Poka Yoke pattern making

Posted by Kathleen Fasanella on Oct 31, 2005 at 3:07 pm / Lean Manufacturing, Patterns, Sewing / Trackback

By now, all of my readers know I’m enamored of lean manufacturing and I try to apply it specifically to sewn products manufacturing. One of the things I wrote about extensively in The Entrepreneur’s Guide… was error-proofing your patterns; the lean concept to describe this is called Poka Yoke (pronounced “poh-kah yoh-kay”). An excellent introduction to Poka Yoke can be found here. By the way, check out this site’s management topics sidebar for very nicely written and presented information. Poka yoke comes from two Japanese words - “yokeru” which means “to avoid”, and “poka” which means “inadvertent errors.” So, poka yoke translates to “avoiding inadvertent errors”. This is the best site on the web for Poka Yoke. Please visit; the main page is a riot and thanks to Eric who sent me the link (each of the poka yoke pages are represented by a photo of a different pocket protector -who says geeks don’t have a sense of humor?). Poka Yoke is kind of fun to look for too, you already know lots of examples of it. For example, your coffee grinder. If the cap is not aligned properly, it won’t grind. Similarly, you can’t spill coffee while it’s being ground, saving you the potentiality of a lot of mess. As the mother of a smoothie-making child, I can only hope we’ll soon have a blender that works the same way. Another example of Poka Yoke is a ground plug; you can only get those in one way. Poka Yoke is a great concept because people rarely make errors when they’re focused and “on top of it”; people make mistakes when they’re distracted, tired, irritable, hungry or whatever. Anyway, today’s topic is Poka Yoke pattern making.

Above is a technical sketch of a leather jacket. I realize that the left and right side of the sketch don’t match. I drew it that way to show how it’d look if you sewed it with fringe and hair pipe and the other side without it, so ignore that; that’s not the point of this discussion. Notice the “V” in the sketch below

This “V” is what I want you to notice, it is perfectly matching at center front. Now, if you’ve never made or sewed a pattern like this you’re probably thinking this is no big deal. If you have made or sewn something like this, then you know that the center front pieces are not mirrored; these are not 2 pers. In other words, the upper right front is different from the upper left front. Likewise, the lower right front and lower left front are not the same either. To keep things simple, I’ll be using the lower fronts as a sample since the pieces are small. (see below).

Looking at the pieces in the photo above, you can see that these pieces look so similar as to cause a great deal of confusion and error even if you are paying attention. If you cut the 2 upper and the 2 lower pieces the same, the “V” will never match up. Anyway, there is a poka yoke to prevent the mis-cutting of these pieces.

The first way we prevent the mis-cutting of two nearly identical pieces is to use green backed pattern paper. It’s easy to flip pieces not realizing it if you’re cutting out a jacket like this because there are so many pieces to the coat and it’s easy to lose track. See the photo below for this example. If you accidentally flip your pattern piece, the green side can’t be missed so you quickly turn it to face manila side up. This poka yoke is similarly invaluable if the person cutting doesn’t speak or read English.

Below you can see a comparison; a photo of the left and right pieces laid on top of each other. Since I’ve laid them as “mates”, one side is green. This makes it very easy to prevent the mis-cutting of these pieces. You’ll notice the manila colored piece underneath is not the same shape as the piece above it.

Still, the green back pattern paper is not the only poka yoke in use here. As I mentioned extensively in the production pattern making section of The Entrepreneur’s Guide…, you need to off-set your notches to prevent the wrong pieces from being joined to each other. You should also examine the notches along the top edge in the photo above and you’ll notice the notch on the reversed (green) piece does not align with it’s “mate” underneath. These mis-matched notches are another poka yoke.

For example, in the above photo, I’ve laid the lower front right on top of the upper right front, right sides together in the position they would be if you were sewing it together and you can see that the notches on that sewing edge are perfectly aligned. But let’s say that somehow the pieces were mis-cut anyway -in spite of using the green back paper- and you tried to sew the wrong sides together, in the photo below, you can see the matches will not match up. In real life, your stitchers will stop sewing immediately and start looking for the right pieces because they’ve got the wrong ones in hand.

However, you should notice that each of the lower fronts have a notch off to either the left or right (depending on their position) and each of those notches are exactly aligned because once the upper and lower fronts are joined, they will be sewn to the side fronts. The side fronts are mirrored pieces.

Anyway, these are some pattern making poka yokes. These are the kinds of features that are incorporated into a production quality pattern and unfortunately, books don’t tell you anything about this. Failing to have these kinds of features is usually why there are sewing problems with DE products. Writing posts like this really makes me wish I could just drop everything and write a production pattern making book; it is so needed.

If you’d like an example of the proper labeling and piece ID of the pattern, you’ll find that below.
1. Please note I wrote in all block letters. I used black ink (this is a shell/self piece) and notice the direction of the writing.

2. Please do not -do not!- write on pattern pieces the way many teachers or pattern books tell you to do it (up and down along the grain line).

3. You’ll notice the directional indicator [R] is circled. The words “Face-up” and R.S.U. are a redundancy (Right Side Up). To prevent mistakes, being redundant is good.

4. You should mark the wrong side of the pattern with an “x” which always means “do not use”. Sometimes I also write W.S.U which means Wrong Side Up. Pieces are never cut wrong side up.

5. Lastly, as this is a leather pattern, I’ve marked the direction the nap should be when laying out this piece. You should only use arrows on a pattern piece if it has a nap, and then, only one. Do not use a set of arrows on either end of the grain line like they do in home sewing. You only use arrows to indicate nap and if you’re indicating nap, your one arrow will only point in one direction.

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