1. ## caternary-cut edges

How do you get them? Is there an equation to figure out the depth or whatever and how do you pull of a cut like this on longer edges, say 3yds?

2. Rather than retype all of this, I'll just direct you to my opinion on the subject. There are several posts by me, I think the first and third have useful info.

HERE

3. Yep, Redoleary is all over it in that thread. A catenary curve is simply the shape of curve that is made when a string is hung between two points. Do it on a wall, trace it out and you're good to go. No equations required.

I remember once in college I had an assignment which required me to use calculus to figure out the area of a McDonalds M. That thing is made up of four sloping catenaries. Yuck!

I can tell you now, you don't want to be working with the equations!

4. I'm pretty sure I remember this right but a rule of thumb for the catenary cut is 1" of depth for every foot of length. So, let's say a hex tarp had 6' between tie outs then the curve would peak 6" in from the edge. What I've done is mark the peak of the curve on the material and then bend a dowel or some other flexible item so that it arches across the start and end points and the peak of the curve. Have someone hold it in place and trace the curve onto the fabric. No need to plot points mathematically.

5. I use the same method as Knotty, but sometimes don't have an extra set of hands to help hold things down. This is when a fiberglass tent pole and 2 C-clamps come in handy.
As far as measurements, I just move the pole up and down until it "looks about right". Hold the pole steady at the center and mark one side. Then carefully switch hands and mark the other side.

6. These guys are right.

Also, the catenary is the result of tension and weight. The curve depth which is most useful changes with those factors. If you want to get a nice headache, look up some write-ups on the term "catenary". That is why Knotty referenced the usual rule-of-thumb as to how much to apply.

Any curve will tend to tighten up a suspended, weighty item like a tarp. Too little curve for the weight results in a flappy tarp.