wooden strips as clamping pads between the clamps and the joint to spread the clamp pressure more evenly (tape or plastic covered to prevent sticking to the joint) or using less powerful clamps (including stuff like inner-tube bands, spring clamps, etc.) but more of them. This is one reason that vacuum bagging works well with epoxy. It tends to supply lower clamping pressure very evenly over large areas, rather than lots of pressure concentrated at just a few spots.

    Once cleaned up, your epoxy-glued joint may not look quite as tight and invisible as you might generate with high clamping pressure and other glue types where you can virtually eliminate the glue line, but it should still be quite neat, and most likely, the strongest and smoothest way to turn those two short pieces of wood into one long one.

  24. #24
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    Default Re: spliced lumber vs. single lengths?

    Todd--Thank you for posting that detailed process description. I learned a lot.
    Paladin--You mentioned a scarfing jig. Do you (or anyone else here) have pictures of your jigs to post? Thanks for the explanation!

  25. #25
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    Default Re: spliced lumber vs. single lengths?

    Dont' forget that the scarf joints in your gunwale/rubrail need to be nibbed, rather than plain scarfs. The reason being that the feather edge on a plain scarf is fragile. Here's a nibbed scarf (ignore the bolts and backing plate shown):



    Here's a plain scarf:

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  26. #26
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    Default Re: spliced lumber vs. single lengths?

    Hence the screw, in the meat, near the end. Screwing the gunwales together anyway, way as well support the ends a bit. Again, just me, not right

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