on the bias
In sewing, following a diagonal line across the grain of the fabric, especially one running at an angle of 45 degrees. OK, class. The first thing to do is to cut the fabric on the bias. Be sure to make your stitches on the bias.
on the bias
on a diagonal line; on a diagonal pathway or direction. The panels of the dress were cut on the bias. The seamstress sewed the fabric on the bias.