question for sewing geeks

[schmalts]

I am working on my first rain fly/tarp with that material I got from wally world. This is also my first sewing project EVER. I have a few questions for you guys.
I am going to use grossgrain webbing to make line loops on the corners. With the stuff folded double over what size needle would you use in a machine??
Second, I am looking at the black cat style tarp instructions in a different topic and see that some guys trim the edges with grossgrain as well. When doing this are you laying it on top of the pre- hemmed rip-stop, or are you folding it in half and wrapping it around both sides. (what I mean is will you see it on both sides or only one?)
Third question, if you do not trim the edges with grossgrain how are you doing your edges? are you doing a single fold and hemming it where the cut edge can be seen on one side or are you folding it twice so the cut edge is not seen? If folding twice is it for a reason or just looks?

I have both halves spliced together and made the cat cuts to the body today. Need to get stronger material for the corner reinforcements and grossgrain tomorrow.
I did my cat cuts a lot different method than most I guess. I just laid a long piece of cardboard on the driveway and figured out that with a X wide piece of cardboard I needed a 7 inch drop on the ends of the cardboard edge when I swung a radius. I then had the wife hold an end of a string and kept swinging an arc with the other end starting at the center line and had her go further out until the arc swung past the lines I had marked as 7" down from the corner edges of the cardboard. I used the felt cracks in the driveway to keep everything squared up. Then held a marker on the end of the string and swung my radius, cut out the arc, then laid it on my rectangle tarp and adjusted the cardboard until it was anywhere across the marks I had on the tarp to be my desired corners. After all, it is a radius, so it really did not matter as long as the edge of the cardboard crossed the corner marks on my tarp.

[schmalts]

One more question. The instructons say this...
"Now to attach the webbing to the tarp. Without rings, wrap your webbing around the corner and line both edges up on your 2" mark. Using a light source underneath will help with this. When you're sure the ends and edges of the webbing are aligned, sew a double box stitch through both layers of webbing and through the tarp sandwiched in between. Tie off and heat seal your thread ends"

I looked on the net and for the life of me have no clue what he means by a double box stitch. Is there another name for this?

[te-wa]

its just 2 box stitches, I use about a 3 or 3.5mm zigzag and then another one 1cm apart from the first. Yes, the growgrain is folded over the edge of the sil. if you try a rolled hem on a catenary curve, the fabric will buckle and crease and cause all sorts of cursing.
the needle size depends on the thread. I have good work with a 80/11 needle and gutterman thread

[tight-wad]

I am going to use grossgrain webbing to make line loops on the corners. With the stuff folded double over what size needle would you use in a machine??

I use the same size needle with everything. Whatever came in the machine. I did buy a new pack of needles. Told the lady at Hancock's that I was sewing ripstop nylon and she said use this. Don't ask me what number...

Second, I am looking at the black cat style tarp instructions in a different topic and see that some guys trim the edges with grossgrain as well. When doing this are you laying it on top of the pre- hemmed rip-stop, or are you folding it in half and wrapping it around both sides. (what I mean is will you see it on both sides or only one?)

I haven't used grosgrain to trim the edges of my tarps, but if I did, I would fold it over the hemmed rip-stop so that you see the grosgrain from both sides.

Third question, if you do not trim the edges with grossgrain how are you doing your edges? are you doing a single fold and hemming it where the cut edge can be seen on one side or are you folding it twice so the cut edge is not seen? If folding twice is it for a reason or just looks?

Fold it twice; for functionality and looks. Function, get all those potentially loose threads tucked up tight, and give yourself a little stronger edge (3 layers of fabric vs 2). Looks, so you don't have to look at your less than perfect burn job on the edges.

I did my cat cuts a lot different method than most .... After all, it is a radius, ....

Cat's aren't circle radii, they are parabolic radii. They are different, Grizz can give you the technicals. However.... I've found that - when dealing with curves - the processes of 1) cutting, and 2) double fold hemming, and 3) putting reinforcement patches on the corners, introduce GIGIANTIC margins of error, so even with the best drawn template, your final cat won't be a "catenary". But starting with the right template will get your final product closer to right than starting with the wrong one.

[tight-wad]

I looked on the net and for the life of me have no clue what he means by a double box stitch. Is there another name for this?

Mike just said one box stitch offset from the other, which is what I do on a side or corner tie out. (I only do the zigzag on the "horizontals", straight stitch for verticals and crosses.) For ridge line tie outs I make two boxes in line on a longer piece of webbing.

[Brian]

For the grosgrain, I recommend first going around the tarp with a simple hem - this keeps the GGR from ripping out when the tarp snaps in the wind (I learned this the hard way). Then, fold the GGR in half like a taco and insert the fabric bit by bit, working your way around the tarp. Try and make it so there are no exposed edges of the GGR - it has a tendency to fray.

A number 80 or 90 size needle would work great. You can get combo packs at Walmart that come with a 70, two 80s and two 90's. Use the 80 for the ridgeline work, and the slightly larger size 90 for any trip work or thicker sections you are working with.

Brian
OES

[slowhike]

I looked again at the thread were you were trying to decide what the fabric was & in your last post, I saw were you were talking about waterproofing the DWR ripstop yourself.
http://www.hammockforums.net/forum/s...?t=5214&page=3
Have you already waterproofed it or are you going to do that after you make the tarp?
Let us know how that preforms over time. Also how much the finished tarp weighs.