First I thought they just used a flat felled seam, but I inspected the seams of some of my tents and now I don't know anymore. On seams from tent manufacturers you can see 2 rows of stitching on both sides of the fabric. With a flat felled seam you can see 2 rows of stitching on one side of the fabric, but only one row on the other side.

It looks like the seams from my Marmot and Helsport tents are made like this:


A felled seam is slightly different:


What is the effective difference between these 2 seams? Do you have any tips that will make sewing either of these seams easier with silnylon? Most sewing guides suggest using an iron to press the seams flat. Is it even possible to do that with silnylon or would I ruin my fabric if I tried?

I usually do a third row of stitches to make it a little stronger. Because I am an amateur sewer and my machine probably isn't that good. Then you have sort of a combination of your two above.

I sometimes iron silnylon that got all crumpled. They make cooking utensils out of nylon and silicone. Nylon has a pretty high melting point.

When you do the second row of stitches, you have to pull apart the fabric and push the seam flat as it goes into the machine. If it's not taut, then all the tension will be on the 2nd row of stitches and the 1st row won't do as much. Again, a third row of stitches will make this all moot.

I've never tried ironing my flat felled seam - I'll have to try that - I bet that will make it better - but then you waste a bunch of time setting up the iron and stuff...

Both of those are felled seams.[1] Manufacturers usually use a folding attachment and a double needle machine to make seams like this. As a practical matter there's not difference in the performance of the two types. Manufacturers use the first, because it can be done in one operation, which saves a bunch of labor, at the expense of requiring a bit of equipment. If you care about the looks, you can top stitch through the seam. If you can stitch parallel to the original stitches, it will look just the same.

You can iron silnylon with a cool iron, work on scraps, to make sure you're not going to damage it. I've never felt the need.

[1] Technically, some standards, including ASTM D-6193, call the second one a 'Mock felled seam', because it's done in two operations, and it's actually two seams superimposed on each other.

Edit: It's important that the second seaming operation of a mock felled seam penetrate all four layers of cloth. It's not the end of the world if it misses a few spots, like if you've got tight curves, but it is an important part of the strength of the seam.

Also, if you read home sewing blogs or discussions, you may see mention of another sort of 'mock felled seam'. That's a plain seam that's pressed to one side, and top stitched down, so it looks like a felled seam. It's not a terribly effective seam for gear, and it doesn't do a good job of keeping thing sfrom unraveling.

Edited by dscheidt on 04/07/2012 21:01:50 MDT.

Thanks, that answers my question. Now the fun can continue without me worrying if I should do something different.

Edit: NM. Re-read your OP more closely. FWIW, I've found the "mock" flat felled plenty strong.

Edited by DavidDrake on 04/07/2012 11:33:52 MDT.

The thing about the third row of stitching is, that with the 2nd row, I keep stopping and folding over the next section - the tension isn't totally uniform...

If I do a third row, I just feed it through without stopping, so it's more uniform.

It doesn't take long to do a third row.

It would be much more of a pain to have a seam rip out during use and then fix it at home.

But, you're right, probably over-kill

Jerry,
In your experience (far more than I have) is it that very first row of stitching that "sets" the smoothness of a cat-curved seam? Or do the second and third rows help smooth things out as well?

I get exactly what you're saying about the third row being far easier, once everything's been folded and stitched down. As you say, not much extra time for the insurance.

What I do is draw a line on both pieces of fabric where the cat curve should be, then sew the two pieces together, with the row of stitches ideally going through the middle of the line on both pieces, which makes the cat curve.

Thanks to the stretchiness of silnylon, if you're off a little it doesn't make that much difference.

If you screw up there will be puckers, rather than taut panels, which is probably more cosmetic if it's only a little

Mark,

As David S. stated, your second diagram is sometime called a 'mock' felled seam. It is also called a 'faux' felled seam.

It is much easier for an amateur like myself to sew, because once you get the first stitch line right, with the canopy taut, all you have to do is trim the seam allowances to the right widths, fold one over the other, lay the fold flat against the work, and sew the second seam.

Problem is - the faux felled seam defeats the purpose of lap or flat felled seams; in that it does not have the stitches in both seams going through four layers of fabric. Once the canopy is stretched taut, the faux felled seam, unlike the lap felled seam, will present one line of needle holes that is not backed up by additional layers of fabric. The only thing keeping the water out is the sealant. With the true felled seam, the needle holes in both stitch lines go through four layers of fabric, instead of just one layer. This does not show so well on your diagram, as you are showing the material X-sections in a less than taut position.

