Well, it’s not too hard to sew straight to the corner,then turn and sew straight to the edge. Even if the cover doesn’t fit to your liking, straight edges are much easier to alter than the dreaded CURVES. Now I’ll show you a method for making the curves in your cover bend straight.
After carefully draping and centering the main cover fabric, take time out to trace the backrest curve onto paper. I placed the paper’s straight edge exactly on the straight seam along the back and ran the pencil in the ditch of the curved seam toward the front of the chair. Check your curve’s accuracy in front of a window to take advantage of the sun’s light box effect.
Pull the front cover tightly toward the chair back. Meet the front and back pieces at the upholstery seamline and pin in place. Continue pinning along the seamline until entire back is encased in cover fabric. Pin both side seams from seat base to the end of curve before removing cover from chair .
Grab each top corner of back cover and pull straight up to remove your cover from chair back. It won’t come off easy. The fabrics will tend to stick together, so pull carefully or you will need to re-pin the seam.
Place the corner pattern you drew on the seamline, NOT the edge of fabric. Use fabric marker or pencil to trace the curve of your seam right on the pinned line. Sewing accurate curves while easing is nearly impossible without a guide. The line helps so much and your cover will fit better.
Re-pin your seam perpendicular to the raw edge so you can stitch right up to the pins before removing them. DO remove all the parallel pins. They will damage your fabric, your machine, and maybe you – if you sew over them.
This pinning can be tricky because you will need to EASE the fullness of the curve. Sew with the most fullness against the feed dogs to assist your easing. Also, you can stitch as the yellow line indicates on the un-wonky portion of your seam until you reach a very bumpy section. With your needle DOWN [see arrow], straighten fabric and arrange fullness behind the needle before continuing on.
This is easier than it looks in the picture!
Turn cover right side out and try it on your chair. CHEER! when it fits.