Set-in sleeves are kind of tricky, and there is an easier method.
This method is still good to know, because you might find yourself in a situation where you want to modify/add sleeves to a top that already has the side seams sewn up, or doesn’t have side seams.
Here we go. We’re starting with the side and shoulders seams already sewn, so we have a basic sleeveless top. The sleeves have also been sewn up and cuffed.
You can ignore the hood in the bottom right hand corner. That’s for later.
Attaching set-in sleeves (the easy, cheater way).
Okay, so it’s not really cheating. It’s a perfectly legitimate way of attaching a sleeve, and it is way easier.
However, a set-in sleeve is a set-in sleeve because you’re supposed to be setting it in, and with this method, you don’t.
Anyway, I’m splitting hairs.
Keep in mind, though, that this will only work if you haven’t already sewn up your side seams. If your side seams are sewn, you’ll either have to cut them open, or use the other method.
And if your garment doesn’t have side seams that line up with the sleeve seams, you’ll also have to use the other method.