If you are working from a pattern, the seam allowances on the fabric edges can be folded over and ironed - very carefully to avoid damage to the fabric - and then the two panel pieces can be engaged and pinned so that a true felled seam will result when the seam is sewn with two lines of stitching. I remove the pins just before the material goes under the presser foot, as this seems to allow tighter stitches.

As a side note, when sewing Cuben to other materials, I intend to first fold over and bond the seam allowance on the Cuben, so that the stitch holes in the Cuben will be less likely to expand, as in Ryan's infamous photo in a recent article and post. Then the folded and bonded Cuben edge will be sewn onto the folded edge of the other material, with the folded seam allowances facing each other. The result will be what looks like a true felled seam on the outside, but with the seam allowances inside separated, and not wrapped around each other. But the thread will still be passing through four layers of material in both stitch lines, so much of the advantage of a true felled seam will be retained. This should also work better if a third material, like door netting, is to be integrated into the seam.

Hate to say it, but IMO the faux or mock felled seam is of little value other than for looks. If you just did a french seam, two fabric edges sewn together, and sewed binding strips over the seam allowances as seen on many cheaper tents, you would probably have a seam tht is less pretty, but also less likely to leak after sealing than with a faux felled seam with its line of open stitch holes along each seam.

If you are going to tape the seams as manufacturers often do, it probably matters much less if a mock or faux felled seam is used. But that adds quite a bit more weight than carefully applied sealant, I think.

Edited by scfhome on 04/07/2012 20:39:28 MDT.

The purpose of a felled seam is that the raw edges of fabric, which are prone to unravel, are all enclosed in the seam, and can't unravel. That's true whether you've got an LSc seam (a true felled seam), done with a double needle machine (or your pretty fiddly manual method, which I've done, but with easier to sew materials than what gets used to make tents with), or an SSw seam (the mock felled seam, done in two operations.).

I also don't get your complaint about waterproofing. With an LSc seam, there are two (or more, three and four needle machines are used in heavier goods) rows of stitching that penetrate from the inside to the outside, and two parallel pairs of stitching that can leak or wick water inside. With an SSw seam, there's just one, the other set of threads aren't exposed to the outside. (Alternatively, they're not exposed to the inside, if you chosen to make the seams that way.)

I have an old, or had, backpacking book, that included how to make your own gear, I distinctly remember it showing the standard felled seam, which was created by ironing the crease into both sides. That was 70s era, which means 70d nylon I believe as lightest normal.

The problem with silnylon is that it won't easily hold that crease, even if ironed fairly hot, and it slips so much while sewing it's unlikely you would end up with a straight line. Leading to using the faux seam, which is required because of the material shortcomings, not because of any technical thing.

I've eyed those double needles in the sewing stores, but those require a machine that supports them, too much money for me.

You can always pin the stuff too, pinning is fine, it's just a hole, and you're going to seam seal it anyway, just use the smallest pins you can find. I haven't done a tent yet, so this question is interesting to me too, re how to get that true felled seam.

I don't believe the faux seam is the same as a single seam however as suggested above, the force hits both stitches, from each side, which is obvious from looking at the above pictures, but it's right that the first faux line of stitching is only going through 2 layers, not 4, which is not as strong.

You can get felling presser feet, but they are I think for the faux seams, and assume the first row has been stitched, I believe. I haven't tried mine yet on silnylon though, so I don't know if it actually will work with that slippery material. The idea being sew the first seam, then just let the foot create the felled remainder, fold in then sew. Pinning does fine though for those two steps, just takes a while.

I have never seen a commercial tent made with anything but true felled seams. I'm not sure what tarptent does, I thought they used the double stitchers, but when I was seam sealing my rainbow I saw a spot where they had slipped and the double seams lines weren't parallel, so clearly at that point tarptent was doing a very good job of manually stitching the two seams. Didn't notice if it was faux or true felled though.

Edited by hhope on 04/08/2012 10:45:36 MDT.

Harald,

A properly made 'faux felled seam', as you call it, and 'true felled seam' are both stonger than the material they're joining. The only reason to prefer one or the other is money. If you're doing the commercially, the additional cost of double needle machine[1] is worth it because it saves a substantial amount of labor on every seam it's used on, and after you've made enough, it's saving you money. If you're working at home, or are a cottage-scale producer, you'about:blankre not likely to recover the increased capital cost of a machine that you can't use for much else.

