As I'm typing this, I'm currently grading Simplicity 5250. Can you believe that I'm nuts enough to actually grade the jacket here and not the pants? Me neither. But I am. I thought that it would be a good chance to practice grading. I needed just one size bigger. This is a 32 1/2 inch bust and I needed a 34 1/2 (or 35, but I went with 34 1/2 to make it easier) inch. So I thought I would do a post on grading. I've found this article on Threads to be most helpful and it goes into great detail about how to grade. I'm just filling you in on my experience.
Here I've done something that you probably shouldn't do but I did anyway. Alter the original pattern. If this had been an older pattern, predating the 70's and not a jacket with so many pieces I would have considered tracing the pattern and then using that to alter with. But I'm sticking to my guns on this one. I altered the original pattern, so there. You may not want to do this. That's up to you. And don't let anyone tell you different. It's your pattern.
Onto the grade. I started with the back lining piece as it most closely resembles one of the 5 main slopers on the chart from the Thread's article. I drew the lines in (accented here in red) and then figured the amount I needed to grade each line. The Thread's article will help you with that too. The graph in the article goes up to two inches, however, if you need to do a bigger grade, multiply the graph. I did a two inch grade here. But if I were to do a four inch grade, I would take the numbers given in the graph for a two inch grade and double them. Make sense?
To get a good and even grade, I drew the grading lines in the same places of origin. For example, the horizontal grade line in the middle of the armscye should match the grade line of the sleeve head and the front lining piece. You with me? Good. I did this part by laying the pattern pieces over each other, matching them all up. For example, as I graded my back lining piece, I also put the lines in for the yoke, the back pleated section, the belt, the peplum, the collar and the sleeve. All the pattern pieces must grade at the same points for the grade to work. In other words, you can't just pick random lines for grading, I've done that one before and its a real pain to figure out where you went wrong. Everything gets all wonky. Have the grade lines all originate from the same points.
Next I spliced and separated the pattern pieces one at a time. Added in the tissue and used my ruler to determine the amount of extra tissue I needed. If you are grading down, you obviously won't need the tissue. You'll be overlapping the pattern pieces instead. In the end, my piece looked graded, ha ha ha (A for effort, right?). Where needed, I neatened or blended the edges of the grading areas with my straight ruler or french curve. After that I went through all the pieces and matched them up again, laid them over each other, etc and made sure that the notches matched each other (otherwise, I remarked them) and that there wasn't a piece longer or shorter than each other. I find it easier to sew the garment if the notches and seams all match up. Who doesn't, right? Ha.
A few things to keep in mind. When grading a top or a dress, stick with your bust measurement. With bottoms, stick with your waist or hip measurement depending on which is bigger or harder to fit. Once you are finished grading a pattern, its a good idea to make a muslin, just to make sure that the grading worked and you don't have one piece longer or shorter than the other or something somewhere doesn't quite match up. That's up next, for me. Also, I wouldn't bother grading a pattern if you're only 1 to 1 1/2 inches off from the pattern. Instead I would make a muslin and fit from there. If you are 2 or more inches off, you'll need to grade.
Hopefully this makes sense. How do you normally grade a pattern? Any tips or tricks you've come by that helps?