In theory, as long as the engine or PTO RPM's aren't dropping, I shouldn't tear anything up. If I back in slowly and let the momentum of the blades spinning on the 3/4" plate do the work it should be fine. I'm not planning on tackling a 12" pine tree with this. I want to build this to be able to take down trees greater than the 1.5" that my current brush deck allows. I think anything less than 6" should be easily cut and mulched.
The deck I'm going to use is an ancient Brush Hog deck.
Please talk me out of this if it's a terribly stupid idea. It certainly won't be the first time.
I built one for my ASV RC30, took an old 4' bush hog that the deck was rusted out on, pulled the gearbox and blades. Ditched the frame and PTO shaft. Used a plate made of 1/4" steel for the deck, and reinforced with some 3/4" steel, behind the gearbox. (used the original gearbox mount from the old mower) Then put a hyd motor in place of the drive shaft, and made a mount for it, and welded the mount to the 3/4" steel. Braced it with heavy 2X3 tubular box steel, for the quick attach plate, and some 1/4" angle iron along the front edge. Has about 6" sides with skid plates along their full length.
In retrospect, I wish I had checked out the stump jumper off the old mower, cause the holes were wore out on it, so I had to replace that, for about $125, if I remember the price right. It is heavy enough that I can push down 3-4" trees, and chop them on the way down. Much bigger than that and it's easier to just cut the trees with a saw, down low, when you come to them.