I can’t really afford many pre-cut mats for my watercolors, so I bought an inexpensive Logan cutter and some matboard, etc. I have had a few successes, but aside from my arthritic fingers, I can’t seem to keep my straight edge from slipping, however careful I am.
I use either a metal carpenter square, or a steel ruler with a cork backing, but manage to shift the straight edge every time. It wouldn’t be so bad if I didn’t need to make at least 3 cuts to get it done.
I am careful to change blades and follow the directions and all but I still manage to ruin too many of them.