Vertical bonding joints.

Discussion in 'Wood Construction' started by Tantrum1, Aug 15, 2018.

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  1. Jul 4, 2019 #21

    Aerowerx

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    Sorry, BJC. I should have been more clear. I was not commenting on YOUR post, but on all the others that you were commenting on. I read yours as a summation of my thoughts.

    I just find it amusing, all the back and forth discussion on whatever topic by the 'experts', but no one suggests checking with the REAL authorities---those who make the stuff. Which is what I did. If and when I ever continue with my build I will go by what is suggested by System Three and use Cabosil.
     
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  2. Jul 4, 2019 #22

    TFF

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    In the real world, no one checks with experts. No need for forums then.
     
  3. Jul 4, 2019 #23

    Victor Bravo

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    Speaking only for myself, I purposely used Rutan as a subject matter expert, since his involvement was far more homebuilt airplane-specific than the System Three people, who are thinking globally about any and all uses for epoxy.
     
  4. Jul 4, 2019 #24

    Rockiedog2

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    yeh you can call System 3 or whoever it is and see what they say but you still need to experiment to gain the personal experience to make the judgement call required when gluing up anything critical. Discussions on forums are ok but nothing takes the place of personal experience and there's only one way to get that. Homebuilding wood airplane parts has always been based on test samples etc for the inexperienced as well as the ones who been there before.
    So go ahead and beat it to death here on the forum long as you want that's common but you still gotta experiment with it. In the time already spent here several test samples of varying density could have been glued up and the OP would have his *real* answer.
     
  5. Jul 4, 2019 #25

    cavelamb

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    since no one has said it...

    The three viscosities I use are 1) maple syrup. 2) mayonnaise, 3) peanut butter.

    In your example mayonnaise should work well
     
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  6. Jul 6, 2019 #26

    MadProfessor8138

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    This is the reason that I love and also hate forums in general.
    Yes,I realize that the manufacturer SHOULD HAVE any answer that you could possibly ask a question of....but it doesn't always work that way.
    The lab guys work in controlled environments under controlled conditions to base their answers upon....that's not how the real world works.
    I would take the opinion of the grizzled old fabricator that can tell me what works and what doesn't work over some pencil pushing geek anyday.
    My apologies to any pencil pushing geeks out there.....lol
    You get my point though....

    And I plan to do some test samples once I obtain the material to do so......but for now,I merely asked to get everyone's opinion as to what has worked for them.

    Kevin
     
  7. Jul 6, 2019 #27

    Kamcoman77

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    I have built a wooden KR-2 and am building a wooden wing Legal Eagle XL. If you use a syrup or mayonnaise consistency epoxy/Cabosil mix, you normally won't have to worry about penetration. If you are concerned about penetration when using a peanut butter consistency epoxy/Cabosil mix, mix a small amount of regular T-88, and in a separate container, your normal amount of thickened T-88. Using a stiff brush (bristles cut half off of acid brush), apply a small amount of regular T-88 to your joints, just enough to penetrate the wood (scrape off all excess with brush or plastic squeegee). Then apply your thick mix sparingly. I have used this to bond 1/4" wide vertical ribs to a spar or 5/8" verticals to a fuselage side with excellent results. You might waste a little epoxy, but you will not get any starved joints.
     
  8. Jul 6, 2019 #28

    BJC

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    K77

    That is a good technique tip.


    BJC
     
  9. Jul 7, 2019 #29

    Rockiedog2

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    Relevant to the starved joints question is gluing pressure techniques. Some use weights when the work is horizontal and some use spring clamps or clothes line clamps. Both those techniques apply constantly increasing pressure that will continue to squeeze the glue outa the joint til it gets too stiff. Maybe it'll come out right but that's a little iffy IMO. I rarely use either but use staples and set them fully with a tack hammer and pull em out the next day. From experience, I know that works for me. Good penetration and proper squeezout all round the gusset or whatever it is we're gluing. And once the pressure is set it stops squeezing the glue out. I want my glue joints visible; say about 10 or 15 thou or so. Well, never have miced it but my eye knows. And how did my eye get to know; by experimenting and doing many test samples and destruct testing.
     
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  10. Jul 8, 2019 #30

    MadProfessor8138

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    There are those times were staples are not an option though......
    I laminated the 2 elevator sections for my RW19 Stork in the past few days and the only way to do that is by using clamps to hold the laminated strips together.
    For just about everything else,yes staples are the technique that I use also.

