I've spoken with independent pattern designers in the past, and many use a similar process for pattern design though everyone has different techniques.
My college spread technical design into a few courses, some being Computer Patternmaking and Production Systems. From all my notes, it appears I took at least one of these courses in 2006, so perhaps my information is dated.
My old binder for Computer Patternmaking in 2006. Yup, liked vintage fashion even then!
In the industry, there is an absolutely completely different system for importing your patterns into the computer (a giant table where you apply grade rules to each point of the pattern). After the blocks are imported, your computer then goes by whatever rules you set up to grade the pattern by, known as a rule table.
Photo of my old rule table.
This makes it super easy - you just apply the points to the pattern pieces and then BAM the computer spits out a perfectly graded pattern for you (that is, unless you apply the wrong grade rule).
My graded patterns from school. A few months ago, I was trying to figure out a way import grade rules to Illustrator for fast pattern grading, but I kinda gave up. I am assuming you can "create an action" that essentially corresponds to how you will shift your pattern coordinates, but I haven't finished and applied this idea.
Now, without these machines that cost thousands and thousands of dollars, the process is a little less straight-forward. Almost everyone I asked who does PDF patterns uses Illustrator -- it's a relatively kludgy program with lots and lots of buttons and options and might be more confusing than flying a plane, but if you like technical design and the computer, you will get a hang of it much easier than I did.
So how do I get my patterns into the computer?!
I make all my patterns by hand, so this is a good question. There are a few ways of getting this accomplished: One way (the first way I did it) was make a copy of my master pattern for the Petra Dress and then cut up the pattern, scanning piece by piece full size into Photoshop.
I then re-attached the pieces (one by one, yes) and made them each into a pattern piece in the computer. This is tedious, but still very accurate.
Someone else mentioned having a giant scanner that you feed pattern pieces into and then grading from there, but I wasn't able to buy a giant scanner at that time of my life. This may be helpful for some people out there.
The third way I've learned is that you can import your pattern blocks into the computer. Yes, you can digitally draft your blocks into Illustrator! You will need to turn on all of your line measurement tools and from there, you can plot the correct length points. I am, by my standards, an Illustrator idiot and I found this not so difficult to do. You need to take some time to master the controls, but once you do it seems like a breeze.
This video shows more or less how I digitized my patterns in Illustrator.
How do I create patterns in Illustrator?
Using your imported and saved blocks, you can essentially use real-life techniques like slashing and spreading to create your actual sewing patterns. I don't really know in-depth the controls to use, but I do know it's important create a copy of this block, manipulate that block, create a new layer and then trace over your manipulated pattern pieces to create a new pattern piece, much like in real-life. There are probably a few video links on YouTube, but as of writing this post I haven't found anything super-helpful for you guys.
Is Illustrator accurate?
People have asked me this, YES! Illustrator is very accurate. Many people use this program for many other technical drawings aside from drafting sewing patterns. As long as you have all your measurement tools turned on, then you should be fine as far as accuracy goes.
How do I grade my sewing patterns in Illustrator?
This is something I'm still working on figuring out completely, but I have seen a few ways of doing it. One way to do it is by literally moving the end points of each piece around the designated amount it needs to be adjusted. From my understanding, this may not be accurate enough because you want the amount you're grading by distributed throughout the entire pattern, not just on certain points. But maybe I'm wrong since there was a book I used in person a while back that just shifted the points on a pattern using the connecting lines of each pattern piece. See this video for one way of grading a pattern.
One of the other absolute best ways I've found that has helped me understand pattern grading is this post by Threads. It helps to become familiar with this in real life before trying to apply it to Illustrator. When I was working on my PDF pattern, I actually did cut and spread my sewing patterns based on the guidelines from this post while in Illustrator. I personally use a 2" grade rule, meaning the size difference between each garment is an evenly distributed overall 2".
You do have to figure out some simple math - dividing fractions - for this, but the Threads article is really good at spelling it out for you.
I did buy a pattern grading book online but it's more geared toward industry pattern grading. While I think it might be helpful for me to figure out how much to shift pattern pieces by on certain garments, I'm not sure I am reading what it's telling me correctly. I'm sure with a little bit of patience and playing with it, I can figure it out.
Ok, I designed and graded my patterns, now what?
You're going to need to learn how to tile your patterns onto multiple pages.
From there, that's really it. You will want to create cutting layouts, specify yardage for sewing (I've made a marker before in Illustrator), type out sewing directions, and any other necessary construction techniques. It could also be helpful to make a sheet of all pattern pieces included with numbers on them so your customers know which pieces are which. You will also need to make a key showing which lines are each piece. This is usually done in Illustrator with varying dashed lines corresponding to a certain size. Also, make sure your customers know which notions to buy like zipper sizes, buttons, etc.
If you are using the digital patterns solely for yourself, you can skip all this extra work!