Pop Quiz: Designing a t-shirt sewing cell

juki_app1Here’s a different kind of challenge for you -beginning industrial engineering using the simple example of t-shirts. Are you excited yet? Don’t go away, it could be fun and you may be surprised at how well you do. But first I want to tell you about a free Juki app for iPhone and iPad (HT: Jessica Montoya) because it can be used as a sort of cheat sheet and also, I am using some of the images from it (without permission) but Juki may look the other way if I plug it. Then again they may not, they’re tightening down their IP. But anyway, the app is pretty neat.

The Item List screen loads a selection of products to choose from. You pick an item and the application loads a schematic of the product with its seams in call outs listed by number. Below the schematic, each number lists the kind of machine you need to form the seam along with the model numbers. The model numbers themselves are also hyperlinks so you can read about the machine, its specifications et cetera.

Now back to our challenge which comes in two parts.  You don’t need the application to do this challenge and can instead, follow the provided links above. For what it’s worth, I didn’t use the app to come up with what I think is an optimal solution.

Part one: examine the schematic of the product (the tee shirt) or use your noggin and figure out what kinds of machines you need. You can be very general, you don’t have to list machine model, just say “overlock”, “cover stitch”, “single needle” or whatever. I will tell you that for the purposes of this exercise, the tee is not made of tubular knit so there are side seams. Also, the shoulder seams are taped.

Part two: now figure out the ratio of machines needed. For example, let’s say someone is starting a tee shirt sewing factory with six stitchers and they plan to buy six machines. How many of each machine should they buy? Four overlocks, one coverstitch and one chainstitch (4:1:1)?  Or should they buy two of each (2:2:2)? Or none of the above? Why or why not?

If you haven’t figured it out by now, this is a real life example. The person starting the factory has made good choices about the needed machines but not with appropriate ratios. In my opinion that is. So being that he is a good sport, I’m posting this challenge to see how many people will come up with responses similar to my own (because of course I think I am right). I also want to read how people have rationalized their decisions (because I could be wrong).

If you needed a nudge to work the problem, consider how many of each seam type there is and how long it is likely to take. Keep this in mind to prevent bottlenecks while also realizing that some machines are much more costly than others. Meaning, a 2:2:2 ratio would certainly avoid bottlenecks (mostly) but some machines might be underutilized while incurring greater purchasing expense. For example, the cover stitch machine is roughly 4 times the cost of an overlock.

So good luck and I look forward to reading your comments. Oh, and we have a prize for a winner! Lisa Bloodgood has donated two books as a give away. The winner can pick which one they want. The two titles are Pattern making in Fashion and Pattern making in Practice (same author).

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  1. Jessica says:

    Glad more people are finding out about the Juki app!

    I think some of the machine needs depend on exactly how the collar is attached; if the collar is attached with a coverstitch, than I would want two of those machines so that one is set up up with a folder for hems and the other is free for any collar binding attachments. I wouldn’t want to be changing out attachments all the time, so would have machines set up for each type of operation. One double needle chainstitch could be set up to tape the shoulders (into the back neck?). The overlock will be used for more operations than any other machine, so I’m going to say 2 coverstitch : 3 overlocks : 1 double needle chainstitch.

    If bottlenecks are still an issue, maybe you hire 5 stitchers on 6 machines and have one be able to float to other machines if needed, like a lean cell.

  2. Sandy Peterson says:

    I came up with 7 steps not 3 according to the app, but I am not overly familiar with all the machines. So here is my guess: 2 overlock, 1 lock stitch or chain – not sure which one, 1 cover stitch.

    It would be great Kathleen if you could list all the steps in order so I could see if I was on the right track or not. Thanks, this was “fun”(?) and (I only say that because……………..well, at least I tried). Also, I already have the Pattern Making in Fashion book.

    Thanks for this post.

  3. Tara Niscak says:

    I’ll give it a go. It’s funny, I’ve had that app for ages more as a curiosity than anything. Good to see how it is a resource for my future machine puchase planning.

