Pop Quiz: Designing a t-shirt sewing cell pt.2

tshirt_seam_countFollowing up to last week’s entry, the questions you were invited to answer are:

  1. What kinds of machines are needed to sew tee shirts?
  2. What is the ratio of needed machines?

…all while keeping the constraint of only six machines total are to be purchased. What you were not privy to was that the customer had decided to buy 4 overlocks, 1 coverstitch and 1 double needle chainstitch which is why I wanted to do this exercise because I didn’t agree with the ratio.

Perhaps the first step is to itemize the sewing steps of the shirt. You can refer to the image off to the right for this discussion. There I’ve listed the seams for this product which isn’t exactly the same as the one in the Juki app.

Jessica was first to mention seam selection as being pivotal, specifically with the joining of the ribbing to the neckline. She mentioned coverstitching -which I also had but the customer said they were going to overlock the seam rather than cover stitch it. Jessica (and Tara) guessed a ratio of 2 coverstitch : 3 overlocks : 1 double needle chainstitch would be needed. Their estimate comes closest to what I had in mind.

The thing that bears mentioning at this point is the degree of difficulty and the time needed to execute each seam. While they must all be done properly, it is the coverstitching that requires a bit more finesse with folding, lining up the edges and making the seam lines match. Each overlock seam, while more numerous, would take relatively less time per seam. Therefore it was my opinion that only having one coverstitch (as the customer wanted) would create a bottleneck especially as compared to the greater output that would be created by having four overlock machines. The customer wasn’t willing to budge on adding another coverstitch (one costs about the same as 3 overlocks) so my suggestion was to only buy 3 overlocks rather than 4 and put the savings into something else that would surely be needed.

Continuing with comments, Tara analyzed the problem in the same fashion Jessica did. Sarah’s result was somewhat similar the difference being the question of construction which wasn’t clearly defined.

Quin’s comment was interesting with respect to the taping and double needling in that it reminded me that the customer may not have been aware how this is typically done. As I recall, the customer described taping the shoulder seams as two separate steps but ideally, this is one operation. If you survey shirts in your wardrobe, most shirts with taped seams have the tape beginning at one shoulder, curving around the back neck and then onto the other shoulder seam in one pass. While this might cost tenths of a penny more in extra tape, it takes less time in sewing if only due to the reduction of time in handling and aligning the separate work pieces. If it is done separately (excluding the back neck), the taping of the shoulder seams would be done before the ribbing is joined to the neckline. Additionally, I think sewing the tape to the shoulders and back neckline make for a sturdier product.

The only item remaining on the agenda is who wins the prize (the book Lisa Bloodgood donated); we have Jessica and Tara as the leading contenders. Jessica was first to respond but Tara was more precise in that she listed the needed seams and sewing order. I’m not sure I want to call this one. Should Tara and Jessica flip a virtual coin?

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5 comments

  1. Tara Niscak says:

    Yeaye! I’m just so pleased that I was even close to being right in my thinking that I will concede the prize to Jessica. After all, the early bird should get the worm.
    Thanks for the challenge Kathleen, that was fun!

  2. Prasanta says:

    I missed last week’s entry. So participating now.
    Where is the single needle (Lock stitch) machine? To make neck rib (joining two ends) and attaching main label with size mark (an optional if printed label is used)normally we use lock stitch m/c. Even back neck tape is attached by lock stitch.

  3. Jessica says:

    Agreed that it was a fun challenge that really got me thinking! Like Tara, I’m not feeling greedy about claiming the prize either, but a new book for my library is always welcomed.

  4. Quincunx says:

    . . .It did not occur to me to substitute a lockstitch machine for a double-needle chainstitch. Thank you, Prasanta. Every question I had about flashy back neck tape and different, plainer stabilizing tape is now answered.

  5. Andrew Schonbek says:

    OK – here I am, the aforementioned customer in the t-shirt sewing cell pop quiz.

    Thanks everyone for your thoughts on this. I have a manufacturing background but in a completely unrelated industry to garments, so this has been a great learning experience for me. I’ve been involved in the acquisition of some really complex production equipment in the past (3 D and flatbed laser cutting tools, 5 axis machining centers, turret punch presses, etc.) but none of this prepared me for the complexity of sewing machines in all their iterations.

    In the end, we did wind up with 4 overlock machines, not 3 (Kathleen won’t be happy about this). We had been negotiating with the Juki distributor in Romania (the project is located in nearby Moldova) but had not yet issued a formal purchase order at the time of my conversation with Kathleen that led to the pop quiz. Unbeknownst to me, the distributor went ahead and took the risk of ordering the machines to have them available for expedited shipping. Since we’re going to depend on Juki Romania for training, support, and other service we didn’t want to get off on the wrong foot leaving them stuck with an extra overlock.

    So now we’re stuck with it. I hope that our business will be successful and will grow and we’ll add a second cell. When that happens we’ll absorb the extra machine.

    In the meantime, having it will allow experimentation and time studies that will be getting underway shortly. This will allow real world confirmation of the optimum ratio, extent of bottlenecks, etc. When we have this data I’ll report back…

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