I give it a B-.
I kid, of course. I am just starting the process of grading out a commercial pattern to my size. I've selected a histrorical pattern from one of the major pattern companies but must increase it in size by a good amount as I am a rather stout girl. The pattern is Simplicty 9769 from the Fashion Historian series; in hindsight, I kind of wish I had selected Simplicity 2890 as it is a gored corset, and is available up to a size 24. I'd still need to grade it, but not nearly so much.
For those of you who aren't experts.... grading a store bought pattern is kind of a pain in the bustle. The steps:
1. Determine how many inches you need to add by comparing your measurements to the body measurements on the pattern. Usually they give just a few measurements - bust, waist, hip, back length. Divide the difference in each measurement in half, as most patterns are bilateral (if you are using a pattern that is not the same on the left and right side, ignore this).
My measurements compared to the pattern's for its largest size:
Bust: 52" measured - 42" on pattern = 10" total increase needed, halved = 5"
Waist : 47" measured - 34" on pattern = 13" total increase needed, halved = 6.5"
Hip: 51" measured - 44" on pattern = 7" total increase needed, halved = 3.5"
2. Determine how many seams are available to increase. On this pattern, there are four seams that can be let out (and if needed a little can also be added to the center front and center back). Each side of the seam will be increased, so I will be adding 1/8 of the necessary amount to each seam. For me, this means I will be adding 5/8" at the bust, 7/8" at the waist, and a little less than 1/2" at the hip on every edge except the center front and center back.
3. Make a copy of the pattern pieces as they appear on the tissue. Include any pertinent pattern markings, including grain line, notches, bust points, etc etc. Mark in the 5/8" seam allowances, and transfer in any pattern markings along the edge of the pattern. Be sure to clearly label the pieces.
4. Measure out from the pattern edges (NOT the seam allowances!) the amounts determined in Step 2. Redraw the edges. Use curve templates, it will make your work much easier! .
One method used to redraw the edges of a pattern is slash-and-spread. For this, you would make a copy of the pattern without seam allowances, cut each piece vertically (and horizontally if the lengths are also being altered) and simply physically move the edges of the patterns to the new location and retrace. I will demonstrate this method, as I am taking photos of my workflow.
5. Add on new seam allowances (I generally opt for 1/2" instead of 5/8"). Cut and sew a mockup; grading won't guarantee a perfect fit, so do at least one fitting to make any necessary adjustments. Once you are happy with the pattern fit, sew per the pattern's instructions.
This will take me all weekend. I am taking pictures, and will either edit the photos into this post as I go or create a new post.