# Thread: How To Make Perfect Catcuts On A Tarp

1. excellent idea, making a bow like that. The curve is not catenary or parabolic but the deviations from those mathematical ideals are within the level of accuracy that most of us can sew.

The idea has application to tracing suspension curves on bridge hammocks, at least if you can bend the pipe to have a 6-8" depth from the midpoint to the bowstring.

thanks for posting this.

excellent idea, making a bow like that. The curve is not catenary or parabolic but the deviations from those mathematical ideals are within the level of accuracy that most of us can sew.

The idea has application to tracing suspension curves on bridge hammocks, at least if you can bend the pipe to have a 6-8" depth from the midpoint to the bowstring.

thanks for posting this.
Thank you, GrizzlyAdams. Your absolutely right that it's not a true parabolic, and I guess this can be called a "fast and dirty" method, but using a long pipe will allow you to make a "better" curve that's more parabolic - although not a true curve - and I should have made the effort to better explain this in the thread.

After making a few tarps using this method, I find the depth of the curve to be important for making a taut pitch. For those starting a tarp for the first time, its quite intimidating working with catcuts and I admit it's not perfect, but it will get you in the ballpark.

So, I apologize for listing the title as "perfect curves". One thing that the pipe method does do is make the catcuts on both sides more consistent, although they're not true curves. My plastic pipe at 10' long can be bent to make curves with a depth of 4 or more feet - it's what I use to make the dory boat curve on my hammock socks. Me and math don't get along that well anymore, , hence the plastic water pipe to help me along!

Cutting out cardboard templates that have a true parabolic curve would be a better solution and be more accurate.

3. ## Re: How To Make Perfect Catcuts On A Tarp

Originally Posted by lokbot
that's a pretty good idea. that pipe looks like it's flexing point isn't truly parabolic, but I'm sure this will get you close enough. I'm still a sucker for plotting measurements with a ruler on a large piece of card stock.

-Loki
Am I missing something? This is just so it won't flap in the wind...... Right? Or is there something more? Sorry, I'm just failing to see the need for such precision that is so often used for cat cuts. I use a similar method as lost biker, and I would say you would be hard pressed to see the difference after the rolled hem..... IMHO

4. Originally Posted by Lost_Biker
Thank you, GrizzlyAdams. Your absolutely right that it's not a true parabolic, and I guess this can be called a "fast and dirty" method, but using a long pipe will allow you to make a "better" curve that's more parabolic - although not a true curve - and I should have made the effort to better explain this in the thread.

After making a few tarps using this method, I find the depth of the curve to be important for making a taut pitch. For those starting a tarp for the first time, its quite intimidating working with catcuts and I admit it's not perfect, but it will get you in the ballpark.

So, I apologize for listing the title as "perfect curves". One thing that the pipe method does do is make the catcuts on both sides more consistent, although they're not true curves. My plastic pipe at 10' long can be bent to make curves with a depth of 4 or more feet - it's what I use to make the dory boat curve on my hammock socks. Me and math don't get along that well anymore, , hence the plastic water pipe to help me along!

Cutting out cardboard templates that have a true parabolic curve would be a better solution and be more accurate.
Willing to bet it is pretty close to a parabolic curve. It should get the job done pretty good. This is how I did my first tarp but with tent poles instead of pvc...This looks to be a pretty cheap and super easy method that almost anybody can utilize. Thanks for sharing.

5. Fiberglass tent poles and three 1 gallon paint cans. Use two to set the ends and the third to push the pole centers into position. That's real down and dirty.

6. Originally Posted by Fireline
Am I missing something? This is just so it won't flap in the wind...... Right? Or is there something more? Sorry, I'm just failing to see the need for such precision that is so often used for cat cuts. I use a similar method as lost biker, and I would say you would be hard pressed to see the difference after the rolled hem..... IMHO
No, your not missing anything. It's for a taut pitch so it won't flap in the wind.
It doesn't hurt to be precise, but the pipe method makes it faster at the cost of being a little less precise. I can't really tell the difference between a tarp made either way either. I just wanted to clear up the title of the thread - the cuts are not perfect curves - just kinda close. I should be better at explaining things. What I meant to say is that the curves are more consistent, easier to trace and is faster working with the pvc pipe

Originally Posted by XTrekker
Willing to bet it is pretty close to a parabolic curve. It should get the job done pretty good. This is how I did my first tarp but with tent poles instead of pvc...This looks to be a pretty cheap and super easy method that almost anybody can utilize. Thanks for sharing.
Your welcome, XTrekker. I need to find the time and see just how far off the pvc pipe curve is to a proper parabolic curve. If anyone has already done this, could you please let me know?

7. I think the easiest way to check would be to pin a string to a wall (or get two people to hold up the ends) and place the bow over top of it. I'm pretty sure you could get a near perfect curve with this method.

8. Originally Posted by Whiskeyjack
I think the easiest way to check would be to pin a string to a wall (or get two people to hold up the ends) and place the bow over top of it. I'm pretty sure you could get a near perfect curve with this method.
Yes, that will work! The only problem is not having a 10+ foot wide wall for me to use - I'll try it anyway with a shorter pipe section and post back.

Meanwhile I put an edge on one panel - *for anyone who feels that making a tarp is difficult - it's not! I put a 1/4 inch hem on the sides and bottom on one panel in less than 40 minutes! If you can sew a straight stitch, you'll be fine.

Here's pictures of me doing this. The short hallway is too short to show the entire tarp, but the cat cuts came out just fine.

9. I used a 5' pvc pipe section set to give a 3.5" depth and hung it on the wall along with a piece of string - note the string isn't flexible enough to give a even curve (it's braided masons line) - The string curve is very close to the pipe curve. I'm happy with this as it is.

10. Just find yourself an outside wall of a house, or maybe a walmart. Should be plenty long enough.

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