They work, but you will need to apply a good amount of pressure also or they may slip, which may be your problem when cutting. WHen I have had problems, I amke sure to mark the place on my ruler that I need to line up, with tapes that are made for that purpose or regular masking tape will work. Then make sure you are applyihng enough pressure with the ruler had to keep the ruler from shifting. Even a little bit will throw you off. Also make sure you are using the rotary cutter right. It needs to be held so the blade is at a 45 degree angle to the mat and fabric.