Most sleeves are designed to be slightly larger than the armholes. This helps make the suit sleeves more comfortable, and gives you freedom of movement. However, it also requires you to ease in the extra sleeve fabric. You can do this by carefully pinning and sewing the sleeves to get a smooth, professional look.
Sew Sleeves to the Suit
Sew the front and back of the suit together along the shoulders and sides. Leave the body of the suit inside out.
Fold the sleeve right sides together. Pin the edges of the underarm together, then stitch the underarm seam using 5/8 inch seam allowance, or the seam allowance recommended in the pattern directions. Turn the sleeve right side out.
Insert the sleeve into the suit, lining up the upper edge of the sleeve with the edges of the armhole. Line up the seam in the underarm of the sleeve with the seam in the side of the suit. Line up the midpoint of the top of the sleeve with the shoulder seam.
Pin the sleeve to the armhole. If the sleeve edge is larger than the armhole, ease in the extra fabric by including a tiny amount of excess sleeve fabric in each pinned area. Do not leave any gaps or folds in the fabric. If you wish, you can baste the sleeve to the armhole using 1/4 inch seam allowance to help hold it in place.
Stitch the sleeve to the armhole using 5/8 inch seam allowance, or the seam allowance recommended in the pattern directions. Turn the suit right side out and check the seam to make sure there are no puckers in the fabric. Remove stitches with a seam ripper if needed and sew the seam again.
Sew the other sleeve to the other side of the suit the same way. Attach the sleeve linings to the suit lining the same way.
Hem Suit Sleeves
Try on the suit to make sure the sleeves are about 1 inch longer than you want them. Trim off any excess fabric if needed.
Turn the outside fabric of each sleeve end over 1 inch toward the wrong side of the fabric. Press the folds flat.
Turn the lining fabric at the end of each sleeve toward the wrong side of the fabric, just the slightest amount more than the outside fabric. Press the folds flat.
Thread the hand sewing needle and tie a knot in the end.
Whipstitch the sleeve fabric to the lining fabric, taking care not to stitch through the outer layer of sleeve fabric, so that the stitches won’t show. Tie a knot in the thread and clip off the thread just above the knot.