But when it comes down to trimming hand-applique blocks, I prefer to be safe than sorry. Especially when I am trimming down to an unusual size for which I don't own a plexiglass ruler.
Even though I still have handful of Sue Garman's "Afternoon Delight" applique blocks yet to stitch, I just could not wait to start trimming them to the unfinished size of 7-1/4 inches square.
I have a 7-inch and 7-1/2-inch commercial ruler, but no 7-1/4-inch size. I made my own plastic template with lots of drawn lines to make it easy to find the center and line up the corners.
Because I have a tendency to slip when rotary cutting (especially when I am nervous trimming hand applique work), I got the template where I wanted it, then piled on my vintage pattern weights (I use them on the commercial square rulers, too!!).
Then, I draw around the template with my ultra-fine sharpie (or a Pigma pen).
Next I cut out my block using scissors to the inside of the ink mark.
Ta-da! Yes, I know slicing and dicing with the rotary cutter would have been quicker, but I am completely confident with this method. I typically watch movies or TV while I am working, and it is easy for me to make a terrible rotary mistake while trimming. This old-fashioned, but sure method keeps me from hopping around the house, swearing...