How to create grade rules 2
For the previous entries in this series about the grading and sizing of clothes, see here, here, here and here. Reminder: for purposes of explanation in the exercise of deriving grade rules, we’re using the CS151-50 (open source). I’ve linked to it enough times in the previous entries so you should have it by now.
The first thing I did was to sort out the measures most likely to be needed for the average bodice and bottom. This spreadsheet can be found here in the forum. For this exercise, we’ll cover the girth portion of tops, leaving length grades for tomorrow. In the girth portion of the spread sheet (screenshot below), we have chest girth, waist girth, neck base girth, armscye circumference and upper arm girth.
Perhaps the screenshot looks a bit confusing; it’s set up to be used by a grader. The base size is 5 which means that the grading value for 5 is zero because you’re going up and down from there. The sizes to the right of 5 are indicated with a “+” sign. This means you’re adding these amounts to the base size of 5. The opposite is true of the smaller sizes to the left of 5. With me so far? For the purposes of clarity, the discussion will refer to examples of making the pattern larger. The text becomes too complicated if I have to constantly refer back and forth to smaller or larger.
To derive rules from these, you have to know how patterns are graded. Nearly always, we grade backs and fronts separately. Additionally, we only grade a half front/half back. What this means, is that you may have to divide the size increase by four. Take the chest girth for example, you’d divide this by four. This means you’d grade a 1″ increase by adding 1/4″ to the half front and another 1/4″ to the half back. Since you’re only doing half garments, doubling that to the full garment would mean you’ve got the full inch you need. You’d repeat this operation for the waist but afterwards, this can get a little tricky.
Consider the neck girth. Your total size increase in the neck is .375″. Do you divide this by four? And if so, how do you account for it? This is a little trickier than you might suppose. Logicking your way through it, you might think that you’d add up to the neckline at the shoulder juncture and call it good, but think a moment. The neck is a cylinder. If it’s getting bigger, it means it’s getting thicker, cutting into the existing shoulder line. In other words, grading that point means making the neckline wider at the shoulder line. Still, it will also need to be longer at that point, making the neckline deeper over the previous size. So, this means you need a bit of a fudge factor. Go ahead and add in another 1/8″ to make matters simple. Your total neck girth grade then becomes 1/2″ (including the previous 3/8). Divide that by four and you’ve got an 1/8″ per side to adjust for at the neck/shoulder juncture. Still, this isn’t the whole story. Due to the position of the neck, part of it (side to side) is actually a length measurement too. Cutting to the chase, you’d increase the neck width by 1/16th and raise the shoulder at the neckline by another 1/16th to get your full 1/8th per quarter segment. Are you starting to get an idea of why grade rules are highly proprietary? If they were easy, you could find them as easily as ants at a picnic.
Armscye girth is the measure around the arm at the base where it meets the body. In these charts, the girth increases by 1/2″ per size. However, due to its position, it’s a side to side and up and down grade like the neck but also divisible by four. It might help to think of the armhole as a box seen from the side view like so:
In strictest terms, the correct way to divide this isn’t really by four. No no, that’s just a starting point. Rather, half the 1/8th at the top of the armhole goes to the front shoulder and half the eighth goes to the back shoulder line -in other words, raising the shoulder line 1/16th both front and back. I’ll bet that’s as clear as mud.
On the other hand, the sides of the armhole “box”, the 1/8′s front/back sides of the armhole are not a cause of concern, at least the width of the armhole isn’t because this is accounted for when you grade the front and back for girth at the chest line. Make sense? However, you will need to grade the armhole longer, which is something you’d have to do anyway (under length rules). I just want to bring up that some measures can be tricky. They’re listed as “girth” but you have to put “girth” in the proper context.
Sleeves are probably the easiest; the girth part is. In this chart, the arm girth increases 1/4″. You’d put half that in the front sleeve and the other half (1/8″ actually) in the back sleeve. But don’t forget the sides of your armhole girth box (above). Your sleeve is growing an 1/8th in length from shoulder to armpit so you have to raise the sleeve cap the same amount as you grade.
So…do you think we’re done adding girth? We covered chest, waist (same as chest), neck and arm…is that all? Brownie points to everybody who said “no”. What about that shoulder line? Is this a girth measure or a length measure? Actually, it may be at this point that you realize girth and length are poor substitutes for horizontal vs vertical measures. Since girth is really horizontal measures, we need to add length to the shoulder line. So how do you calculate what’s needed for shoulder length if you have no measure in the CS151-50 to start from? That’s easier than you’d think. First, what’s your total chest girth -per segment? That’d be 1/4″. Halving that for the shoulder length is pretty close. In sum, you need to add 1/8 to lengthen the shoulder line.
Tomorrow I’ll show how these grows are translated (“mapped”) to the paper pattern. Second, I’ll show the increases for the length grows since we only covered girth grows in this segment. After that, I’ll show the mapping for both grows on the bodice.