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Thread: Glue joints

  1. #11
    iflypa28's Avatar
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    I have noticed that you can't use much clamping pressure. I built a jig for the fuselage sides so I wouldn't have to use clamps. What is everyone's experience with using a staple gun for the gussets with epoxy, does this apply to much pressure and squeeze the glue out? Is there a better way?

  2. #12
    cub builder's Avatar
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    I would suggest you look at some of the many KR sites. They are built with the same wood stick and gusset framing with plywood shear webbing. You'll learn a lot about acceptable methods and techniques on their sites.

  3. #13

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    Quote Originally Posted by iflypa28 View Post
    What is everyone's experience with using a staple gun for the gussets with epoxy, does this apply to much pressure and squeeze the glue out? Is there a better way?
    staples work, use caution because they will split the wood and if you staple through a strip of cardboard you can remove the staple after the glue dries. The staples will only rust anyway.

  4. #14
    bigdog's Avatar
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    Quote Originally Posted by iflypa28 View Post
    What is everyone's experience with using a staple gun for the gussets with epoxy, does this apply to much pressure and squeeze the glue out?
    I built a set of ribs for an L-2 restoration project and I got some good advice on the Biplane Forum. I used a pneumatic Senco stapler and SS staples. You need to adjust it so the staple sits flush on the gusset but doesn't crush the fibers. To adjust it, depress the trigger and grind off the plunger until the staples sit where you want them. With SS staples you can leave them in. The stapler makes it easy and quick. Well worth the money spent.
    Regards,
    Greg Young
    1950 Navion N5221K
    RV-6 N6GY - waiting for AWC inspection
    1940 Rearwin Cloudster is next
    4 L-2 projects on deck

  5. #15

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    To the OP,

    I think you may be misinterpreting that 'wood breaks before the glue' premise. The premise doesn't mean that the entire stick of wood will break.

    If you look closely at your test joint, you'll see wood fiber from the top of the 'T' adhered to the end grain of the leg of the 'T'. That is your evidence that the wood failed before the glue. What you're really seeing (as others hinted) is stressing a joint outside its design, and I don't mean overstress; I mean that the joint isn't designed to be stressed in the direction/angle you're stressing it.

    I'm not an engineer, so I don't feel qualified to give a tutorial on it, but here are some starting points to see how to design joints.
    https://www.masterbond.com/techtips/...hesive-bonding

    https://www.google.com/search?q=glue...hrome&ie=UTF-8

  6. #16

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    Quote Originally Posted by rv7charlie View Post
    To the OP,

    If you look closely at your test joint, you'll see wood fiber from the top of the 'T' adhered to the end grain of the leg of the 'T'. That is your evidence that the wood failed before the glue.
    I agree. The glue joint is perfectly acceptable. The wood failed before the glue. If you have gussets to hold the two pieces together then the glue between the two pieces is mute. The strength is in the gusset. On my wing I had one butt joint that didn't have gussets. The aileron spar butts up against the rib. While not called for in the plans, I used a couple of dowels to tie the pieces together.

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    The other question about sanding. I used birch plywood for my rib gussets. The plywood is shiny smooth. I used 80 grit sandpaper to rough up the surface of the plywood so the glue had something to adhere to. A lot of people use plexiglas for the rib jig. The secret there is the shiny smooth surface of the plexiglas. T-88 sticks but not well and can be easily removed. Rough up the plexiglas surface (from multiple uses) and you'll start to have a difficult time cleaning off the glue.

    You only need to use staples if you are going to pull the rib out of the jig before the glue is set. You can make multiple ribs in a day that way. You can staple through cardboard and remove the staples once the glue is set. The cardboard is so you don't mar the surface of the gusset. You can also leave the staples but they just add weight.

    I made one rib a day in the jig and left it overnight for the glue to set. The next day I flipped it over, added the gussets on the other side and made a new rib in the jig. That way I had plenty of time to coffee with the locals when they showed up to critique.

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    http://myhatz.blogspot.ca/

  7. #17

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    Quote Originally Posted by iflypa28 View Post
    I have noticed that you can't use much clamping pressure. I built a jig for the fuselage sides so I wouldn't have to use clamps. What is everyone's experience with using a staple gun for the gussets with epoxy, does this apply to much pressure and squeeze the glue out? Is there a better way?

    Suggest research on technique vs glue type. IIRC, older glues like resorcinol require near perfect fitment, so that there is almost no glue gap, and significant clamping pressure, while others, like T-88, are much more tolerant of gaps. It would pay to read up on the proper technique for your glue of choice. The resorcinol glues are stronger than the wood, but require better technique to develop that strength, but can have an advantage over many epoxies when it comes to environmental properties.

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