There's not really a whole lot in the way of explanation and pictures to this post, but don't be fooled - this step is time consuming! It's a rare occasion when I get a sleeve inserted perfectly the first time. It's not uncommon for me to have to unpick and re-sew sections of the sleeve insertion seam twice. But you really don't want this area of the jacket to be sloppy if you can avoid it. The shoulders and lapel are the focal point of a blazer. So slow and careful work is the motto of the day.
The pictures I took for this post are from the insertion of the first sleeve on my jacket, and I did indeed have to unpick parts of this one. On this sleeve I basted the seam after pinning it, and I found that I had much better luck on the second sleeve when I skipped the basting and just sewed the pinned-in sleeve. So you may want to try both to see what works for you, or stick with what you know if you have a method you like.
When you pin in the sleeve, you will of course match up all the notches and dots and then distribute the ease around the cap as evenly as you can. I mentioned in the last post that I have more luck with this when I bring that easing down beyond the dots by 1" or 1.5".
When sewing the sleeve in, place the work so that the inside of the sleeve is facing upward and the garment side is down, against the foot plate. This time I also used a clear foot to help me see any puckers that were forming. Instead of starting and stopping your seam at the underarm, start and end at the notch to the left of the underarm. On one sleeve this will be the front notch, and on the other it will be the back notch. Avoid the temptation to sew the sleeve in on the free arm with the garment side up! Your finished product will be nicer if you follow the above instructions :-)
Once you've sewn the seam, check it from the outside to make sure you don't have any puckers. If you do, unpick that section and do it again.
When it looks as nice as you can possibly get it, sew a second line of stitching from notch to notch at the underarm, 1/8" inside the seam.
Trim the seam allowance between the notches next to this second line of stitching, but leave the rest of the seam allowance. Keeping the seam allowance around the top of the armhole will contribute to a nice structure at the top of the sleeve. Now take the jacket to the ironing board, and from the inside, press the seam allowance only, extending onto the sleeve itself by no more than 1/8".
Take your sleeve header and fold it in half to find the center. Pin that center point to the shoulder seam inside the sleeve, lining up the edge of the header with the edge of the fabric. Then pin the sides around the armhole. I extend mine down to where the princess seam is in front and a bit lower than the princess seam in the back. Stitch the header to the seam allowance by machine just inside the sleeve insertion seam.
Then trim away the excess from the ends by cutting away a curve. Note that with these ready-made sleeve headers, the muslin piece (the longest part) is against the outside of the jacket and the fleece toward the inside. If you've made yourself a shaped sleeve header as I showed in the pattern pieces post, insert it in the same way - the edge of the header will line up with the edge of the fabric.
Now take your shoulder pad and fold it in half as well to find the center points of both the straight and curved edges. These points will line up with the shoulder seam. Align the straight edge of the shoulder pad with the edge of the fabric in the armhole, just like you did for the header. Then stretch and pin the pad around the armhole. You need to stretch it as you insert it because you'll be inserting it in the opposite curve to how it will be worn on the body. You can pin it in place and try the jacket on to check the placement if you like. But I usually don't - the shoulder pad is just getting tacked to the armhole seam allowance with a running stitch, so it's easy enough to undo and fix if it isn't inserted smoothly. (I've scratched myself with pins too many times while trying on my jacket - I now prefer to just sew the shoulder pad in from the get-go!) Tack in the pad with a firm yet not tight stitch.
Once your shoulder pad is in a position you like at the armhole edge, pin the marked center on the curved edge to the shoulder seam. Most instructions I've read say to catch stitch the pad to the shoulder seam allowance but I find this to be very fiddly. Instead, I like to stitch in the ditch by hand from the outside. The shoulder seam will be deeper than the other seams because of all the canvas and muslin and the fact that we didn't use the clapper on it, so these stitches won't show at all. I use what is basically a pick stitch here.
I feel the need to add that although it looks like my sleeve cap is puckered in the picture above, it is not! It looks like it though because I've pushed the sleeve and pad down in order to be able to stitch in the ditch. Here's the real deal after it's all put together:
I'm really happy with how these sleeves went in - for my purposes, removing the extra ease was the right decision.
And now the outer is complete! Next we'll be moving on to constructing the lining, and we're not too far from putting the whole jacket together!