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#150627 - 05/21/11 01:17 PM Catenary Curves
TheNewGuy Offline
newbie

Registered: 05/05/11
Posts: 8
I've done some searching on catenary curves, and I'm wondering if anybody could explain, or link to a good explanation of how to set up a proper curve on a cat tarp?

Any help you could provide would be much appreciated.

Thanks!!

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#150629 - 05/21/11 03:50 PM Re: Catenary Curves [Re: TheNewGuy]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
I see you also asked at BPL so won't bother pointing you there. Several people have done spreadsheets. Here is one

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#150750 - 05/24/11 06:08 PM Re: Catenary Curves [Re: topshot]
Spock Offline
member

Registered: 01/10/06
Posts: 679
Loc: Central Texas
You don't have to put a cat curve in the ridge seam to get a tight set-up. Curves on the outside hems will do the same thing much easier. A one-inch offset for each foot of ridgeline will do the job. 1/2" grossgrain on the hems will prevent stretching of the hem on the bias, giving an even tighter set-up.

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#150753 - 05/24/11 07:45 PM Re: Catenary Curves [Re: Spock]
bmadau Offline
member

Registered: 09/14/05
Posts: 135
Originally Posted By Spock
You don't have to put a cat curve in the ridge seam to get a tight set-up. Curves on the outside hems will do the same thing much easier. A one-inch offset for each foot of ridgeline will do the job. 1/2" grossgrain on the hems will prevent stretching of the hem on the bias, giving an even tighter set-up.


I have a hypothesis going that getting a tarp good and taught is made more difficult because the hems don't stretch as much as the rest of the fabric. My proposed solution is to use a small zig-zag stitch on the hems and ridge-line, to allow them to stretch more (polyester thread doesn't stretch nearly as much as nylon fabric). I started a thread discussing this idea on bpl titled "Tarp Taughtness" if I recall correctly.

I have yet to test it yet, though... If it does truly work, it would be a lot easier to do than cat cuts.

BM

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#150811 - 05/26/11 01:17 PM Re: Catenary Curves [Re: bmadau]
Spock Offline
member

Registered: 01/10/06
Posts: 679
Loc: Central Texas
bmadau,
Sorry, you have it backwards; the hems stretch too much. The purpose of adding grossgrain to curved hems is to eliminate the stretch and to pull the stretch out of the bias of the fabric.

However, the zigzag is a good idea - especially if you are using polyester thread and don't use grossgrain reinforcement. As you noted, light Nylon fabric stretches a whole lot more than polyester thread and a strong pull will pop the thread like popcorn.


Edited by Spock (05/26/11 01:17 PM)

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#150867 - 05/28/11 12:52 AM Re: Catenary Curves [Re: TheNewGuy]
knosaj Offline
newbie

Registered: 09/19/10
Posts: 13
Loc: Tx
can someone point me to a thread or quickly explain this "grain orientation"

i was going to make my tarp by simply running the warp of the fabric with the length of the tarp. but there is little i hate more than a loosly pitched tent so i wanna make it right.

thanks in advance

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#151203 - 06/07/11 07:55 PM Re: Catenary Curves [Re: david5]
Kent W Offline
member

Registered: 10/15/09
Posts: 607
Loc: IL.
When making my cat tarp. I did not cat cut the ridge line. I did cat cut and double cat cut the edges. I am not sure if i am totaly positive on this, but it makes it pitch taught A frame style, or as a flat lean too pitch. This was my philosophy, and it seams to work well either way. I tacked my fabric to the wall and maked the cat cut with a sharpie. I did this with a piece of cord tacked as wall with the correct sag? Not rocket science, but it works? Excuse, my grammer, I have had a few after a very hot day at work! Good Luck


Edited by Kent W (06/07/11 07:57 PM)

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