    Since Rockiedog2 mentioned the topic...
    I had a few guys stop by the shop today to check out my progress and then "THE DISCUSSION" ensued.
    Everyone thought progress was going well and everything looked good....then "The Comment" was made by "1" individual that my joints were too big....everyone else thought they looked fine though...and I think they look fine myself.
    I tried to explain to the individual that if you have a joint that is a 100% perfect fit then you are going to have weak joints from glue starvation.
    T88 is an epoxy and has good gap filling properties compared to the old glues that were once used that did require a perfect joint fit.
    All of my joints have been "relaxed" just a tad for glue retention.
    Not to hijack the thread,but,I will post a few picks tomorrow and get some opinions on the subject.

    Kevin
     
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  11. Jul 8, 2019 #31

    Aerowerx

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    As a side note to this discussion, System Three recommends measuring by weight, particularly for small batches. Measure by volume is not precise enough, they say.

    If you go to all the trouble making a nice precise glue joint, shouldn't you apply the same care to the epoxy mix itself?

    I posted on this several years ago, and got jumped on by some who thought I was being too picky. There is an error in their data sheet for T-88. Do not use the listed weight ratio. Instead use the ratio of the specific gravities of each component. (pointed this out to System Three, but they didn't understand what I was getting at) Instead of weighing each component, build a simple balance beam scale. Instructions to anyone that's interested---just ask.
     
  12. Jul 8, 2019 #32

    TFF

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    If you want to be precise, measure out equal cc’s then weigh. If I had 6 joints to make, I would squeeze into 6 mixing cups, one for each joint. Do what you want to measure as T 88 is designed for the novice, not the expert. Legacy formula designed for ease of use. System Three bought the company that originally made it.
     
  13. Jul 8, 2019 #33

    Aerowerx

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    Which is how I discovered the error in the data sheet! The weight of equal cc did not match the ratio given in the data sheet.
     
  14. Jul 8, 2019 #34

    Rockiedog2

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    sure you can be as precise with it as you want but it's not necessary. I've glued up countless joints and also destruct tested countless as well(since the early 70's) and I've never measured other than by volume. The only joints I've had that didn't tear wood were ones that I failed to remove the wax from the plywood gussets. In my experience, that's the most important prep step of all.
    I think the lawyers got in on writing the directions.
     
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  15. Jul 9, 2019 #35

    wsimpso1

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    Glass fiber resin retention is smaller - no texture on each fiber and no absorption. Glass fibers are denser too. In total, any volume of flox will hold resin better and weigh less than cat fur.

    The best is cabosil (fumed silica)for keeping resin in joints. Big gel effect with least amount in the resin.

    Billski
     
  16. Jul 10, 2019 #36

    MadProfessor8138

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    So here are some of my glue joints.......
    Opinions.......too loose,too tight or alright?
    Glue is T88....
    20190709_191050.jpg

    20190709_191008.jpg

    Kevin
     
  17. Jul 10, 2019 #37

    Rockiedog2

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    dunno the dimensions in that pic so hard to guess. That widest area in the corner of the upper pic. Is that about like a spark plug gap? like about 25 or 30 thou? It looks like more glue pressure would have tightened it up; do those joints get a gusset? I looked back at a couple pics of mine and they're tighter. That doesn't mean yours won't hold up especially if they get a gusset. Is that in the corner of a rib?
    Not a good answer but best I can do from the pics. The answer is in the destruct tests you do on similar joints.
    BTW, I got joints with the grain square like yours too, everybody does but given a choice I like mine turned 45* especially if it's in a spar member. I don't care in gusseted rib joints.
    The old Weldwood plastic resin and rescorinol(sp) needed near perfect joints; not forgiving and no longer recommended and there's still wings out there glued up with it and still flying. Those best joints aren't as good as the average T88 joint.
     
  18. Jul 10, 2019 #38

    MadProfessor8138

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    It's hard to tell the dimensions from the pic but the joints look much bigger in the pic than they are in real life.
    If I was to throw my plug feeler gauges to them they would come up around .010-.015...
    Those are actually corner blocks on the stick built fuselage sides that will be sheeted with 4x8 sheets of ply.
    That's why I'm not too concerned with those joints......the entire fuse side will be sheeted and the ply will take the stress.
    I'm attaching a pic from the plans and you can see where those blocks are positioned if you look carefully....9 in total
    20190709_210133.jpg

    20190709_205152.jpg

    Kevin
     
    Last edited: Jul 10, 2019

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