I use a June Tailor Shape cut ruler all the time. With my Marteli Rotary cutter, I usually can cut 8 layers easily. Sometimes I can cut cup to 12 layers but have to press a bit harder.
8 layers is 2 pieces of fabric folded to fit under the ruler
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My newest Grandson, Caleb Austin, was born May 29th. I am now Grandma to 4 precious babies. I am so blessed!!!!