Glue Joint?

Discussion in 'Wood Construction' started by cdlwingnut, Mar 10, 2017.

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  1. Mar 10, 2017 #1

    cdlwingnut

    cdlwingnut

    cdlwingnut

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    I glued up some of the members of my fuselage and it looks like some of the t-88 ran out of the slight gap,
    how do you know if you have a good joint?
    and
    can you add more t-88 to an already glued joint that you aren't 100% sure of?
     
  2. Mar 10, 2017 #2

    Dana

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    There should be some squeezeout in a good joint, but there should be no gap once it's clamped. If you have a visible gap after the glue runs, not squeezes, out, I would think it should be redone unless it's a non critical area. It's sometimes possible to spread a gap of a broken joint just enough to squirt some epoxy in with a hypodermic needle and syringe (and then clamp it so most of it squeezes back out), but I wouldn't do it in a critical area.

    Dana
     
  3. Mar 11, 2017 #3

    Aerowerx

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    I've also had this happen.

    The problem I think is that there is a period in there, after the t88 is mixed, when it can get quite runny. Because it generates its own heat. I've mostly had this on vertical joints.

    Dana is right. You should not have a gap, but some squeeze-out. You also do not want too much clamping and squeeze out too much epoxy.

    Although it may not always be possible, keeping your joints horizontal as much as possible helps a lot
     
  4. Mar 11, 2017 #4

    lr27

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    IF you are going to fill gaps, there's a narrow window in which to do it. After that, you don't get the chemical bond you would if the original epoxy isn't fully cured. Or so I've always read. And if you have conditions that allow blushing to occur, that's another complication.

    Is it kosher to use a small amount of some thixotropic element? Cotton flox? Fumed silica? (I'm guessing the latter would stiffen it up too much.)
     
  5. Mar 11, 2017 #5

    RUSTY

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    End grain glue joints have virtually zero strength. The only reason to glue those joints is to keep all the bits stuck to all the other bits while you remove it from the jig. There are two reasons to have nice tight fitting joints.
    1. Pride in workmanship
    2. Epoxy is heavier than wood
     
  6. Mar 11, 2017 #6

    FritzW

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    Can you post some pictures of the area in question? How big is the gap, how deep?
     
  7. Mar 11, 2017 #7

    Rockiedog2

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    like Dana said squeezeout is desirable. that indicates a joint that isn't glue starved adn also adequate clamp pressure. i agree with aerowerx when he recommended horizontal joints as much as possible while gluing and setup; it will tend to run out of the joint if vertical. in my experience, a spring type is the wrong clamp...it will apply continuous pressure til past the desired amount and we get too much squeezeout and a possible starved joint. i use a screw type clamp and tighten it til i get squeezeout most all round; let it sit a few minutes then go back and tighten it just a little more. then leave it alone overnight. destructive testing on test joints will give the experience to make a proper judgement on the right technique. T88 really isn't very critical once you get the feel of it.
     
  8. Mar 11, 2017 #8

    cdlwingnut

    cdlwingnut

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    20170310_103448_resized.jpg 20170310_103436_resized.jpg

    these are the ones concerning me
     
  9. Mar 11, 2017 #9

    DaveD

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    Those all look like end grain joints which have minimal strength. Adhesives transfer way more load in shear, so I guess all of the joints shown will get gussets added which will actually carry the load. In that case I wouldn't worry about the gaps as long as the gussets are soundly glued with no gaps.
     
    delta likes this.
  10. Mar 11, 2017 #10

    FritzW

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    Those joints don't need to (and won't) carry any shear loads. I'd fill them to keep water and dirt out but I don't think they're anything to worry about. Just make sure the ply that goes over them is glued down properly.

    Are all the pieces the same thickness? (hard to tell in the photo) The ply obviously needs a good flat surface to glue to.
     
  11. Mar 11, 2017 #11

    cdlwingnut

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    yes all the pieces are 3/4" thick and a sheet of plywood goes over them.
     
  12. Mar 11, 2017 #12

    Aerowerx

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    What plane is that? Looks like a Ragwing. Of course a lot of the "cheaper" designs are copies (or near copies) of each other.

    These are the type of clamp I like to use:
    038548103709.jpg
    They come in different sizes, and I have a bunch of 6 inch ones. They are easy to adjust to get just the right amount of pressure.
     
  13. Mar 11, 2017 #13

    Rockiedog2

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    so a gusset or panel goes over the joint which, like the others said, takes care of the concern. The thing I don't like doing is gluing on top of T88 like where it squeezed out of your joint, reason being that the area didn't have any clamp pressure on it as it setup and there likely isn't penetration which we all know is the heart of the strength of the joint. I've talked to T88 tech about it and they say it's ok if the squeezeout is flat like with a file and the gloss is gotten off of it, or just wipe it off when gluing then rough it up for the new glue to adhere to. I still don't like doing it but it can't be helped sometimes. I'm not advocating this at all of course with those joints of yours but just a point of info...my old set of Pitts plans show the rib diagonals not even shaped to fit the joint; just cut off square and the gusset takes all the load.
    That area you're talking about looks like it may be where the tailwheel mounts is that right? if so that area takes a beating
    I use those type clamps that Aerowerx uses too. Harbor Freight has some little ones that are really handy and cost nearly nothing. bout a 2-3" range.
     
  14. Mar 11, 2017 #14

    cdlwingnut

    cdlwingnut

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    yes this is a ragwing ultra-piet, and the joints in question are under where the seat will be
     
  15. Mar 11, 2017 #15

    Tcreek

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    T88 also has an epoxy gel that works great for vertical glue joints. When warm
    it has the consistency of honey after mixing. I have been using it lately
    and have had good results.
     
  16. Mar 11, 2017 #16

    BBerson

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    Small, tight fit corner blocking can hold the glue in. Why not glue the whole thing with gussets in one step?
     
  17. Mar 11, 2017 #17

    Dana

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    I would file down any existing squeezeout flush with the wood, then use a syringe to squirt epoxy into the gap at the same time as you glue the gussets in place.

    Dana
     
  18. Mar 11, 2017 #18

    pictsidhe

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    Harbor freight often has their little clamps as free with voucher. I pull up http://www.hfqpdb.com fora list of all current vouchers and show them on my phone. Last I looked, they had some no purchase required vouchers.
     
  19. Mar 11, 2017 #19

    Aerowerx

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    I believe it says on the System Three web site that T88 will bond to itself.

    As far as kosher, talk to a Rabi. But flox is usually used to fill gaps that can't be avoided otherwise. Flox is structural, IIRC, while beads are used to smooth surfaces.
     
  20. Mar 11, 2017 #20

    TJay

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    I was wondering about adding flox to t-88 It should work fine, I used alot of flox on my kitfox build, using an epoxy glue
     

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