Guys, it’s going to be a long, long winter unless I can think of something to talk about that’s not secret! I’m still frantically knitting over here, and getting more and more excited about my upcoming trip to Rhinebeck. I’m teaching two classes on Saturday, and I’m a square in the always-fun Rhinebeck Bingo, and staying in a great house with my bestest buds. Couldn’t be better. Seems pretty likely that you won’t see me again until I return from the festival…
…So until then how about a little bit of technical talk about sleeve caps? Anyone who has taken my class knows that I’m pretty fanatic about set-in sleeves and sweaters done in pieces. Seams are magical things, transforming this stretchy, sometimes unwieldy, with-a-life-of-its-own fabric into a structured and well-fitted garment. The number one response I get to this opinion is that everyone hates setting in sleeve caps and they never come out right.
So I thought I might share how I do them. I took some snapshots of the latest sweater I put together (sorry, can’t talk about it yet) with the intent of walking you through the process.
The first thing to recognize about sleeve caps is that some modifications to your sweater will cause them not to fit. The length of the curve around the top of the sleeve cap must be the same as the length of the armhole length on the front and back combined (within an inch, say). So if you change the armhole depth, or your row gauge is off, your sleeve caps might not fit.

That said, here’s how I go about things: First, I seam the shoulders and lay the body of the sweater and sleeve out as shown. Then, I use openable stitch markers
to pin the center of the sleeve cap top to the shoulder seam, and to pin the edges of the sleeve cap to the armhole shaping edges:

The stepped bind-offs at the armhole edge should match the initial bind-offs on the sleeve caps for most sizes (in some plus sizes, the second bind-off on the armhole is much longer than it makes sense to use on the sleeve cap. The first bind-off should always match exactly.) So next, I pin those:

I then ease and pin the rest of the sleeve cap together, about every inch or so, all along one side. I pick the whole thing up and lay it flat, checking my work on the first side.

Repeat for the second side, and lay the whole thing flat. You’ll notice at this point if there’s any weird puckering or anything else you need to adjust. (If your sleeve cap doesn’t fit exactly, this is the point at which you should spread the discrepancy in length evenly over the whole cap for the best chance of a smooth finish.)

Then, it’s time to seam! I use mattress stitch. When I’m knitting the sleeve cap, I always make sure to do my decreases 1 st in from the sides. This gives me a nice even edge all around. Typically I use a long tail from my sleeve cap bind-off to seam the edges and start at the top of the cap. This sweater was knit in tweed, though, so I needed to use a separate smooth yarn for seaming. So I started at the underarm bind-offs.

I work about an inch of mattress stitch at a time, loosely, and then pull everything snug. Repeat carefully all around the sleeve cap, making sure you keep the fabric even with the pins.

And that’s basically all there is to it! The only thing with mattress stitch is that you need to make sure you’re keeping the same number of stitches inside the seam at all time–that is, don’t jump “columns” of stitches when you’re seaming. For horizontal fabric, go under the “V” of exactly one knit stitch. For vertical fabric, make sure to pick up only that little bar:

If you take it slowly, the seaming shouldn’t take much more than an hour per cap. And given the way set-in sleeve sweaters fit, that’s a totally worthwhile investment!
