I have bought 2 different ones and although they cut ok with one layer, if I try to cut multiple layers, I have to go over the cutting line over and over, sometimes pushing so hard I about get calluses. Am I buying the wrong kind of rotary cutters? Also, are they supposed to spin as you cut? mine do, and when I tighten the wheel, it works its way loose again... sigh* not even sure i'm doing it right. Please help. :cry: