Almost all sewing is a complex combination of manual dexterity and the sewing machine capabilities. When sewing a narrow hem on a dress, often times a bridal or prom dress carefully look at the hem. Inspect for the amount of curve in the hem. If the hem is mostly straight, you should be able to sew the hem using your hands properly and combining short bouts of sewing with short bouts of realigning. This technique explained assumes a right hand dominant perspective but if