this was a standard backpacking gear diy chapter in a standard backpacking book from the 70s. Nothing odd, and it's easy to see why it works to iron out the folds then hold them together then sew them, just doesn't work with silnylon, and nobody here would make a tent out of 70d nylon, times have changed, so it's not really relevant, the point was it's quite easy to iron a fold into two sides of thicker non silnylon nylon and have it hold the crease, then pull them together and sew a true flat felled seam. I remember the way it was written, it was obvious that's how you do it with that material, we just can't use that method now because silnylon won't let you, and sewing cuben is sadly frowned on, even though it holds folds perfectly. Keep in mind, the 70s had nothing like what you see today re geeking on this stuff, you really could learn most of the methods from one well written chapter or two, and it could be taught/written easily. Now is a different matter, for better and worse.
Wait, I see, you missed / misread, I said make your own gear, myog, that's the chapter I was discussing, you must have missed that. It was talking about making your own gear, way back then imagine! Of course we know that machines do the work commercially, that's not what I or the book was talking about, it was talking about how you can do it yourself. Clear? I am not, and the book was not, talking about how factories or shops do it. Same then as now, how to do it yourself, man I wish I'd paid more attention back then, grrr, but i always thought sewing was just impossible to learn.
I wonder if I still have that book somewhere, probably not.
But I'm not personally concerned, a faux seam is fine, it's just faux, and the perfectionist in me wonders about that faux thing, 4 layers are > 2 layers, that's just a fact. I'll take a look at my tents to see what they did, I know the asian sewed one is going to use the standard methods since they have expensive sewing shops with cheap labor, at least for the higher end gear, easy to see the difference on the complexity of the patterns they work with, number of seams, curved cuts, all that. My respect for asian seamstresses is far higher now than it was, even though I know a lot of the gear is done with automated machinery as well.
I won't be buying such a machine though, double stitching, and given tarptent was doing a fine job without one from what I can see, if it's good enough for them, I'm fine with it, they have good quality, good enough anyway. A hemming presser foot would be nice though, I think I'll get one of those and try it, worth the 15 or so dollars, I don't enjoy pinning the hems at all, boring.