Flatlocking compared to cover stitching and overlocking

While everyone’s away at Market -some designers say the technical stuff I write makes their eyes glaze over but then that’s how I feel when they start talking about marketing or fashion in general so that makes us even- we’re going to talk more about our favorite subjects, sewing and patterns. Yeah! Today specifically, the topic is flat lock machines. Flatlock, without a space is also correct, you get different results with both in internet searches. If you don’t know, we all covet flatlock machines, yes we do. Everybody wants one -whether they need one or not, not mentioning any names. From the forum:

Can someone tell me what the difference between flat-lock/flatseam construction and a serge seam with coverstitch? I am going for the type of seam you would find on technical base layers (brand names redacted).

I’m not familiar with these brands but my performance running tights have flatlock seams. As to the difference:

A coverstitch is basically 2 or 3 needle bobbin-less top stitching that provides some elasticity. It doesn’t have to be used on an overlocked (serged) seam but usually is. The back side of the seam forms a ladder pattern or similar configuration joining the lines of stitching to and fro. This is similar to the effect you’d get on a home sewing machine with a double needle. The latter differs from a true double needle because these have two bobbins so their lines of stitching are not joined on the back side from side to side. Below is a drawing of a coverstitch seam on the left with photos of an overlock on the right (courtesy). There are various models, this one attaches ribbing and coverstitches in one pass. For this reason we also covet coverstitch machines, perhaps more than flatlocks.

A flatlock is different in several respects. Unlike an overlock, there are no layers to the underside, the seam is butted together (usually, exceptions). On a flatlock, there is no seam allowance with layers folding to the underside. Think of it this way, in the application you’re describing there is no seam allowance per se because the cut edges of fabric are butted against each other and joined flat in a single layer with thread. The flatlock stitching on the top and bottom joins the two butted pieces. Below is a photo of a flatlock seam (courtesy).

My contractor does not have a Flat-lock machine, but can’t you get the same effect by doing a serge seam and then go over the top with a 5 thread coverstitch? I have technical base layer wear and I have my own samples with serge/coverstitch and I am not seeing much of a difference.

The seam of the overlock/coverstitch as compared to flatlock is thicker because it has layers of fabric. First you serge a seam meaning there’s two layers of fabric the width of seam allowance on the underside. Then that is top stitched down with the cover stitch or if you’re attaching binding it’s done in one pass but there’s still extra layers there from the allowances. There’s a lot of thread concealing this on the underside which kinds of cushions and flattens it. However, the flatlock while also with lots of threads, has no seam allowance layers turned to the underside because the cut edges are butted against each other.

I want to get into some technical stuff, but I hear that a flat-lock machine goes for more than 30k.

Flat locks are definitely pricier than the average machine but I’ve heard price quotes closer to $3K-$4K, a tenth that price. Just this morning, JC showed me a site selling used Union Specials for $1,850. They also have a few Wilson & Gibbs flatlocks going for $500 but I think the price tells you all you need to know. If something sounds too good to be true, it usually is.

What would be the drawbacks of just going with serge/coverstitch or is that the same darn thing as flat-lock seams?

Flatlocking is used primarily for performance goods, it has fewer layers to chafe. It depends on what you want to do. If you’re running a marathon, you definitely want tights with a flatlock. An overlocked coverstitched seam, while it won’t pull apart, will chafe along your legs and cause bleeding. There’s other uses too; if you’re making apparel for children with sensory challenges, a flatlock seam is more comfortable. An overlock may or may not bother children (or even adults) depending on thread type but in active wear, you’d only use overlocking on seams of garments intended for light training.

It should be easier to find these machines than it is. These are also called “off the arm” or sometimes even “flat bed” or “flat arm” machines. Manufacturers are Union Special, Yamato, Kansai, Juki, Pegasus, Wilson & Gibbs and I’m sure others. Another way to shop is by knowing the seam class. I’ve updated the Seam class specifications entry to include a nifty six page chart that lists seams by the most common vernacular. The particular type you’re looking for is a FSa-1 seam.

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  1. April Femrite says:

    Very informative post Kathleen – now that I see pictures, hear the explanations, and go back and look at various samples, I can see and feel the difference.

  2. Leslie Hanes says:

    Man! I keep learning things I should have known long ago. I have a coverstitch, and have never attached ribbing with it. I have a binder attached to it, and it use it with and without the binder, but I have no idea how to attach ribbing. Most of my garments dont have ribbing, but maybe I would venture into doing ribbed outerwear if I had a better idea of what my machines are capable of doing. Perhaps many small manufacturers know what the machines can do before purchasing…not me. I knew enough to be dangerous, but when I saw an auction with a half dozen machines..I bought the lot. Now I’m still learning about them, 5 years later.
    Thankfully, the products we make seem to be doing fine despite my ignorance on how to improve. Thanks again, again,again, Kathleen, for providing the education even old dogs can benefit from.

  3. Robyn Ramirez says:

    I was wondering about that I have been looking at seam and seam finish chart and the cover stitch machine was confusing me. Thanks Kathleen!

  4. mirela says:

    My Singer Quantumlock serger can do a flatlock stitch and I’m sure it can be obtained to playing
    with the thread tensions in other sergers as well.

    See the stitches here: http://www.singerco.com/resources/serger_stitch_wkbk.html
    Flatlock stitch:

    The difference is that it creates a series of parallel stitches on one side and a non fraying stitch on the other side. By sewing twice over the same stitch I believe the same effect could be achieved.

