It's time to seam up our Abrams and add the finishing touches!
This is where you're going to be very, very pleased with yourself for taking the time to block these pieces so beautifully, with crisp clean edges that make seaming a breeze. I'll walk you through the various seaming and finishing steps here. Instructions for these techniques are in the Handsome appendix, but I'll also link to other people's excellent photo and video tutorials at each stage.
First, join the shoulders with a three-needle bind-off.
Next, lay your front and back pieces out flat, and introduce a sleeve to the mix. The center of the sleeve's bound-off stitches should line up with the shoulder seam you just made, like so:
Next, join the sleeves to the body.
Thread your needle with a nice long piece of yarn, and you're ready to sew. Beginning at the edge of the Front piece, join the curved underarm of a Sleeve to the curved armhole of the Front using mattress stitch.
Once you've joined the short curved sections, you'll reach a long straightaway on both the sleeve and the armhole. Here, you're working with perpendicular fabrics. That is, the stitches of the Sleeves are at a 90-degree angle to the stitches of the Back and Front. Kelbourne Woolens has a great photo tutorial for invisibly joining perpendicular knit fabrics. If you prefer video, Wool and the Gang has this tutorial, which helpfully uses their massive fat roving yarn.
Once you reach the curved, shaped sections of the Sleeve and Back piece, just return to using mattress stitch. Now your sweater looks like mine does above.
Then join the Front, Back, and Sleeves together at the side seam.
Beginning at the bottom edge, where your provisional cast-on is, use mattress stitch to join the Front to the Back, then continue on to join the Sleeve seam all the way to the provisional cast-on at the cuff edge. For guidance, I think Staci's mattress stitch tutorial is a good one:
Tack down the bottom and cuff hem facings.
Next, you'll unravel the provisional cast-on and tack down the released live stitches at the hem and both cuffs. I like to fold the hem facing up at the turning row and pin or baste it in place before I start sewing. I tug on the provisional cast-on chain to release the stitches one at a time. As each new live stitch is released, I run my tapestry needle through it, without twisting. Then I run the needle, from bottom to top, through the nearest purl bump on the back of the sweater fabric and pull the yarn through. Working through the purl bumps allows you to follow a straight line, so that the hem facing will lie flat.
Finally, add a neckband.
Here's a quick video tutorial from Berroco Yarns showing two different methods for picking up stitches around a neckline. I prefer the first method -- the ridge that it creates on the inside will be covered by your neckband facing when you turn it inward and tack down the live stitches as you did for the hem and cuffs.
I like to give my seams and hems a good heavy steam with my iron, then gently press them flat with my fingers.