Making a shift dress in rayon challis. The zipper tape sits flat but the fabric either side ripples along the whole 40cm. I have basted first, used the invisible zipper foot, and stitched both sides from the top down. It looks fine flat on the table and terrible on the body.
Also check whether that seam is cut slightly off grain. On a challis that drapes this much, two degrees off is enough to produce exactly what you describe, and nothing you do at the machine fixes a cutting problem.
Lay the piece flat and follow a single crosswise thread from the seam to the fold. If it wanders away from the seam line, it was cut off grain.
How do I check that after the fact, short of unpicking the whole seam?
Let the dress hang for 24 hours before you insert the zip. Rayon grows, and if you sew it fresh off the cutting table the zip side becomes the short side.
Baste with a water soluble glue stick rather than pins. Pins let rayon shift about a millimetre each and it adds up over 40cm.
@muslin_mira · 8mo ago · 2 replies
Stabilise the seam allowance before the zipper ever touches it. A 1.5cm strip of lightweight fusible interfacing cut on the straight grain down each side of the opening, and the ripple stops. Rayon has almost no recovery, the zipper tape is essentially stable, so the fabric stretches to match it during sewing and then relaxes afterwards.
Good news is you already stitched both sides the same direction, which is the other classic cause.
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@barre_chord_blues · 8mo ago
So at least I got one thing right. Interfacing strips on the next one.
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