When cutting covering with a straightedge I actually prefer to cut with a single edge razor blade. I feel I have better control over the blade than I do with the X-Acto blade. In fact, when I'm working with covering I do about 95% of cutting with razor blades. Here's a tip. Buy them 100 at a time, they are cheaper that way. You can pick them up at Lowe's/Home Depot/Menard's or the like. When you are cutting as soon as you feel that blade start to "snag" throw it out and break out a fresh blade. A sharp blade is probably your best friend when working with covering.

Here's another pointer that I like to put out, and it deals with disposing of razor blades. I used to just throw the blades away until one day I was putting out the trash and I noticed a blade that I had thrown away cut the trash bag (or course spilling everything out). I started to think that could have been my hand picking up the bag, a neighborhood pet, or even the guys that pick up the trash. So I came up with a better way of disposing of them. I took an old sour cream container and washed it. I slit the lid to put the blades in through and then sealed the container up with tape. Now when I change blades I simply put them in the container, and then throw that away when it's full. It lasts about 3-4 years for me before it's full. And yes, I change blades that often. I have 4 X-Acto handles that I use and I put fresh blades in all of them when I start a new plane. I also change out razor blades pretty often. On a 60 sized plane I would say that I use 10-15 blades during the covering job for that plane.

Hope this helps

Ken