So you've got two sleeves and a body all knit up for your steeked jacket, and now it's time to join the three pieces together and knit up the rest of the body.
Get out your 100% figure - the number of stitches you cast on for the body - that I told you to write down. You need 8% for the underarm stitches.
100% body figure x 8% = the number of stitches for the underarm.
On my jacket, that comes to 18 stitches.
So I put those stitches on a holder (in my case waste yarn, but you can use an actual stitch holder too, if you want) at the underarm of the sleeve, where the beginning of the round was, and where all the increases took place:
Do the same on your body stitches - put 8% at each underarm on waste yarn or a stitch holder:
You can kind of see the vertical stripes I put in at the sides to make my jacket fit with the pattern repeats. Sorry the photos are blurry -- no idea how that happened. (Except that my photography skills suck.)
These stitches are at the armpit, anatomically speaking, of your jacket. Later they will be grafted together, and I'll show you how to fudge the pattern a bit to make it less noticeable. This is a hallmark of Elizabeth Zimmerman seamless patterns and found in most of her groundbreaking construction methods. At this stage, where you've got the whole thing knit to the arm pits, you can choose to knit a wide variety of shoulder types; yoke, raglan, saddle, hybrid, etc. We'll be knitting her saddle shoulder version.
The stitches you take off should be centered in the pattern; take a look at the above photos. You can see that the pattern on each side of the on-hold stitches ends at the same place. To make it fit, you can add or subtract a stitch and it won't make much difference, but the stitches on hold for the body and the sleeve have to be within one stitch of each other. (For example, if you've got 20 sleeve stitches and 21 body stitches, you can graft them together later with little trouble; if you've got 20 sleeve stitches and 25 body stitches, grafting is going to be a problem.)
Now. At this point you could just shuffle everything around until you've got your body and sleeves on one circular needle: front, sleeve, back, sleeve. And if you wanna do that, go right ahead. But having done this a couple times, I find I constantly drop stitches all over the place when using the Shuffle Method. When I do it, I knit the whole thing together, basically knitting on each bit as needed.
Please note, for the sake of clarity, that in the photos following, the body stitches are on a BLUE circular needle, and the sleeves are on a WHITE circular needle. And the beginning of the round is still the steek in the center front of the jacket.
If you're having trouble visualizing this, actually lay the pieces out on the floor in the anatomically correct layout. Note how the armpit stitches match up, and also how the stitches to be worked flow naturally across the front into the sleeves and into the back and on around.
From the center front, knit across the front of the jacket until you get to the armpit stitches that are on hold. Place a marker. Then knit the SLEEVE STITCHES from a sleeve onto the body needle:
You can see me knitting the sleeve stitches off the white sleeve needle, onto the blue body needle. To the right is a yellow bit of yarn I'm using as a marker.
When you've knit up all the first sleeve's stitches, place another marker and then knit across the back. (See now why I said having the body and sleeves all on the same pattern row for this was important?) When you get to the other arm pit, where the other stitches are on hold, repeat the process; place a marker, knit the sleeve stitches onto the body needle, then place another marker, and continue on to the front.
There you go. All joined up and ready to rock.
Work a few rows in pattern with no decreasing, up to two inches/4.5 cm worth, adjusting where you are in the pattern as you skip between body and sleeve. These non-decrease rows determine the depth of the armhole - the more rows, the deeper. Deeper armholes are generally more comfortable. However it also adds to the sleeve length.
Next, the shoulder decreasing. I'm knitting as fast as I can so I have example photos.
As always, feel free to e-mail me with questions.