Grading stretch knit patterns

Returning to the list of topics from the reader’s poll, stretch knit pattern grading is next so that’s what we’ll do today. To refresh your memory, I’d said, knit pattern grading the way that  Stuart does it which is very different from how we do it in North America. To discuss the dichotomy of Stuart’s approach requires that you already understand grading to see why his method is a departure from what we typically do and we can discuss why it may be better and easier. My role is best described as a facilitator of this discussion because my experience with his method is very limited, albeit successful. And by the way, I refer to Stuart Anderson whose website is better known as Pattern School. Pattern School is offline for now but you can easily access it via the WayBack Machine and all links I’ll use will direct there. Ready? Okey dokey.

Stuart says there are two types of grading, incremental and proportional. Traditionally, we use incremental which means we attach a value to grow or shrink a given point according to X or Y coordinates. [At right is an illustration of rules applied to a pattern the traditional way.]  Stuart uses another way, namely proportional. This requires calculating the degree of stretch in the fabric and using a feature common to CAD programs, stretch the pattern pieces in accordance with the stretch properties. Doing it this way can be easier, faster and more accurate than grading via XY coordinates.

For a simple example, let’s say the fabric stretches by 6% width wise and 3% lengthwise (this is actually less than the full extension, knit recovery must be included in the calculation of stretch). Let us say you also know that you want the pattern to change a total of 2″ per size (XS-XL). So you would do the math to figure out how that 2″ translates with respect to the stretch percentage. The formula can be found on Stuart’s page that I already linked to twice. It is better to do it this way because the patterns aren’t getting bigger than they should be once you consider the stretch. And I know, we traditionalists guesstimate that a 2″ grade actually means we should use 3/4″ or 7/8″ instead of a full inch per back and front but that’s what it is -a guesstimate. Using this proportional method means no guessing! The added benefit is that newer graders can catch up more quickly with experienced graders who have developed (over many years experience) arcane rules of thumb.

The solution is to use the stretch/shrink tool in your CAD system to grow or shrink each given piece by the percentage you’ve established. This is pretty simple for a tee shirt -but what if you had a very complex style with side panels, yokes, pieced sleeves and all that? If you grade the traditional way, you have to spend some time figuring out how much of the grade goes here or there so the garment is proportional to the mid range size. With Stuart’s proportional method, you can forget doing any and all of that (we’re free! we’re free!). All you need to do is apply the same exact percentage to every piece in the pattern. Too bad this won’t work for wovens…

Of course, I have to try these things out. It is not so much that I don’t trust Stuart but I have to do it to understand it. My concern was that seams might not measure –exactly– to line up again with the pieces they sew to —but they did.

After I graded several pattern proportionately, I mapped the pieces by stacking them and “graded” the piece as we would traditionally to see what the grade rules were of the proportionately graded pieces. I have a screen cap below but there is also an excel file if you want to look at it more closely. The conclusion? These grade rules don’t look anything like what we typically see. Very complex stuff, too complex to actually attempt to do it traditionally.

stretch_test_graderul_chart

See what I mean? Those are some hairy grade rules. Traditionally, every point (1-6) would be the same for all sizes or if not, there would be a readily identifiable pattern.

Questions? Comments?

I have some pending issues with this as it relates to my CAD program knowing I have a graded set -which I can post about another time. I also have a help ticket (in a manner of speaking) out with Stuart so following up is not a problem. I wouldn’t be surprised if Stuart drops in to impart some of his imitable wisdom.

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