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  1. #1
    rimcanyon's Avatar
    rimcanyon is offline Titanium
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    Its been about 15 yrs. since I had to buy some big dimension douglas fir and I was blown away by the pricing. 8x8 at $17.95 lineal foot, etc.

    Well I found some short (6') 8x8's cheap ($10 ea.). They were used as center guide rail posts and are being replaced by concrete barriers, but the condition is good. Problem is I need 8 to 9' 8x8's. I also need some 8 to 9' 8x12's. This is for a trellis that covers the walkway to the shop and house.

    I have a 20" bandsaw, so I can resurface the posts (they need to be rough to match existing).

    The question is, how can I splice the 6' posts to make 8' or 9' posts in a way that would maintain their strength and that would have reasonable aesthetics, i.e. joints that would look nice. I'd use clear epoxy, I'm not worried about longevity of the joint, just strength in an earthquake. Some kind of long splice joint would be best, since I have 3 feet of excess length if I am using two 6'ers to make a 9' post.

    Easy to fabricate would be a plus.

    -Dave

  2. #2
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    Rip down the center and insert steel plate?

    Would be ideal if you could rig up some sort of jig and track to cut the kerfs with a chainsaw

  3. #3
    JST's Avatar
    JST
    JST is offline Diamond
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    Posts only need to have compression strength, and reasonable bending strength. You won't have snow load, I'd guess.....

    How about cutting a tenon on one part's end, and a matching open-sided mortise on the other. Proportion for looks and reasonable strength. I'd make it about 2 to 2.5 thicknesses long.

    Then the glue should be good enough, but you could always thru bolt in two places if you want. Pretty strong, not too tough, can be made to look good.

    Why do you need 8 x lumber? I'm guessing for looks, the beam look...

    In that case, for your beams, either build-up the beam as a box, or if you insist, laminate some 2 x 12 lumber.

    For strength, there is also available laminated stuff. A friend who does small contracting just calls it "glue-lam". Almost any size available, very strong.

    For real bolted consreuction, you want the rings and washers that distribute the forces into the wood.

  4. #4
    Captain is offline Aluminum
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    Wood aircraft wing spars can be spliced with a scarf joint with a 1:12 taper. With todays adhesives, I would think a lap joint would work fine.

    Chris

  5. #5
    Chet Spencer's Avatar
    Chet Spencer is offline Aluminum
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    We Pipe Organ builder's do it with long scarf joints & tite bond III. Large pegs optional.

  6. #6
    Rod Frey is offline Plastic
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    One possibility is resawing them down the middle and bricklaying them back together.

  7. #7
    Airborne is offline Stainless
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    Half lap for sure, pinned with dowels.

  8. #8
    wippin' boy is offline Diamond
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    norm would mortice and tenon
    with a nice wooden pin

  9. #9
    pepo is offline Hot Rolled
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    A scarf joint creates the most area for glue. A butted scarf joint may be better in compression. An easy joint with a 20" band saw.

  10. #10
    pm
    pm is offline Senior Member
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    I have had a lot of fun setting up simple overlapping, tapered joints in some 12/4 walnut on my bridgeport.

  11. #11
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    Dave, all lumber, glu-lam, micro-lam or dimensional has gone sky-high. Long term building booms do that.

    As I'm sure you know, with posts, compressive strength is the primary concern.

    A butted scarf joint for a trellis would no doubt work but half-lap or mortice and tenon, maximizing the horizontal bearing would give higher compressive strength and more than enough strength to resist bending moment with the 3' lap, (minimum, with 6' material/9' post).

    The mortice and tenon would give the same bearing as a half-lap, with double the vertical bonding area. That with two, say, 1-3/8" dowels, (closet shelf pole) would be strongest.

    If perfect joinery would be difficult, (with a 3' lap in 8 X 8, it would be for me), I'd use a filling type of adhesive, possibly the expanding type, such as Gorilla Glue for mortice and tenon, (surface wiping joining) or epoxy for half lap.

    Were it me, I'd opt for the easier half-lap and epoxy as being a joint that would be easier to make and more than good enough. With the dowels and final rough sawing, I'd point it out to observers, should look great.

