If I'm felling for firewood in a dangerous area like by power lines and or roads, I'll use the Open Face at 90 to 110 degrees depending on how high I make the stump by where the ground level the tree will end up is. The larger the difference in elevation the wider the Open Faced cut. This is when I need control all the way to the ground. Using the Conventional face cut, I'll use this cut for basic tree removal. Using the Humboldt face cut, I'll use this for a tree that will end up being lumber as there is less waste going as close to the ground as possible. Bore cuts are for when a delay might be needed to check the surrounding area for traffic or people. I also use them for when there is a risk of a sit back where the tree could sit back on itself and make sure wedges are in place. This includes for back leaners. I'll also use the bore cut for forward leaners and rotted trees. How I end the cut is dependent on the situation. This will also help in the prevention of a barber chair. Back cuts for the conventional and Humboldt are placed an inch to no more than two inches above the face cuts ending point. This prevents the tree from jumping or slipping back off the stump. For open faced I'll usually go level with the ending point of the face cut or a little above, but usually no more than an inch. My stumps can end up being 34" to 2 inches in height. For the open faced 34", I'll end up cutting it further leaving 2 inches above ground level. Then cut the remaining 32 inches in half for two 16" rounds. (firewood) For the Conventional and Humboldt, the stumps I leave are anywhere from two to four inches in height. Beware the Dutchman! That is where either of the two face cuts extend further than where either connect. This can cause premature breaking of the hinge causing the tree to fall in a different direction all together. As for the hinge, I won't go into that here because there are many variables when it comes to directional felling especially when your dealing with felling back, side and forward leaners (or any variable like leaning to the side and back) As with any tree felling, if your not comfortable with the situation or the tree where it might prove to be too dangerous, call in a professional or tree service. It's not worth the risk getting hurt.
I tell over 45 degrees , even with a 45 degrees the trees fall without any problem , i cut about 2500 cubic meters every year and i have see all theese situations