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  1. #1
    Senior Member Patrick's Avatar
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    How do you cat hem cuben?

    I watched Sgt. Rock's excellent video on the cuben tarp construction, which uses flat seams. I'd like to make one with cat sides.

    I'm concerned about bunching when hemming. When I've made sil tarps, any minor wrinkles were hidden under the grosgrain trim. Looks like no such luck with folding over the cuben.

    Is there a way of hemming along the curve smoothly? I'm hoping I can just press it tightly as I go and generally be careful, but I want to be sure. I'm picky and it's not cheap stuff.

  2. #2
    WV's Avatar
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    When I first made my 9' x 11' cuben tarp, using CT.6K.08 material, I folded the straight edges over 1/2" and taped them down with 3M adhesive transfer tape. This made a strong edge, and it was easy to do. Last year I decided to try adding catenary cuts to the tarp edges, so I marked the curves by tracing along a masonite form. Then I put blue masking tape along the line and painted a 1/2" wide section along the outside of the line with 3M primer 94. Then I put 1/4" wide 9460 adhesive transfer tape down 1/4" outside the marked line, so when I folded it in it would adhere to the other half of the primed 1/2" wide stripe. The craft paper backing of the tape makes it easy to fold to the line. Then, holding the fold down with one hand, I pulled the craft paper backing out from between the two layers of cuben, leaving the adhesive between them. They instantly bonded to each other because they were already in contact. The narrow tape made it easier to follow the catenary curve. This 1/4" wide hem has held up just fine through some pretty rough weather in the last year.

    You could sew a hem, also. It might not be as strong as a bonded hem, but I think it would be plenty strong enough. I'd use a single fold 1/4" wide. Try ironing the fold in first, but don't use a hot iron. The Dyneema fibers have a very low melting point - much lower than that of the polyester film they're laminated in.

    Here are some still photos of the first part of the operation. I have raw video showing more, which I'll try to upload tomorrow.
    Attached Images Attached Images

  3. #3
    Senior Member Patrick's Avatar
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    Thanks, WV. I appreciate the thorough reply.

    Just to be clear, the wrinkling I'm worried about isn't just the act of folding a narrow sticky edge over. What I mean is the inherent inability of the curved edge to fold completely flat. Like if you were to cut slits in the part to be folded over, they would open up as it was folded back into a curve. Am I being clear as mud?

    That said, it sounds and looks like maybe the amount of wrinkling here is somewhat theoretical. Is it just the case that the curve is gradual enough and the material forgiving enough that a careful hand will produce a flat hem and I'm worrying over nothing?

    What about grosgrain trim along the hem either sewn or bonded? I've had good luck with that on sil tarps. Will that have the same benefits on cuben fiber or is the stitching actually subtracting strength?

  4. #4
    Ramblinrev's Avatar
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    I do not use cuben so take that into consideration. The rule of thumb is the smaller the fold the less wrinkling will occur with the fold. So a 1/16" fold will wrinkle less than a 1/2" fold will wrinkle less than a 3" fold. By the same token a cut of 1" depth will fold smoother than a cat cut of 6" depth. So you best best bet, fusing or stitching would be to experiment with the variables and find what works best.

    In "sewing" (as opposed to gear making) we will slash the curves before we stitch them down. Mark the fold line carefully and cut to within 1/16-1/8" of the line. The tiny fold will then be easier to make flat while the slashes will separate or overlap as needed to ease the curve. That works very well with woven fabrics. How well it would work in a non-woven I don't know. But the theory should apply. I would encourage a fused hem if you wanted to try that.
    I may be slow... But I sure am gimpy.

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  5. #5
    Senior Member lustreking's Avatar
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    Disclaimer: I don't have any Cuben stuff.

    Question: Since there isn't any stretch to cuben, are cat cuts necessary?

  6. #6
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    Quote Originally Posted by lustreking View Post
    Disclaimer: I don't have any Cuben stuff.

    Question: Since there isn't any stretch to cuben, are cat cuts necessary?
    When I make my cuben in a week or so I am going to put in some cat cuts. However, they're only going to be about 2-3" deep and will mainly be there to help in case I get into some strong winds. Which happens to me more often than I want.

    Fronkey

  7. #7
    WV's Avatar
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