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Thread: Making Cat Cuts

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  1. #1
    Ramblinrev's Avatar
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    Making Cat Cuts

    Is there a difference between a cat cut and a parabolic cut? For example the Blackcat tarp lists specific easurements which make the cat cut. The dual mode bridge suspension cut is traced from a tent pole or some such. Is there a reason I should not do a cat cut tarp the trace a tent pole style or do I really need to do the measuring?
    I may be slow... But I sure am gimpy.

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    Mule's Avatar
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    I think either way would work as long as the tent pole bends evenly. Another way to get a cat cut as explained by someone on this forum is to hang your material on the wall and pin a cord across it, letting it hang at the desired distance from the edges to the depth of the arc. Then mark the hang of the string on the fabric. Sounds like a good plan to me, and I suspect this is the way the measurements came into being. Mule
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  3. #3
    Senior Member te-wa's Avatar
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    catenary arc is described as the arc formed by a chain suspended at two points. SO, get some ball chain from the hardware store and hang it on the wall. Done!

  4. #4
    Oh-No's Avatar
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    Quote Originally Posted by Ramblinrev View Post
    Is there a difference between a cat cut and a parabolic cut?
    Yes, cat cut (as we use the term) is shorthand for cutting a piece of cloth along a catenary curve.

    Catenary curve- Take a flexible chain of uniform linear mass density. Suspend it from the two ends. The curve is called a catenary.

    It is different from a Parabolic Curve which is the curve formed by the cables of a suspension bridge.

    For a better and more complete discussion go here:

    http://whistleralley.com/hanging/hanging.htm

    After reading a bit, and with my limited understanding of it all, my guess is that for tarps and bridge hammocks, it is better to use a parabolic curve,
    although for our purposes the difference between using a cat curve and a parabolic curve may be inconsequential.

    If my guess is wrong, someone please chime in and educate me. My ignorance is vast and my suppositions not always correct.

  5. #5
    GrizzlyAdams's Avatar
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    Quote Originally Posted by Ramblinrev View Post
    Is there a difference between a cat cut and a parabolic cut? For example the Blackcat tarp lists specific easurements which make the cat cut. The dual mode bridge suspension cut is traced from a tent pole or some such. Is there a reason I should not do a cat cut tarp the trace a tent pole style or do I really need to do the measuring?
    Being a quant and not a little pedantic, the figures in the dual mode guide come from the equation for a parabola. The pedantic part comes in because I think that for the bridge suspension---and a tarp for that matter---this is technically the proper shape.

    That said, I don't think it matters a whit on the bridge suspension. The flexing pole method works fine and is most definitely NOT a parabola NOR a catenary curve.

    You can write (my cause, program) the equation for a parabola using ordinary algebra from the desired length and depth of the curve. For a cat curve, to get the coefficients needed for the equation you need to set up a function involving hyperbolic sine and cosine functions, and solve them numerically. 'nuff said.

    Grizz

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    Ramblinrev's Avatar
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    So is this a loose but essentially accurate translation of "grizz speak"...

    "Whatever... There is a technical difference but who gives a whiz when it comes to camping gear. Use a tent pole if that's the way your mind works...." ... ?
    I may be slow... But I sure am gimpy.

    "Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
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  7. #7
    GrizzlyAdams's Avatar
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    <grizz speak>
    that's about right.
    </grizz speak>

    Grizz

  8. #8
    Senior Member stoikurt's Avatar
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    Quote Originally Posted by Ramblinrev View Post
    So is this a loose but essentially accurate translation of "grizz speak"...

    "Whatever... There is a technical difference but who gives a whiz when it comes to camping gear. Use a tent pole if that's the way your mind works...." ... ?
    Nice translation!
    Stoikurt
    "Work to Live...Don't Live to Work!"

  9. #9
    GrizzlyAdams's Avatar
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    good to have you posting again Stoikurt, even if it's translation commentary

    Grizz

  10. #10
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    Oh man another cat vs parabolic vs the bent stick talk. When it comes down to it, I think the sewing, cutting, measuring, drawing, my head on a tilt, and the gravatational pull on the moon errors introduced into the mix cause all the fine differences not to matter.
    Is that too much to ask? Girls with frikkin' lasers on their heads?
    The hanger formly known as "hammock engineer".

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