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Thread: joining legs to a nested torsion box in an outdoor table...

  1. #31
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    Quote Originally Posted by lowell holmes View Post
    I would probably use a piece of 1/2" exterior plywood. We used to make long beams in residential construction with two 2x12 boards with 1/2" plywood sandwiched. That gave us 3 1/2" in width, which fits standard 4" board widths and it is strong.
    You're missing the point, aren't you? The steel flitch plate is for strength, not thickness. Steel is way stiffer than plywood.

  2. #32
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    Quote Originally Posted by Matteo Lorenzo View Post
    ...and since the facility i found locally that sells this stuff only sells in 20ft spans, would it be considered logical and safe to go with 10ft of reinforcement on either side instead of the full 12'1" that the beam spans?...
    Yes, you should be okay. In fact, there might be a little advantage in holding the steel short of the beam ends. The steel may rust (if it ever rains in CA again). If the steel extends over the legs, rust stains might drip down the leg faces. But if the steel stops short of the legs, any rust drips would fall to the ground.

  3. #33
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    Quote Originally Posted by Jamie Buxton View Post
    You're missing the point, aren't you? The steel flitch plate is for strength, not thickness. Steel is way stiffer than plywood.
    Really, I'm not missing the point. I just happen to think (from experience) that the beam I suggested would do the job without the corrosion of steel.

    The steel will work and that's probably what he should use. Be prepared for rust though.

    Has anyone calculated the loads on the beam in order to size it. That's where you should start. There is a book,by Harry Parker, SIMPLIFIED ENGINEERING FOR ARCHITECTS AND BUILDERS, available from Amazon. Spend a little time in that book, It is available from Amazon.
    Last edited by lowell holmes; 11-06-2015 at 12:49 PM.

  4. #34
    Quote Originally Posted by lowell holmes View Post
    I would probably use a piece of 1/2" exterior plywood. We used to make long beams in residential construction with two 2x12 boards with 1/2" plywood sandwiched. That gave us 3 1/2" in width, which fits standard 4" board widths and it is strong.
    Quote Originally Posted by Jamie Buxton View Post
    Yes, you should be okay. In fact, there might be a little advantage in holding the steel short of the beam ends. The steel may rust (if it ever rains in CA again). If the steel extends over the legs, rust stains might drip down the leg faces. But if the steel stops short of the legs, any rust drips would fall to the ground.

    interesting thought. I was reading about how flitch-plating was less optimal these days due to the fact that its more cost effective to sandwich marine ply which gives a similar strength and costs less ( and you can drive nails in)
    but for my application, I think steel is going to be the right route to take. thanks for the suggestion though! I did a cursory calculation on the sagulator and came up with an acceptable deflection result even without steel at a nominal load. I honestly think the steel is overkill, but I am a fan of overkilling it when underkilling it is a possibility.


    And thanks Jamie, thats kind of what I was thinking ... and I honestly think that 10 feet is way more than sufficient, but ive never done anything like this so ... have to ask!

    Wouldnt it be smart to coat the steel in some sort of krylon spray inhibitor or something prior to implanting it?

    thanks guys

  5. #35
    Thanks howie - this is definitely a mixed bag of heart and sapwood - probably all newgrowth. I am going to coat the leg ends with epoxy as suggested in an earlier post, give the whole thing a few good coats of spar and I will also instruct the customer to keep it covered with a tarp. I still like to reiterate that this will be in dry dry Los Angeles - and while we do have a stormy winter ahead, its rare and I take some solace in that fact.

  6. #36
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    Quote Originally Posted by Matteo Lorenzo View Post
    ...Wouldnt it be smart to coat the steel in some sort of krylon spray inhibitor or something prior to implanting it?...
    Yeah, trying to coat the steel would be a good idea. There are anti-corrosion paints, like Rustoleum. There's also truck-bed coating. Ugly, but strong, and it sticks to steel very well. You can buy spray cans of the stuff.

  7. #37
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    Yes, coating would be good. Any good metal primer.

    No adhesion necessary. Use plenty of screws. As a non-engineer, I would use something like a pair of screws every 12" or so.

    10' length should be fine.

    I'm surprised to hear that marine ply has a similar strength to plate steel. If you believe it, then use the ply.

  8. #38
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    Quote Originally Posted by Jerry Miner View Post
    Yes, coating would be good. Any good metal primer.

    I'm surprised to hear that marine ply has a similar strength to plate steel. If you believe it, then use the ply.
    Obviously marine ply does not have the same strength as steel. However, double 2X12 or for that matter 2X10 with 1/2" plywood between the 2X's has been used a long time and the resulting beam is strong. The beam with steel is stronger, but if the wood filler is strong enough, it is easier to use. It will rot, but it does not rust.

    It also is a beam design that has been around a long time.

  9. #39
    I just wanted to follow up and thank everyone involved in this thread for all of your insight and great ideas.

    I managed to finish the table without incident, delivered and installed today to a happy customer.

    For what its worth, I ended up going with the flitch-plated aprons that were doubled in thickness and connected to the legs with pegged double M/T. The connection is very rigid in the end and the table is really heavy and solid.

    For the flitch-plated apron side members, I routed an 1/8th pocket in each 4/4 piece of cypress and sandwiched the steel into that slot prior to glue/screw. I also used a fair bit of epoxy to really seat it in there.
    There is zero (noticeable) sag and I reckon that table could support a LOT of weight... the top will surely fail before the frame if there is a neighborhood dance party on it.

    so, again, thanks so much for everyone's participation. it was absolutely priceless to me.

    as promised, some snaps...

    resident butterfly that checked my work daily
    resting on a flitch-plated apron member after joining the two slats. 4in X .25in x 10ft plates embedded in both side apron members

    JtCHtrah.jpg

    double M/T connections to leg stocks. you can see the steel plate here as well

    H8a11Bjh.jpg

    angle showing the joined apron from leg to leg and no sign of sag. this was loadless, but I have put quite a bit of weight on the top to test and was not able to create any sag.
    it was probably overkill, in the end, but id rather that than underkill!
    YTMpfwKh.jpg

    and the finished piece at the new owners house

    Ru545RCh.jpg

    fSqmKhxh.jpg
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