A while back I got an email question about shirt seams from a reader looking at the chain-stitched seams on his shirts and trying to make sense of them. Here's my reply, fwiw:
"What you're seeing on your shirts is not, strictly speaking, a flat-felled seam. It's an industrial technique that requires a chain-stitch machine with a built-in folder that wraps the two seams around each other and stitches them down twice (or three times) all at once with a double (or triple) needle, as opposed to flat felling which is done on a standard lock-stitch machine (like all home sewing machines), and requires two passes under the needle, one to close the seam and the second to "fell" it, as described in my book that you have. (Lockstitch machines can use double or triple needles, too, but they don't chain stitch, so all the threads from the multiple needles are caught by a single bobbin thread, resulting in a zig-zag on the wrong side.)
Here's a pre-production screen shot from my new book on shirtmaking, coming out in June 2015, which shows the construction difference :
And here are some shots of the finished difference on shirts I own (a Paul Stuart, and a Charvet):
...and shirts I've made:
Hopefully you can see that these all have a very narrow (1/8-in.) side seam with a single row of stitches on the outside and two on the inside. When I wrote my book back in the 1980s, this was typical for expensive dress shirts, like Brooks Bros, and the two above, which is why I chose to describe how to do it in my book, which is all about high-quality dress shirts (the new one's about all kinds of shirts). These days it's much rarer to see this, as you've noted, even on expensive shirts, simply because it's slower to do, and factories all have the fancy machines.
And these days, the chain-stitched seams have even become something to show off, what with the current interest in work-wear, and in classic American factory craftsmanship, so you'll see lots of expensive designer work-shirts with their chain-stitched thread ends untrimmed and dangling off to make sure you notice that they're done this way. You can see many examples of this on my Pinterest board about side-seam gussets, a related technique usually reserved for work-shirts, here:
Some home sergers these days can do chain stitching (one needle at a time), so if you want to simulate the effect on your shirts, you can sort of do it, but the double pre-folding will be tricky, and you'll still need to make two or more passes under the machine.
You can read more about the whole question of what's "better" here:
...and make up your own mind with the links here:
...and read about (and watch) the specialized folding/chain-stitching machines from the links here:
Check those out and you'll know as much about shirt side seams as I do:)"
I recently saw a video on flat-felling from Janet Prey, who's aunt Margaret Islander had apparently been a contract sewer for Nudie of Hollywood in the 50s, (creator of MANY astounding cowboy shirts for Roy Rogers and the like), and she claimed that Nudie had taught his sewers to make FF seams exactly as shown in my top diagram, in two passes but without a specialized foot, and with the folded width ¼-in. instead of ⅛ as I'm showing here. Seems obvious to me, having used the foot which works this way (and has been available to home and factory sewers since the later 1800s to judge from old sewing machine manuals I've seen), but she claimed that it was "revolutionary" at the time, or something like that.
I'm very eager to see everybody's further pix and thoughts!
Edited by dpcoffin, 30 April 2015 - 03:39 AM.