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Thread: Making short boards longer

  1. #1
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    Making short boards longer

    Ever need a long board and only have short one? On boats it quite common to need very long boards and one of the many methods used to join shorter boards is a scarf joint. A cut at a very shallow angle on the end of two boards and then gluing them together. The shallow cut allows for a very large glue joint.

    The problem is always how to cut them? There are lots of ways and no one is right for everything. On plywood I just stack it up and hand plane it. This time I needed several 18'+ stringers and wanted a quick way to cut the joints. I simply can not find good clear lumber around here. So taking the best I can find and cutting out the knots and scarfing into longer pieces is the simplest and most affordable way to get long stringers.

    This is my second scarfing jig for the table saw. The first one scared the stuffing out of me! It had a tendency to trap the cutoff and the blade would quickly wedge the cutoff into the jig against the blade making a horrible noise!

    Now the cutoff falls off on the table with nothing to trap it. The air off the blade will tend to slide it back toward you but it has no speed and stops on the table.

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    Here is the recycled jig. You can see ii is very basic. The angle is approximately a 7 to 1 ratio. You just clamp the part and slowly slide it into the blade. Here is the results.

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    I ripped down several strips and then cut the knots out leaving me several different lengths. I took them and organized them to find my rough length of the stringer. Applied the glue to the cuts and clamped them down.
    God grant me the senility to forget the people I never liked anyway,
    the good fortune to run into the ones I do,
    and the eyesight to tell the difference.


    Kudzu Craft Lightweight Skin on frame Kayaks.
    Custom built boats and Kits

  2. #2
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    lotta folkswouldnt have heard of a scarf joint jeff thanks foir show us your jig.. i read somewhere about another old boat building joiint which was similar but it fixed a damaged board in the hull after it was done they cut out a area with a chisel and placed a new piece in its place kinda long oval shaped
    If in Doubt, Build it Stout!
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  3. #3
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    A dutchman? I think that is what they call that Larry. Never tried one but have read about it and seen photos. This joint has a lot of uses in woodworking but you rarely ever see it.

    I have a bunch more to make tonight and tomorrow.
    God grant me the senility to forget the people I never liked anyway,
    the good fortune to run into the ones I do,
    and the eyesight to tell the difference.


    Kudzu Craft Lightweight Skin on frame Kayaks.
    Custom built boats and Kits

  4. #4
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    Very nice and informative tutorial Jeff, thank you.
    In clamping do you need to "stop" the ends, to keep the boards from sliding apart?



  5. #5
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    Jeff, do you think if that joint is going to bear any stress, its integrity would be compromised as compared to one sollid piece?
    Last edited by allen levine; 11-26-2008 at 03:30 AM.

  6. #6
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    Quote Originally Posted by allen levine View Post
    Jeff, do you think if that joint is going to bear any stress, its integrity wouldnt be compromised as compared to one sollid piece?
    I doubt it, glue these days is often stronger than the wood.

    Neat tutorial Jeff, thanks!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
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  7. #7
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    Quote Originally Posted by Stuart Ablett View Post
    I doubt it, glue these days is often stronger than the wood.
    Stu nailed it. I read an unscientific test recently. Fellow cut and glued several joints to test the glue. I forget which glues he was using but the wood failed and joints held on every one he broke. So the joint was stronger than the wood.

    This joint has been used forever in structural members on boats. Matter of fact the plywood panel in my kayak are joined using this method and the skin is the structure. So it better not fail or I am going swimming!

    The parts I am making now are the frame members for a new boat I just started. So yea, I have a lot of faith in this joint.
    God grant me the senility to forget the people I never liked anyway,
    the good fortune to run into the ones I do,
    and the eyesight to tell the difference.


    Kudzu Craft Lightweight Skin on frame Kayaks.
    Custom built boats and Kits

  8. #8
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    Nice jig, Jeff

    If you have boards wider than the saw blade is tall, the way I have seen it done is with a sloped ramp on both sides of the board. Put a large base on the router with a straight router bit (or better yet, a good size flat bottom bowl bit) ... run the router across the board again and again, working your way up or down the ramp, until you have a smooth flat slope
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at www.solowoodworker.com

  9. #9
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    Quote Originally Posted by Jeff Horton View Post
    Stu nailed it. I read an unscientific test recently. Fellow cut and glued several joints to test the glue. I forget which glues he was using but the wood failed and joints held on every one he broke. So the joint was stronger than the wood.

    This joint has been used forever in structural members on boats. Matter of fact the plywood panel in my kayak are joined using this method and the skin is the structure. So it better not fail or I am going swimming!

    The parts I am making now are the frame members for a new boat I just started. So yea, I have a lot of faith in this joint.
    Good, Simple jig, Jeff. Dad & I used to cut quite a few of those, but by hand with a miterbox, (would sure have liked to have had a TS & your jig back then).

    Quote Originally Posted by Charlie Plesums View Post
    Nice jig, Jeff

    If you have boards wider than the saw blade is tall, the way I have seen it done is with a sloped ramp on both sides of the board. Put a large base on the router with a straight router bit (or better yet, a good size flat bottom bowl bit) ... run the router across the board again and again, working your way up or down the ramp, until you have a smooth flat slope
    That works pretty good too, Charlie, I've used that method three or four times myself.

  10. #10
    Yeah Jeff we use that joint even on the most expensive yachts. I have seen it used on a 20 inch wide plank, 3 inches thick running the port and starboard sides the entire length of a 94 yacht. That was the gunwhale and of course it was rounded over and tapered and made of teak.

    I watched 1 guy hand plane, then sand and finally apply epithane that gunwhale over the course of a year.That was all he did. It took forever, but when it was done, it was a gorgeous piece of woodworking with every splice done as you mentioned.
    I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"

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