Sorry for the delay in response. This is actually not an uncommon issue with machines and zig zag stitches and it doesn’t always have to do with thread tension. I usually see this issue myself when sewing with lightweight knit. It usually means the fabric doesn’t have enough stability so the stitches start to pull the fabric towards itself. I suggest using a stabilizer in the area. If you’re fabric is washable, use a water soluble stabilizer that washes away after you finish doing the stitches. You might also want to do a narrower zig zag stitch instead of a wider one, if you can. Hope that helps.
professorpincushion.
aileenm
professorpincushion