  5. Seth Meyerink-Griffin says:

    I have a 3-needle, 5-thread coverstitcher that’s intended for use in attaching collars (long story short, I ordered online and flubbed up; the way it’s set up makes it difficult to use for general hemming and seam finishing). I’m going to check with my local industrial sewing supply company and see if there is a way to convert it (different foot, feed dogs, and maybe an attachment?) to general flatseaming without trimmers.

  6. harrabi hosni says:

    some of our customers (tommy hilfiger,CK,polo ralph lauren…..)request to macke this stitch instead of feld seam in the center front at crotch for all laidies jeans pants :
    1-if fabric is stretch: in order to improove workmanship in this area and reduce puckering
    2-if fabric is hard : in order to reduce thikness in this zone such as many layer may unlock this part and became hard also when measeurement of front rise are minus.
    still one thinks is that this kind of stitch cannot resist hardly in wash step and it may get off after wash and the feld seam still more secure comparing to it.

  7. M says:

    Great post! Thank you. I have been struggling to find a flat lock machine anywhere in Australia! If anyone knows where I can find one (even to import into Australia) I’d love to hear from you.

  8. Hera says:

    M > flatlock machines are usually called flatseamers in Australia. Look up Capron Carter, they had about 5-6 in their catalogue last time I looked.

  9. Audrey says:

    Reader from Amsterdam here, who is interested in acquiring industrial machines for starting a small webshop and sewing sportswear (yoga stuff).

    If a machine can do a top and bottom coverstitch, is that the equivalent of a flatlock?

    I’m looking at a used older industrial model 5 thread 2 needle Juki MF-880 which I believe does a top and bottom coverstitch: http://www.johnharbsew.com/images/threading/JUKI-MF-860-TD.jpg

    However, the online seller, who does not speak very good dutch, says that he has only been using 3 threads on the machine and according to the posted picture, it looks like he’s been making regular coverstitches. So it sounds like this machine is capable of doing both coverstitchs and flatseams? I think so, but I’m not sure.

  10. sfriedberg says:

    Audrey, coverstitch joins two layers of fabric on top of one another, while flatlock joins two adjacent pieces of fabric (at the same level) in a butt joint. Production flatlockers often have special trimming knives that cut away a small portion of each piece of fabric as the seam is sewn to ensure a perfect butt joint. This is similar to the knife action on an overlock (server), but takes place in the middle of the joint rather than the right side.

    Also, many (not all) flatlockers use four needles, while coverstitchers are limited to two or three. So the actual stitching is different.

    So, you might approximate a flatlock seam with a coverstitch machine, but it’s not really the same.

    This sequence of 8 webpages (http://www.the-needles-eye.com/TechInfo/36200/36200LapButtSeam/36200seams.htm) has some really good info on the various processes a production flatlocker can do.

  11. Audrey says:

    Thank you very much sfriedberg. I see…a butt joint like in woodworking.
    I decided to buy this Juki MF-880 in the meantime and the approximation of the flatlock seam will have to do for me (at least for now).

  12. Manan says:

    Just for everyone’s information:
    Difference between flat lock and flat seamer

    A flat seamer is a 4 needle with top and bottom coverstitch (6 threads). Machines are readily available such as Yamato FD62 series. You can find used in the US for $1800-4000. Very popular with stretch lycra performance wear. Although flat seaming is slower than overlock, it saves one complete operation if you plan on coverstitching.

    A flat lock is a 4 needle chain stitch machine with a top cover (9 threads). Quite hard to find and even harder to work on. The mechanics for these are long gone. Wilcox & Gibbs made most of these and some are near 100 years old. You can find some of the later green painted W&G machines for little money. Don’t waste your time. You’ll never get the four loopers timed. Uses shims instead of adjustment mechanisms. I scrapped close to 75 of these about 10 years ago (very heavy good steel brought great scrap price).

  13. Suzanne says:

    We have been using a serger to do 3 needle faux ‘flat locking’ as Mirela mentioned above with the ladders on one side and loops on the other. I see a couple people’s comments above that they have done this too. But I want to make sure we’re providing high quality and I’m curious if it is a weaker seam than the true flat lock or just slightly bulkier?

    • kathleen says:

      I don’t know because the best way to know, is to examine a sample and I don’t have this machine to try it out. Maybe somebody will post the info?

  14. jenny says:

    I see the faux flotsam stitch on so many garments, mostly in Discount; Budget or Mass Marketcategory garments. But i rarely see it use in higher brand names market categories such as Contemporary; Better; Bridge , Designer etc.
    Is there a reason the less expensive categories use this stitch and why the higher quality categories rarely use it, instead they choose flatseam or DNCS

  15. Lisa Hasted says:

    I have a Juki 634D since 1988. When I bought this machine I was shown a way to make a flat lock if needed. I use 3 thread, 1 needle. Serge your seems together and then pull the seams until the two layers become one like a flat lock. Wouldn’t this be the same principle as a flat lock machine?

  16. Mona says:

    This was an interesting article, but you’re not a marathon runner, right? I’ve run marathons in leggings that were entirely made on a domestic sewing machine, or with a combination of sewing machine and serger. No chafing and most definitely no bleeding. Of course for any production sewing a professional-looking finish makes sense, but it is more because people treat their clothes harshly or wear too small items.

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