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Cutting panels from Silnylon

Posted: Wed May 17, 2017 1:15 pm
by sean_iow
I've decided to make a cat-cut tarp as a warm up for a more ambitious project. I had some fabric left over from a previous rectangular tarp I made so thought I have a go at a tarp with a catenary cut ridge to practice sewing the curved seam. As I was cutting out the fabric I realised that due to the way I had to position the templates that on one piece the ripstop is aligned with the ridge and on the other the ripstop is on an angle. The ridge is marked with an R on the fabric. Is there a correct way to have the ripstop weave aligned with panels?

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Re: Cutting panels from Silnylon

Posted: Wed May 17, 2017 6:40 pm
by Mariner
No idea about this but this guy seems to:
https://backpackinglight.com/myog_tech_ ... ry_curves/

Re: Cutting panels from Silnylon

Posted: Wed May 24, 2017 9:54 am
by sean_iow
I have looked at the maths, thanks. It seems there's quite a science to it but a further search comes up with that some people seem to think that it's not that critical due to the stretch of the material?

I've finished mine.

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The finished curve on the ridge is much more pronounced than it was when cut so there is some stretch going on. I would reduce the curve on a future one to give a touch more room inside. The side on pic shows how much the ridge curves.

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I did manage to adjust the guys and get rid of the wrinkles. The front pole is 900mm and the rear pole is 600mm. It gives a very low profile compared to when I pitch my flat tarp as a lean-to. I did run the hose over it and after a good blasting I did get moisture on the inside of the seam so I might have to seal this. The ridge seam was the hardest bit and it's a flat felled seam, although I don't think it's a proper one as it's done in two operations and only one row of stitches go all the way through. It is also a bit baggy in places on the inside at the fold. Do all tarp manufactures use a flat felled seam or would a normal seam be ok along the ridge? maybe with a line of tape sewn along the ridge to reinforce it, but this might have a different stretch to the silnylon so create other problems?

With regard to sealing the seam, have I read that a home made sealer of silicon bathroom sealer diluted down to a brushable consistency with white spirit can be used? I've still got May's Bivi A Month to do so it will get a proper test this weekend :smile:

Re: Cutting panels from Silnylon

Posted: Wed May 24, 2017 10:05 am
by thenorthwind
With regard to sealing the seam, have I read that a home made sealer of silicon bathroom sealer diluted down to a brushable consistency with white spirit can be used?
I've used this method on some panniers I had to sew up. Seems to work pretty well. I don't use them much any more but the seam still seems strong and watertight and they were in daily use for quite a while.

Re: Cutting panels from Silnylon

Posted: Wed May 24, 2017 10:17 am
by sean_iow
I've give that a go then thanks. I didn't want to splash out on a commercial sealer as this tarp is mainly just a test using some left over fabric. I'll sleep under it this weekend and see how I get on and if it's ok I'll go to the effort of sealing it.

Re: Cutting panels from Silnylon

Posted: Sun Jul 30, 2017 11:22 am
by mtbmarkymark
My Lunar solo just started to leak on the fly. I had never seam sealed it
i used clear silicone sealant , thinned down 1:1 with white spirit, mixed really well with a little whisk
i applied it with a 1/2" paintbrush which i had cutdown to make it thinner with scissors
you dont need much, think 1/2" depth in an old mug