With the 1940's pattern I am lucky because all the sizes are correct apart from the bust, which is 2 inches too small. In this post I'm going to describe as best I can how I correct the pattern pieces for my size.
When I first started making clothes pattern grading was always a massive headache, but I've finally, after a lot of trial and error, found a method that works. The book I use is Concepts of Pattern Grading by Kathy K. Mullet. It describes the basics of grading and has great diagrams that show you where you need extend or reduce the pattern so it stays in proportion. I don't actually use the same method of pattern grading as described in the book, but the diagrams are very useful.
For my dress I need to increase the bust by 2 inches so I will be using a 2 inch grade rule for this post. If you need to alter your pattern by a different margin I highly recommend buying the book to see other grade rules.
I have made my own diagrams so sorry for the bad drawings! They look complicated but will become simple - I promise!
WHAT YOU WILL NEED:
Clear sticky tape
Grade rule diagram
The front bodice......
I have split the grade diagram above into 7 different sections to make it easier to explain and transfer what I'm doing to the actual pattern. This is a basic bodice which doesn't look exactly like my pattern but the points and sections are still the same and the same rules will apply. In my case I only need to alter the bust so I will need to alter 4 pieces; 2 for the front bodice, 1 for the back and the sleeve. For this post I will be going through how I adjusted one of the front pieces.
STEP 1: Stick together enough graph paper so can you fit the front pattern piece on completely with the center front along a straight edge. Then pin the pattern piece to the paper and trace around the edge making sure to mark notches and circles.
STEP 2: Remove pattern from graph paper. Using the grade diagram above label key points on the pattern from A through to G. I don't have a dart on mine so left out F.
STEP 3: Now we are going to take each point and move it accordingly. I am only adjusting the bust on my pattern so will not be moving E or G, but if you need to you on your pattern just follow the same principle. To make it easy to see what I'm doing I marked the lines from the grade diagram on my pattern. It looks a little distorted because I actually have gathers in my front section. For your pattern you should be able to do a similar thing paying attention to key points on the pattern compared with the grade diagram.
This is where the graph paper comes in, when moving points use the grid on the graph paper to keep points in line. For each point you need to look at the lines below and to the right and move it according to the amount shown on the lines. I will go through each point so you see what I mean. All measurements are in inches.
Point A - has no lines to the right so doesn't move in that direction.
- has one line below it labeled 1/8 therefore it moves 1/8 upwards. (If you were decreasing the pattern size point A would move down by 1/8)
Point B - one 1/8 line to the right so moves left by 1/8
- two 1/8 lines below it so it moves 2/8 upwards
Point C - two 1/8 lines to the right so it moves left by 2/8
- two 1/8 lines below so it moves upwards by 2/8
Point D - two 1/8 lines and one 1/4 line to the right so it moves left by 1/2
- one 1/8 line below so it moves upwards by 1/8
STEP 4: Join the dots! I usually use the originally pattern piece here to get the shape right.
STEP 5: Mark on all the notches and circles and your graded pattern is finished!