I'm glad you had your aha! moment (but how frustrating in the meantime). I agree that tools (and fabric) really do matter. I had a rotary cutter that was always catching on the sides of my rulers. I bought a new rotary cutter for a completely different reason, and I've never had that problem with the new one. Don't know why it made a difference, but it sure did, and now I'm not ruining my rulers by nicking them.