Butterfly sleeves are an elegant and feminine addition to a sleeveless shirt. They are referred to as butterfly sleeves because their wide bottom and gentle gathers resemble a butterfly's wings. It is best to make these sleeves from a fabric with a lot of drape such as a jersey knit, chiffon or silk. However, you may use any type of fabric giving the sleeve a slightly different effect.
Make a butterfly sleeve pattern from an existing basic sleeve pattern in your size. Cut out the sleeve piece and align the top seam with the arm opening of the shirt you wish to which you wish to attach the sleeve. Add or subtract seam allowance accordingly.
Draw a new sleeve pattern on fresh pattern paper. Place the new pattern paper over the existing sleeve pattern and pin securely. Trace the old sleeve onto the new paper making the required adjustments to the length and shoulder. Take note of any pattern markings such as the grain line, notches and suggested seam allowance.
Unpin the new pattern and cut it out. Pin it to a new sheet of pattern paper with one pin at the top of the shoulder seam. Draw seven vertical and parallel lines through the sleeve with one in the centre and the rest dividing the sleeve evenly into eight sections. Cut along these lines without cutting all the way through the pattern piece. Leave approximately 1 millimetre of space at the shoulder seam attaching the sections together.
Spread the sections apart evenly. The more you spread the pieces apart, the wider the sleeve. Pin the pieces down to the fresh pattern paper then trace around the new pattern outline. Re-draw any grain lines, notches and seam allowances. Re-test that the sleeve will fit into the armhole of your shirt. Make adjustments if needed.
Pin the pattern to your desired fabric and cut along the edge. Mark notches and seam allowances. Finish the bottom hem of the sleeve first, then turn the sleeve inside out and sew the underarm seam.
Attach the sleeve to the garment. Starting at the top shoulder notch, pin the sleeve around the perimeter of the arm hole making small gathers as necessary. If a lot of gathers are needed, unpin the sleeve. Sew a loose stitch along the top of the shoulder on the sleeve. Pull the threads gently to make gathers, then try pinning the sleeve to the armhole again. Sew the sleeve to the shirt. Remove any gathering stitches.
Sew the other sleeve in the same order. Complete the garment with seam finishes.
Tent and angel sleeves are similar in shape to butterfly sleeves, so look for these patterns as alternatives if you cannot find a pattern for a butterfly sleeve you like.
Setting in the sleeve is the most difficult stage. Pin the sleeve to the shirt very carefully to avoid unwanted puckers. Place pins perpendicular through the seam allowance about one-half inch apart. Do not sew over pins! This can ruin your sewing machine or break the needle.