You may well have had a book that told you the way to make a seam was through some incredibly unnecessarily complicated method. All that tells you is that you had a book that said that. Perhaps it was written by someone who had no actual knowledge of how things are done industrially, who didn't know of the existence of folders, of double needle machines, and so looked at commercially produced gear and figured out how he could duplicate it at home.


[1] a double needle machine is something like this:
http://www.juki.co.jp/industrial_e/products_e/apparel_e/2needle_e/lh3528a.html
which as two entirely independent needles, thread paths, hooks, and bobbins. It's not a single needle with two points, like you see at the fabric store; the only thing they're useful for are decorative hemming. They don't form a proper seam in either line of stitching.

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.

Edited by hhope on 04/08/2012 18:16:03 MDT.

as samuel puts it so nicely in writing, the fake seam, when under tension, allows stretched out holes to elongate so much, you an f'n SEE thru it.
i know about this. regardless of it supposed "strength being stronger than the material", if you can view daytime thru your seams, they are going to leak. this may not be the end of the world, but it is untidy looking an a stuff sack or something under a lot of pull.
all my stuff bags are built like that. someday i'd like to find an easy to sew solution for making a really sweet seam that won't pull the holes under tension.
i do make a pass, then fold it back and lay in another run, but as samuel puts it, this only works for one side of the problem, the other side is still wide open.
any real solution would require a third pass, and limit the depth/length ratio of anything small i could make. it's not a problem with tens and tarps.
using the smallest possible needle tends to makes it less bad.

that's my op on this important detail of a subject.

Peter,
Glad someone else has seen all that daylight. It is more with silnylon, as the low denier nylon material with silcoat is extremely flexible, and the little needle stitch holes along the edge of the seam get bigger under tension.

As for ironing the silnylon, that's how this one was done with 30 D from Quest:



The iron has to be kept to the fold, and not allowed to slip over onto the single layer of fabric that will not be incoporated into the seam, as partial melting will greatly weaken the material and reduce the water resistance. If just one seam is done at a time, there is time to interlock the panels and pin the seam into place for sewing before the fold starts to vanish. As was noted, it was much easier to do, working from a cut up old fly to use as pattern pieces.

But if you are doing a cat cut seam, for example, and have marked the seam line on the material, you have as much as you would from a pattern piece, and can fold the seam allowances at the line and iron. Experiment with the iron heat level on scraps first.

Should have done a diagram, like Mark did, to show how the faux seam leaves a row of unprotected needle stitch holes in just one layer of fabric. Oh well, maybe next time.

> I don't enjoy pinning the hems at all, boring.
You may not enjoy it, but pinning the seams is the ONLY way imho of getting a reliable neat finish. Free-hand always stuffs up somewhere.

Cheers

"...as partial melting will greatly weaken the material and reduce the water resistance"

the melting temperature of both nylon and silicone is pretty high. Nylon 374–663 °F according to wikipedia. I don't think an iron will get hot enough.

I've put iron pretty hot and not noticed anything

Like you said, test on scraps first

"> I don't enjoy pinning the hems at all, boring.
You may not enjoy it, but pinning the seams is the ONLY way imho of getting a reliable neat finish."

If you use the "faux" or "mock" technique, after the first row of stitches, when you're doing the second row of stitches, as you're feeding the fabric through, pull the fabric apart so there is a little bit of tension on the first row of stitches and carefully flatten out the folds of the felled seam you can get the two rows of stitches to equally carry the load.

Maybe not perfect, but pretty good, and the finished result will be strong enough so it doesn't rip out.

I think like already said, the true felled seam with double needles is more for labor reduction.

Pinning (or hand stitches) are good for aligning the top and bottom when you do the first row of stitches. Otherwise the top fabric will stick on the pressure foot and slide relative to the bottom fabric so by the end of the seam the top and bottom fabric are no longer aligned along their length.

Just my opinion : )

"Free hand always stuffs up somewhere" - I love the British and Australian slang, especially the profanity : )

Hi Jerry

I found that trying to gently pull the seam open, and keep the stitching straight, and keeping the seam folded down neatly, was hard; when the seam was curved it was VERY hard. The fabric usually ended up skewing. So I pin.

> I love the British and Australian slang, especially the profanity
I don't think it is regarded as profanity in Oz.

Cheers