This young climber wanted to rent my bucket truck a few weeks back. I met him just before dark to drop the truck off, but after seeing the job (in the side of a sledding hill) and the forecast calling for rain the next day there was no way I was goiong to let him drive that truck on the wet hill.. even though he thought he'd be ok because he had mats.
It was only the top of two trees, the second of which I could take in one cut.. so even though it was dark I said let's get this done and we set the truck up under the first tree. I got the offending branches cut quickly to where he could drop the rest of the tree, but was going to make it a little easier for him by taking another couple big cuts to get the side weight off when the cops showed up. So he explains why we were working that late to the cop (this is only a couple of weeks after the biggest storm damage anyone around here remembers). The cop says you can make one more cut. So I say let's get the top of that oak out... we reposition the truck and by this time it's pitch black. The oak was probably 90' with a good bit of front lean to an open DZ for 60 feet. No worries at all about directional control. I went up to just below the first big crotch and made up a cut on the spot.
I call it the box cut...
Cut a level undercut about the same distance as would be used for a standard notch (say about 1/3 diameter)
go to the far side of the tree and make a side cut in the same plane (perpendicular to the first cut) again about 1/3 diameter)
then do the same on the near side... so there are basically three sides of the tree cut about 1/3 of the way with the only uncut wood on the backside.
then just start cutting from the back straight in and cut til the wood pops.
It worked perfectly...
Now this was pretty sturdy wood grain and just below a crotch, with not toooooo much front lean, so the chances of BBC were reduced. I wouldn't have used this cut if the chances of BBC were much more than they were.
One of the things I had to explain to the experts on this forum (which Burnham clearly didn't understand) is that the reason the coos bay is so effective at preventing BBC, si not because it allows the faller to race through the cut (as B thought), but because you have effectively reduced the amount of intact fibers between the trunk and the top to a point where there aren't enough fibers to put a sheer force on the wood. The few intact fibers would have to split the wood across the area of cut fibers, which would be impossible in almost every possible scenario. So the box cut uses the same principle, just taking out far fewer fibers so it's best used when the chances of BBC are small. In the above scenario, it worked well because I didn't need to see what was going on.. it was fast and reliable