    Depending on how you put on the neckband…

    I would say 3 overlocks (A): 2 coverstitch (B) and 1: double needle (C)

    First overlock the shoulder seams (A-1), next coverstitch the neck band to the body (B-1) and then stitch the tape over the shoulder seams and back neck (C-1). Overlock sleeves (A-2) and side seams (A-3) and coverstitch the armholes and body hem (B-2).

    I thought at first you could use one less overlocker – do the sleeves and side seams at the same time, but I forgot about the tag inside on the side seam ( hence separate into two steps would be easier?).

    Or Meaghan could be right, I don’t know exactly what a chainstitch machine does.
    Great challenge either way. I look forward to everyone’s responses. Thanks.

  4. Katherine says:

    I’m not sure how the shoulders are taped, but this is what I came up with

    6 overlocked seams (2 shoulders, 2 sleeves attached, 2 side seam & sleeve)
    1 coverstitch with binder attachment (neckband)
    4 coverstitched seams (taping shoulders, hem, 2 sleeve hems)

    I haven’t taken into account that some seams take longer to sew than others, as I’m not sure about this.

    So the ratio I have is
    6:4:1 overlocker:coverstitch:coverstitch with binder attachment

  5. Quincunx says:

    I am. . .cheating and heading straightaway to this entry on industrial sewing machine instructions, which as I recall were for a T-shirt. Oo, they are, and added that tape in the neckline which I forgot. I like that neckline tape. Even some of my pile-’em-high sell-’em-cheap T-shirts have contrasting tape back there now, and look and wear all the better for it. Let’s keep it even if it doesn’t show up in the app.

    After further cheating in the form of inspecting my husband’s shirts, the ‘better’ T-shirts have tape shoulder-to-shoulder, and the pile-’em-high sell-’em-cheap ones have flashy tape sewn into the neckline, with distinct sewing over the ends of the tape that I can’t visualize how to do in one pass with the rest of the neckline*, and different, plainer stabilizing tape in the shoulder seams. The flashy tape could possibly be sewn at the same step as the neckline*, the stabilizing concurrent with the shoulder seams, and no extra step whatsoever for shoulder-to-shoulder–that matches with the Juki app sewing instructions. Now either I’m wrong and shoulder-back neck-shoulder is all one pass no matter what tape style you’re using, or the desired T-shirt is going to require a more complex process than the one in the free app. For now, I’m going with the blog entry instructions since they also specified taped shoulder seams, so I’ll assume it’s right about the other marks of high quality being desired.

    . . .waitaminute, I forgot about the detailed chart below the sewing instructions. Sheesh. Someone already solved this problem for 1 operator per machine. I can’t take credit for this!

    *Can you force a double needle machine’s lines of stitching to converge? Can you use just one needle at a time? This isn’t a material which holds needle holes from being sewn with an unthreaded needle, so I suppose the same effect could be made by unthreading one needle and sewing as normal, if that wouldn’t screw up the thread consumption.

  6. David S. says:

    Quin: most double needle machines have needles that move in sync with each other. There are machines were one of the needles can be disengaged; they get used to sew things where there’s a sharp corner. You see them on top stitching on jean back pockets, and upholstery, for instance.

  7. sfriedberg says:

    Quin, with a split needle bar you can use just one needle at a time on a double needle lockstitch machine. This is used to turn nice square corners on inner and outer lines of stitching. Most double needle machines don’t have a split needle bar, but it’s a very nice option.

    However, there’s no such thing for a coverstitch or overlock machine. Once it’s set up and threaded, you have to use all the needles you installed.

    You cannot force a double needle machine’s lines of stitching to converge. However, there are pattern sewing machines (often used for things like jeans back pockets) that can sew converging or diverging lines of stitching. They work differently from double needle machines.

  8. Sarah H. says:

    1 Straight stitch, 3 overlock, 2 coverstitch to do the work most efficiently and be the most flexible.
    I based this on a plain t-shirt, with possibly a vented side seam and sewn in labels. Also I counted on circling in the collar rother than sewing it on straight with one sho seam open.

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