    Old carpenter Bob

  12. #12
    Charles Dolan is offline Hot Rolled
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    Dave,

    Rip your 6' down the middle and cut a common scarf joint at 4 times the thickness on the end of each piece glue them up straight and true and then glue two together with the scarfs at opposite ends facing opposite ways.
    I would use polyurethane glue, making sure that there is enough water in the joint to cure it all.

    Charles.

  13. #13
    stephen thomas is offline Diamond
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    If long term strength & durability is required, post in compression but must resist some side forces from earth tremors, I'd use a modified V joint with a squared off tips, and squared off shoulders. About 2" flat on the tip & about 1/2" flats at the shoulders. probably a 1:5 or 1:6 slope. The problem with 1/2lap, and to a lesser extent with single tenon is they don't provide much sideways resistance to racking in at leas one direction. My second choice would be mutiple tenon ("fingerjoint") and 3rd, a single tenon.

    Poly urinethane is a reaally pi$$ poor glue for this app. It does not have any strenght unless the contact is nearly perfect everywhere. It has almost the strenght of a syrofoam cup anywhere the glueline is thicker than about 1/3 the thickness of a sheet of paper. Go with your instincts and use Epoxy, I prefer WEST system.

    smt

  14. #14
    blackboat's Avatar
    blackboat is offline Hot Rolled
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    Stephen beat me to it; a butted birdmouth. And Charles has clued you in on a different way of doing it, at the cost of more epoxy putting the board faces together.

    And use epoxy.

    Rob

  15. #15
    Gary E is online now Diamond
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    Topic: OT - splicing WOOD beams
    rimcanyon


    The question is, how can I splice the 6' posts to make 8' or 9' posts in a way that would maintain their strength and that would have reasonable aesthetics, i.e. joints that would look nice. I'd use clear epoxy, I'm not worried about longevity of the joint, just strength in an earthquake. Some kind of long splice joint would be best, since I have 3 feet of excess length if I am using two 6'ers to make a 9' post.
    You start asking about BEAMS....

    Then you switch and talk about POST's...

    There is a HUGE difference in how you would connect / scarf/ combine / or any other term you want to use...

    Then you toss in just strength in an earthquake
    ok... that makes it simple...
    CALL A STRUCTURAL ENGINEER IN YOUR AREA.. one with the PE stamp

    http://www.nspe.org/

  16. #16
    surplusjohn is offline Diamond
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    with your band saw you could do one of those beautiful japanese joints that fits like a ball and socket and locks sideways. no glue, this would keep you busy for a while I suspect. BTW, that Gorilla Glue is way oversold in my opinion. makes a mess and if you can't do a super clamping job it is worthless.

  17. #17
    Charles Dolan is offline Hot Rolled
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    I defer to your greater experience and hereby withdraw my polyurethane suggestion unequivocally. I have only used it for small joints and liked it, and its weather proof characteristics made it seem ideal for this purpose.
    Epoxy is excellent but very expensive for jobs of this size so I was trying for a less expensive alternative. I will recommend resorcinol formaldehyde as a better substitute Weldwood or Cascamite, a brown powder mixed with water with excellent strength, gap filling and waterproof as well!

    Charles

  18. #18
    Rod Frey is offline Plastic
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    norm would mortice and tenon
    with a nice wooden pin
    If you mean Abrams, then you're right...

    Assuming that by "mortice and tenon" you mean "brad nail".

  19. #19
    chuckey is offline Stainless
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    For a quick and simple post, clean up the ends and use 4 1" diam oak dowels 12" long to stand one post on the other, use your favorite weatherproof glue. Don't forget to groove the dowels to allow excess glue to find its way out.
    Frank

  20. #20
    chrisfournier is offline Aluminum
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    I have done this on several occasions. The long scarf joint is the best option. 20 degrees to 30 degrees almost gives you ideal long grain glueing.

    With some very simple jigs you can clean up the joint faces very nicely. For true overkill you could the run splines down the length of the scarf joint to increase gluing surface and shear strength. These splines can be hidden of course...

    I would not lean towards epoxy, but would use polyurethane instead. Very strong, very weather resistant, very easy to clean up and easy on cutting tools when you are doing your final dimensioning! Epoxy can be very tricky to get it to wet certain woods properly and the clean up is ghastly.

    I would like to hear what direction you take and maybe see a photo or two! Vicarious living at it's best...

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