DIY Epoxy Weight/Balance Scale

Discussion in 'Workshop Tips and Secrets / Tools' started by Aerowerx, May 28, 2016.

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  1. Feb 4, 2017 #21

    Aerowerx

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    Keep in mind that the manufacturer recommends mixing by weight as the preferred method.

    What I found was that there was a discrepancy in their data sheet for T88---the properties of T88 disagreed with the mixing (by weight) ratio, but I could not get them to admit to it. Of course, at the time their technical people where at a convention, and the person that answered their email was just saying what she was told.
     
  2. Feb 4, 2017 #22

    Little Scrapper

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    You couldn't get them to admit what? The little bit it's off is irrelevant to the strength, that's the beauty of T88, it doesn't need to be perfect in the way you deem perfect. Even mixed inaccurate the strength probably exceeds the requirements.
     
  3. Feb 4, 2017 #23

    Tiger Tim

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    That's the as-yet-unpublished final chapter of this all, isn't it? Both sides of this thread are all theory (and both are good enough) until someone does extensive strength testing of by-weight and by-volume mixes then compares the results to what we're supposed to expect from the stuff.
     
  4. Feb 4, 2017 #24

    BJC

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  5. Feb 4, 2017 #25

    Little Scrapper

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    I'd rather build than spend time trying to figure out a problem that doesn't exist, I mean that in a nice way, not trying to be a jerk.

    T88 is used globally right? The company itself has a lab I bet. Some of the greatest airplanes that exist use T88.

    Where's the real problem? Show me the actual problem? I admire the quest for perfection but there's limits to this right?
     
  6. Feb 4, 2017 #26

    Pops

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    I use a balance beam that I made for an ounce or more, under that, I just squeeze out two equal size puddles and mix. No big deal. Make glue samples and break and you will see the wood will fail first.
     
  7. Feb 4, 2017 #27

    TFF

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    Like all things the mixing tube has its place. Where it exceeds is speed and accuracy. It will be tool of choice for ply skin installation. Trying to not make a mess when you have a 4x8 piece of ply and are trying to get the glue on the ribs, especially when closing a wing is worth $6. Otherwise big bottles is the way to go for economy.
     
  8. Feb 4, 2017 #28

    Little Scrapper

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    Exactly. If if mixed wrong the material breaks begore the epoxy does.
     
  9. Feb 4, 2017 #29

    Aerowerx

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    Whether you mix by weight or volume should not matter as to the end results.

    But either way you should be using both parts at the same rate. When using their weight ratio I found that I was using the resin (IIRC) faster, therefore I was having to buy more sooner than expected. After I found the error in the data sheet the problem went away.

    Has anyone else considered that viewpoint?

    If you measure by weight or volume probably doesn't matter as much as how sloppy you are in the measurements, but if using weight I highly recommend NOT using their ratio, but the ratio of the specific gravities.
     
  10. Feb 4, 2017 #30

    Little Scrapper

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    Yeah, I think many can see that viewpoint. It just doesn't matter to a bunch of people because we just order more. I think it depends on the quantity used and the airplane your building. I just use it on ribs so if one runs out before the other so what, I have extra that ill never use anyhow. In fact, I just threw out a big tube that was 3/4 full because it sat for 2 years.

    If you use a lot of T88 I can see where your point is valid.
     
  11. Feb 5, 2017 #31

    Aerowerx

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    You just wasted some T88, LS!
     
  12. Feb 5, 2017 #32

    Little Scrapper

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    I just don't trust it from sitting. I don't mind spending the little bit extra for a fresh tube.
     
  13. Feb 5, 2017 #33

    lr27

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    I bet they don't work well in the crystallized state unless reheated to redisolve. In the summer, it's easy. Just leave it in your car in the sun for a couple of hours.

    Seems like it would be easy to test the stuff if tested the strength of the bond when it was new and then tested in exactly the same way before using. Ideally, two small plates with rings to tug in something that didn't have surface prep issues, but was stronger than the glue. Off the top of my head, I'm not sure what that material is. Maybe hardwood end grain??? Of course, no two pieces are exactly identical. It's hard to be consistent with surface prep on metals.
     
  14. Feb 5, 2017 #34

    Aerowerx

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    I have had some that had started to crystallize.

    The crystals dissolved as soon as you mix. Remember it will generate its own heat when curing.
     
  15. Feb 5, 2017 #35

    TFF

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    I would not be laminating spars or critical with old. T-88 writes the rules for boats, not quite for airplanes. I keep the old around for model airplanes and maybe blocking or non critical. I dont throw it out, but it changes use.
     
  16. Feb 5, 2017 #36

    lr27

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    I usually manage to get epoxy in place without much self-heating going on. My experience with larger batches and self-heating is that if it's significant, you run out of time to use the stuff before it gets too awful to use. I'll admit I haven't tried mixing to see if the crystals go away, but then it's quite easy to get rid of them entirely ahead of time.
     

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