Many ladies like to go to a print shop and print the patterns up to scale, but I've been doing mine at home. It takes a bit of time, but not a lot, and it isn't that hard. The books themselves suggest to draw out a grid on paper and then transfer it, but I tried that and it takes forever just to draw out the grid! I think I spent an hour using that method just for the front bodice piece. The method below is my own.
You will need:
-A fairly large quilting mat.
-A long ruler; I use a quilting ruler that is 18''x3''. A yardstick could potentially work, but a normal 12'' ruler would be too short.
-A roll of see-through plastic tablecloth; the kind that is used for parties and cut to the table size, then thrown away afterwords. It is imperative that it is see-through, that is what makes this process so easy!*
-A couple weights, or anything heavy that happens to be nearby (a candle, the Bible, a mug of coffee, which wasn't a good idea....)
-A permanent marker, and a normal old pen
-The pattern you wish to scale up!
My adorable dog, who likes to supervise.
*Now I am going to talk about how much I love this stuff. I bought a big roll at Zurchers for around $10, and it is the best thing ever! Not only can it be manipulated like fabric on a dress form, but it is see-through, which is a great advantage in doing scaling work. It also stores better than paper, which creases and rips. This doesn't really rip, but it can stretch if pulled too much. I actually tried to sew with it like a mock up, but the feed-dogs on my machine didn't like that.
Before I begin, there are certain pieces which I don't bother with. Usually, this means skirts, especially if they are just rectangles sewn together. Even if it has a train or the like, I know that it probably wouldn't be the right length anyway, so I just go ahead and mark the circumference and occasionally length of the skirt somewhere on one of the other pattern pieces. Complicated draping on bustle skirts might be the main exception, or some of the really fitted skirts in the 2nd volume.
To start, spread out your plastic roll onto the mat and put a couple weights on the corners. Match up the edge of the plastic so that it doesn't butt up directly to that line but a little past it.
If there are any straight lines on the grain of the fabric, like center front or back, start there and use your ruler to keep it neat. You'll work off of this line. Use the normal pen, because later we'll use the permanent marker to darken the final lines. The particular pattern I'm scaling today is a 1770-1780 bodice. Most of the dress in the 1700's are pretty easy, because the very front is straight. However, the front on this one isn't on the grain, so I'm going to start on the bottom.
To draw the rest of the confusing curves, there are a couple different ways to do it. 1, mark it slowly square by square, or 2, mark dots every so often and connect them with a smooth curve. Below, I'm doing a little of both at the same time.
I usually pay attention on the grid to where the lines go through the square. Mentally, I'll mark it either as 1/4'', a hair to either side of that, or right from corner to corner, etc. Take advantage of the little dots within each square inch on the mat.
Here, I've come to where I'd rather not mark out every single line, so carefully counting out the squares I made a reference point at center front. I'm just going to 'wing it', so to speak. Isn't my way of drafting great? Maybe that's why I have to spend so much time mocking up...
Good enough, says the sewing demon within me.
On all the lines that are straight, but aren't on the grain, I like to work completely around it until the end, and then use the ruler to connect them.
Outline the finished product in permanent marker so that any lines that you may have had to fiddle with to get straight don't mess you up later.
Remember, the Janet Arnold patterns don't have seam allowances included, so when cutting out the pattern to store, allow a couple inches all the way around for some flat drafting. Of course, I should take my own advice, since I messed up and there wasn't any on the side seam in the end. Don't forget to also add grain arrows to keep it all neat! To store them, pin all the pieces together and date them so they don't get mixed up.