Self forming fillets

Discussion in 'Fiberglass and Composite Boat Building' started by DogCavalry, Oct 14, 2020.

  1. DogCavalry
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    DogCavalry Senior Member

    So I had the notion, while making wet fillets, that I might be able to skip a step. I'm thinking of gently draping glass into an inside angle, and letting it settle at the radius it likes. Then after its cured, injecting in epoxy to fill the void. Anyone ever done this?
     
  2. fallguy
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    fallguy Senior Member

    Too costly and the epoxy will heat and leak out of any hole.

    My only regret filleting is using a radius that was a bit larger than really needed.

    I think the tongue presser I like is between 1/2" and 5/8". The 3/4" uses quite a bit more sauce.

    Also, cabosil is quite a bit cheaper, by volume.
     
  3. ondarvr
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    ondarvr Senior Member

    That would be more complicated than more traditional methods.
     
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  4. fallguy
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    fallguy Senior Member

    For you, filleting will be like nothing. Make sure and fillet same day you apply tapes; the bonds are much better. I think I calculated like 1 ounce of epoxy gave me 17" of fillet at 3/4". Eventually, you will batch expertly. Use my number for a start.

    Also, keep a smaller tongue presser around, because if you get to the end and you need 12" more fillet, you can usually step down to a smaller radius and avoid mixing more epoxy. I really never mix less than 3 ozs.
     
  5. DogCavalry
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    DogCavalry Senior Member

    I haven't found that cabosil bulked it up much at all.

    And in either case I have to drape the glass into the angle. But I take your point, Fallguy, about excessive volume getting hot. I've lost at least a liter or 2 with batches cooking off.
     
  6. DogCavalry
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    DogCavalry Senior Member

    My fillets are often larger than yours. For fillets at the transon in particular, I used a cylinder 1¼" in diameter.
     
  7. fallguy
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    fallguy Senior Member

    well, you didn't add enough cabosil!

    Use about 2+ to 1 by volume.

    ready for the accountant?

    I 10# bag of cabosil at $159 has approximately 5,250 cubic inches of material. For semantics, let's use 5000. This is the same as poured about 3000 liquid ounces. Roughly $0.053 per ounce.

    One gallon of epoxy at typical rates is about $1.00 per ounce. Let's say it is cheap at $0.80 per ounce.

    Using my 17" for one ounce and my 2:1 ratio; you'd need 1 oz epoxy and 2 oz cab or about $0.90 for 17".

    Using your method, you'd need 3 oz epoxy or $2.40. Cost is about 2.5 times more.

    I apologize.
     
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  8. fallguy
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    fallguy Senior Member

    that is 5/8" radius

    A 1.25" radius is too large..
     
  9. fallguy
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    fallguy Senior Member

    I forgot one aspect of the accounting for fillets. All of this has gone through my cost accountant brain while laying down a few thousand feet of fillets. Or at least a couple thousand...

    Weight.

    The weight of 3 liquid ounces of epoxy is about 0.211 pounds. Epoxy is heavier than water!

    The weight of 3000 (as poured) ounces of cabosil is 10 pounds, or 0.0033 pounds per volumetric ounce. Light like a feather.

    So, the by weight comparison for the same cost example of a 17" fillet is an all epoxy fillet weighs 0.211# and an epoxy cab fillet weighs 0.077#. So the cabosil option is also 2.7 times lighter.

    At that rate, 1000 feet of fillets weighs about 55 pounds with cabosil and about 148 pounds all epoxy. That is quite a bit.
     
  10. DogCavalry
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    DogCavalry Senior Member

    It seems, as I'm mixing, that 3 fluid oz of epoxy is 3.1 fluid oz after 6 oz of cabosil is mixed in. But I never measured.
     
  11. BlueBell
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    BlueBell Ahhhhh...

    John,
    What about your 1/4 round wood strips you were filleting with?
    Economical, light weight, easy application... did I miss anything?
     
  12. DogCavalry
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    DogCavalry Senior Member

    No, Bluebell. I used them, and they are cheap, and strong as hell. It was just an idle thought. I have a bunch of needles and syringes for injecting epoxy in some voids I have, that I picked up from Fibertek. It came to me that I could just as easily inject a lot of epoxy as a little. If I had more money than time, I would have a go at it.
     
  13. leaky
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    leaky Senior Member

    One boat builder I know, established business with a half dozen molds, recommends 1.5 inch fillets. Reasoning is they use standard 1.5 inch rollers.
     
  14. fallguy
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    fallguy Senior Member

    maybe final fairing, but not tabbing
     

  15. leaky
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    leaky Senior Member

    They use it on tabbing, basically how it came up in the first place is we were talking about bulkheads & stringers.

    In the same circle of builders another one tells me they never use a fillet, bah waste of time :)..
     
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