I converted my stump grinder to a 2" square mount so I could use it horizontally. That lets me approach the stumps from different angles. I've cut down a few saplings, but it was painfully slow. If I were going to use it for brush clearing, I would definitely adapt a circular saw blade.
I also think a heavy duty circular saw blade might be best although I wonder how much flexing the blade might do as the tractor is moving side to side or forward to backward unevenly. If possible I would want to bolt the blade directly to the stump grinder's tooth mounting plate rather than adapt it somehow to the hydraulic motor shaft. The tooth mounting plate diameter is 14". To cut a 4" tree we would need a 22" or larger blade.
I spent the better part of today chasing down large blades on Craigslist and Ebay. I found several possibilities, usually older ones from primitive "buzz saws". One seller noted the blade was rated for 2200rpm. The teeth were aggressive and that is noticeably slower than most saw blades which would be in my favor. However I don't know how difficult it would be to drill holes in a saw blade accurately enough to keep everything balanced and true.
I also tried to locate a heavy duty pillow block, mandrel, arbor setup heavy enough to belt drive a large blade and I could not find anything worth working with.
What I did find is some useful info from this web site.
Turbo Saw - Tree and Brush Cutter for Skid Steer. This blade turns at 2000rpm at 10 gpm minimum. The shape of the blades could be duplicated on a smaller scale and bolted to the stump grinding teeth mounting plate. My brother suggested trying high speed rotary hay mower blades on it. If they were 1/4" thickness they might be heavy enough.
They also have a tractor model at
Turbo Saw - Tree and Brush Cutters for Tractors.
To quote them "This model runs a high speed circular disc with durable carbide cutting teeth, the Turbo Saw TR3200 can operate on tractors with 28 - 120hp. On a 540 rpm PTO the disc turns at 1000 rpm cutting up to 8" per second. The mining grade carbide teeth can contact the ground to insure a smooth ground level stump."
I would be happy to be cutting at 4" per second! Actually I'd be quite happy cutting 1" per second! It looks to me like this may be doable!
I'm going to mentally process this a bit more but right now I think this is the direction I want to go. My brother has access to a plasma cutter to cut out the blades and I have a heavy duty drill press for precise drilling of the holes. When finished we can harden the blades by heating and water quenching.
Any and all thoughts on this would be deeply appreciated!