Piston and Nealfris:
I mounted a Bush Hog brand 48 squealer rotary mower on a FEL and drove it with the kind of PTO pump JJ recommends. I spent a bit more than he estimated for my reservoir, but otherwise he is right on. You can稚 do it for less than his $1,000 estimate and you could easily spend $1,300 or so with filters, relief valves, etc.
If it were me I would give it a try using your tractor hydraulics. You are going to install the remotes anyway, so the additional cost to give it a try will be a $250 hydraulic motor, $50 motor mount, $100 for pulleys and belt, and $100 for hoses and fittings. If it works you can add a separate motor valve to make starting and stopping easier, check valve to let the motor overrun the pump, and other refinements.
I think it might work. Say your hydraulic system pressure is 2250 psi. 6.9 gpm produces almost 9 horsepower. Even an 80% efficient motor will produce 7 hp at the shaft. There are lots of push type 21 rotary mowers that cut lawns and weeds just fine with a 4.5hp rated gasoline engine that is undoubtedly overrated. Your deck was driven with 10 hp, probably overrated, that also drove the wheels and carried a passenger. So 7 true hp should turn a 28 blade in grass and light brush..
It might not be able to keep up in heavy grass or weeds if it is being pushed fast, but you are not likely to do continuous cutting with the mower deck on a backhoe. If there is a continuous cut at all it will be very slow because you have to follow the contour of the ground with the boom and dipper stick. Most of us don稚 use the backhoe regularly enough to maintain the kind of skill to move the end of the stick very fast with that kind of precision. It will be much more put it down, let it cut, lift it, and put it down a couple of feet over. The blade should have plenty of time to recover speed while you are moving it over the grass.
I agree with JJ about blade speed for finish cuts on a lawn, but I assume you are not seeking a golf course cut. My Squealer with 48 cut has a blade tip speed of 13,000 feet per minute (4 x 3.14 x 540 x 1.92) and it cuts pasture grass and brush fine even when the blades are dull. And those blades are 3/8 thick. Blade sharpness obviously is important, but blade thickness also matters more than I would have thought. I have a 5 Bushhog with ｽ thick blades that takes quite a bit more power per foot in heavy grass than the Squealer with its 3/8 blades, and blade thickness seems to be the main difference.
Your 28 blade is probably ｼ thick and, with it so accessible you should have no problem keeping it sharp. It is only an educated guess, but I believe 7 true hp will spin a sharp ｼ thick 28 blade quite well in heavy grass, weeds, and brush under 1 diameter.
I would aim for a blade speed of say 15,000 fpm for another reason as well. You will not be able to shroud the blade fully and it will be tossing sticks and stones back your way. The slower the blade speed the slower those missiles will zing by your head; I know this from experience.
A 28 blade turning 2,000 rpm gives about 15,000 fpm at the blade tip. A 2 cu in motor will turn about 800 rpm, so a 2.5 step up from the motor pulley to the spindle pulley will produce 15,000 fpm.
If it turns out that your hydraulic system does not have the capacity, you can add a 15-20gpm pto pump and change the pulley sizes to keep the spindle at about 2000 rpm.
I think the biggest problem with using the tractor system would be hydraulic fluid temperature if you keep the mower in heavy cutting constantly, but you are not likely to do that.
Sounds like a neat project. Send pictures.
