Hey guys!
I was the one who built the backhoe mounted stump grinder for my Magnatrac crawler. I ordered the hyd motor and cutter wheel from Power Trac made for their PT425 machine since my Magnatrac has similar hydraulic flow (about 8 to 10 gpm). After grinding a few stumps about 1 ft diameter with pretty good results I decided to go after the big Kahuna... a three trunk oak stump about 4 ft diameter. Grinding this was like grinding ROCK /forums/images/graemlins/ooo.gif I got about 1/3 way through and the hydraulic motor started leaking bad and smoking. It was toast /forums/images/graemlins/mad.gif
Power Trac sent me another (a White series RS - 460 RPM, 10 gpm flow instead of the Danfoss). I never got to find out what exactly failed inside it, but I believe that the direct cutter wheel connection to the motor shaft imparted end loads that the motor just couldn't hack. I haven't put the machine back together with the White motor which looks a bit beefier than the Danfoss, but I want to reconfigure the whole attachment anyway. Things I am going to change:
mount the cutter wheel on its own shaft with its own bearings so there won't be any excessive loads on the motor shaft
I envision having a sprocket and chain drive from the motor.
reorient the cutter wheel bracket so that when I go into stump with bucket curl the cutter wheel will be at an angle instead of straight (I'm going to make this adjustable to try different angles). Most stump grinders cut with the wheel side not the edge. This will allow scoop cuts instead of narrow slot cuts. It will also throw the chips to the side and away from the tractor /forums/images/graemlins/smile.gif
Making a 3 Pt version would be a bit more involved since you will have to add hydraulic cylinders to control the motion of the cutter. The backhoe already gave me up/down, side to side, and in/out controls so all I had to do was build a bracket to mount on in place of the bucket and plumb in the motor hydraulics. Buying the cutter wheel from PT also saved me from having fab it myself - reinventing the wheel so to speak /forums/images/graemlins/wink.gif Look at the various stump grinder manufacturers and you might be able to do the same.
Another way I've thought about mounting the grinder is on the loader with a bracket on a quick attach plate. Loader would give you up/down and curl, so all you would have to add is hydraulics to make the cutter go side to side. This would probably be simpler to fab than a 3 PT mounted machine.
Sorry for the long message. I hope some of this info gives you some help/ideas. If you got any other questions, just ask.
John
