Heat creasing silnylon prior to hemming (no pins or clips)

This technique can also be useful with polyester fabrics. Nylon will tend to shed creases as you noticed but polyester will retain them. Think of ironing a crease into polyester slacks. My only concern is the effect of the heat on the waterproofing.

I just completed  a rain kilt of silnyl, on which I  tried to use a rolled hem foot.  After a lot of struggling with the rolled hem foot, I decided to press the hems in with an iron and try to sew them.  Same results as you got, it was easy peasy.  Much better results than I was getting with the foot.

That’s pretty cool, thanks. I hate sewing with silnylon because it is just sooooooo damn slippery, I can’t keep anything in place.

Philip – I’ve had good luck with the standard basting tape from my local sewing shop. People say it won’t stick to sil, but I find that after i run my nail along the seam it sticks just fine. Sail makers commonly use basting tape, but it seems to be less usual with the people here. On its own or combined with this folding technique, you should be able to tame your silnylon issues.

Ken,
When doing lap felled seams, I always crease the fabric panel edges first so the edges of the pieces to be joined will overlap perfectly. It is a little tricky, because the crease lines have to be outside the seam lines drawn on the panel, such that when the seam is sewn, the line of stitching will be centered between the creases. But once you figure that out, you will have a true flat felled seam

It is much easier to make a faux felled seam, by just stitching at the seam lines of each piece to be joined, and then folding the seam allowances over on one side and adding one or two lines of stitching, which gives the seam the appearance of the true lap felled seam; however, it will not have the water resistance of a true lap felled seam, because the first line of stitches is not protected by 4 layers of fabric.

So if making true lap felled seams, the creasing simplifies laying up and overlapping the seam allowances before pinning and sewing. Some don’t like pinning because the pin holes reduce water resistance, but if the pins are fine, and set between where the stitch lines will go, the pin holes will be going through 4 layers of fabric, and will not expand to reduce water resistance as on the faux felled seam. But the faux seam is fine for heavier fabrics, as when sewing a pack.

For a thin fabric, as on a tent or tarp, in addition to the seam lines, the crease lines must be determined and marked, and the seam allowances trimmed to just the width necessary for the fabric edges to overlap just enough to produce the desired seam width. Looking at lap felled seams in a gear shop helps to see how they are configured.

Every fabric is different, so before creasing, creases are made with the iron on a scrap of the fabric, gradually heating up the iron until a good crease results without melting or damaging the fabric. The whole process sounds difficult, but actually makes the sewing faster once you get used to it, and you get a stronger and more waterproof seam.

I remove each pin just before the fabric goes under the presser foot, producing a tighter seam, and also sew some lap felled seams on scraps of the fabric beforehand to get the right thread and thread tension. I also hold the fabric both in front of and behind the presser foot during sewing, maintaining just the right tension to produce a good stitch line. These steps will reduce wrinkling of the fabric along the stitch line. Having steady hands like a surgeon also helps.

I’m sure it’s easier to use a device on the machine to make the felled seams more quickly, but that also takes time to develop skills using the device, and for just one tent, the above approach works fine.

Kudos to those who can bond, rather than pin the fabric, with or without stitching. Although I try to design tents with a minimum of seams, there are still enough of them to make bonding too much work and messy for me, particularly if each bond must be clamped along the whole line of the seam. Judy Gross of Lightheart gear is a master seamster, and once expressed how daunting and messy bonding Cuben tent fabrics was for her. That would go double for elastic fabrics like silnylon. So I decided not to go there.