D, not sure what You're using to cut them, or how You're using it, but... You may be sliding a blade, slicing, possibly with the tip of a blade. If that's the current method, and You're wanting a controlled, straight line, try using a razor blade, set the blades sharp edge (not the tip/point of the blade) along the intended cut then press the entire blade straight down. I have a few modifications I cut this way and it works well for a straight and precise cut.