What's funny is sometimes on a smaller tree I have to use a little sloped backcut(aka farmers cut) just to get a bore cut that won't nip the back all the way thru. We call it a triple helix then .Prolly a Michigan thing. I'll bet it don't even come close to a good farmer notch.
Here's the one I did on the cottonwood this week, it's actually called a step cut.What is this double helix back cut you speak of? Ive never heard of such sorcery!
Looks like it works for me, just like hooked on phonics .