Originally Posted by
JenniePenny
I square them up by putting the 45 degree line on my ruler on the seam line of the sewn units. Then use the right edge of the ruler to cut.
I realized there is more I could have written to make it clearer to a new quilter:
After making the first cut, then turn your fabric unit so that the cleanly cut edge is on the bottom of the unit. Put this edge against a horizontal line on your ruler. Trim up the right edge.
Turn your block again so the newest cut edge is on the bottom and line it up with a horizontal line. Trim up the right edge.
Repeat once more. You have to do all four sides. That is the reason a rotating cutting mat was mentioned. It is very handy.
But to begin the process, use the 45 degree line of your ruler on the seam line.