Friday, May 9, 2014
Quiltmaking 101 -- Seam allowances and sewing precision
Most quilting instructors make a big deal about quarter-inch seam allowances. They get all out of joint if people sew seams even a hair narrower or wider; they want you to buy a special quarter-inch presser foot to help you maintain this width; they might even make you measure your pressed seams and feel mortified if they're not exactly a quarter-inch.
I am not like that. I think seams should be approximately a quarter-inch, but I don't care if they're a bit off. What's important is that they hold together, aren't too bulky and are relatively straight. A quarter-inch seems to be plenty wide to hold up to the stresses of sewing and washing, and narrow enough to avoid a lot of bulk where seam allowances overlap.
It's probably helpful to be able to sew a uniform seam, for situations when you want your work to end up a certain size, or the same size as other pieces. If that's the case, then you can be confident that if your blocks or strips start out the same size (by accurate cutting) they will end up the same finished size after you've sewed a seam on each side.
The best way to learn to sew a uniform seam is practice. Find a landmark on your sewing machine that is approximately a quarter-inch away from the needle. Then sew lots of seams and take pains to line up the edges of the fabric with your landmark.
One last point about sewing: the stitch length. You want your stitches to be small enough to hold the seam together firmly while you work. There's a lot of manhandling and intermediate cutting and trimming that will weaken your seams if the stitches are too long. It's disheartening to inspect your quilt top after you've sewed it together and find seams popping open or even spread apart at the end.
But on the other hand, never make your stitches so short that you can't get a seam ripper easily into a stitch. You will have to rip the occasional seam; that's a promise. My sewing machine automatically goes to its default stitch length of 2.40 mm when I turn it on, and that's pretty good for ordinary piecing. If I know I will be doing a lot of intermediate cutting -- for instance, making strip sets to be sliced into narrow rows -- I make the stitches a bit smaller to keep the seams from coming apart,
The right size
You may be thinking, if it doesn't really matter how wide my seam allowances are, how will I get my blocks to be the right size? I respond, the "right size" is whatever size you end up with.
Let's say we both start with a pile of two-inch strips. We decide to make square blocks with four rails. I sew four long strips together, press my strip set carefully, and measure it at 6 1/4 inches across. Meanwhile you sew and press your strips, and measure your pieced strip set at 6 3/4 inches across. (Apparently I'm sewing a bit wider seam allowances than you are.)
I would probably decide to trim my blocks to 6 inches square, and you could trim yours to 6 1/2 inches. Your quilt would end up a couple of inches bigger than my quilt, and that's OK. It doesn't matter whether the blocks are 6 inches square or 6 1/2 inches, or if the quilt is 58 inches wide or 60.
(Why don't we each trim our blocks to exactly what the strip set measures? Why are we wasting all that time and fabric making the blocks smaller than they need to be? Good questions. Just because the first strip set ended up to be a certain width doesn't mean that every one I sew will be identical. Nor do I want to spend the time and effort to be that precise. I'd rather give myself some wiggle room and trim off a bit from each block than end up with 32 blocks measuring 6 1/4 inches and 4 blocks that are only 6 inches.)
By contrast, if you're fixated on making a block that will finish to 6 inches, you can spend a lot of time fussing over precise cutting and precise seam allowances and still wind up not exactly the right size. Why give yourself that grief? I'm an advocate of "sew first, cut second."
In other words, always start with a piece of fabric a little larger than you think you will need. Even though mathematics tells you that four 2-inch strips, sewed together with quarter-inch seams, will measure 6 inches across, we're working with fabric here, not precision-milled pieces of steel. Unlike steel, fabric stretches, it gets off grain, it changes its size while your back is turned. So give yourself a break. Make your strip or your block a bit too big, then when you're done sewing, trim off anything extra.
And never trim to the final, exact size before you have pressed your blocks or your strip set. Careful pressing will often cause a block to get as much as an eighth-inch bigger as you get all the slack out of the seams and make the block lie flat. So don't bother trimming to size before you press; you'll just have to do it all over again afterwards.