You will need:
- Elastic (I used 4mm thick stuff)
- Unstitched sleeve pieces
- Thread in the colour of your fabric
1. The easiest stage to attach the elastic is after you've added any gather stitches to the sleeve caps but before you've stitched the underarm seams and sleeve hems.
2. Draw a line in chalk or washable pen vertically up the centre of your sleeve, marking the points where you want the gathering to start and end (I also marked these points with tailor's tacks). The starting point should fall at a point that will be enclosed inside the sleeve hem to keep things nice and neat. I started mine 1/2" up from the raw hem and ended 4 1/2" above this point.
4. Start sewing! You can use either a straight stitch or zigzag stitch. Begin at the hem, securing the end with a stitch and backstitch. Then sew carefully in a straight line while stretching the elastic up to the end point of your gathering. Secure at the top with a backstitch, then snip the threads and the extra elastic.
Et voilà! You can now stitch the underarm seam and hem and attach the sleeve to your garment.