I cut my borders lengthwise cuz I really don't like to have joining seams in borders. I have an 81" table that I lay the fabric out on, folded selvage to selvage. I slide a 24" cutting mat under the fabric along the edge I'm cutting and use my 24" ruler. If I need more than 81", I carefully slide the fabric down and continue the cut. Cutting that way, there's no risk of elbows from folds and I cut the two side/end borders at the same time.