The PTO, operated at 540 RPM, drives a heavy steel 24" diameter flywheel. Mounted on the flywheel are 34 tungsten carbide cutting teeth, as seen in the above photo. Once up to speed, the tractor is backed over the stump (with the grinder raised). Once in position, the grinder is lowered and the tractor slowly driven forward, allowing the teeth to cut through the stump. This is repeated as much as many times as necessary until the stump is at the desired height. The grinder is designed to remove the stump up to 6" below ground level. The stump grinder as a hinge assembly that allows the flywheel to pivot towards the rear should the tractor be moving to fast or to large of a slice is being attempted on the stump. If you see the flywheel pivoting rearward, you should stop forward movement to let the grinder "catch up". You will need to proceed at a slower pace or raise the hitch a bit to take less of a bite of the stump to prevent this from happening again.
Here is a pic of the WG24 stump grinder mounted on the three point hitch of my tractor. This was taken during the first trip into the woods to see how well it removed stumps. I tried it on a few poplar and oak stumps. It did a very good job.
The Woodland Mills website states the tractor used on the grinder should be rated at 20 - 45 HP. They don't say if that is PTO horsepower or engine horsepower. My Massey is rated at 28+ HP for the engine and 23 HP for the PTO. Regardless of which rating is being used, I would not want to use the stump grinder on a tractor with less HP than what I have now. If it were being used only on softwood stumps, you could get away with a little less HP, but not if you were going to be grinding hardwoods. When I was on the oak stumps, I had to take less of a bite compared to grinding the poplar stumps.
Before I ground this stump, I backed the tractor over the stump and lowered the grinder into position to take the first pass before I hopped off the tractor to take this pic. You can see clearly see the tungsten carbide teeth protruding from the flywheel. When I ordered the stump grinder, I also bought a 6 pack of replacement teeth, just in case I managed to find a rock or three out there in the woods. I suppose my next challenge would be to find someone that can sharpen these things. I'll have to check into that and if I find some helpful information, I'll update this write-up with it.
One of the stumps I took down to ground level during the inagural run of the stump grinder. That is easily low enough for the brush hog to slide over without contacting it.
Here is another stump that was part of the group I tackled my first time out with the stump grinder. I have hydrostatic drive on my tractor. The PTO runs completely independently of the transmission. And since it is hydrostatic drive, tractor speed is infinitely controllable which is perfect for operating the stump grinder. Prior to buying this one, I'd never used a hydrostatic drive tractor. I was a little hesitant at first but it didn't take long after buying it for me to realize I was liking it. Little did I know then I would be using it on a stump grind a couple of years later. It was a good decision.
Not all stumps I tried on that first trip to the woods were "perfect candidates". In this case, the tree was cut high leaving a stump that was too tall for me to back over even with the stump grinder raised to max height. It took very little time to slice a 6" thick piece off the stump with the chainsaw. After I did, it was just as easy to grind as the other stumps.
While I've only had about an hour of "stump time" as I write this, I can say that the learning curve was easy enough and the tractor and grinder worked well together. I'll say again that the hydrostatic drive makes it easy. I can imagine that after spending multiple hours looking over your shoulder at the grinder, one might be in for a good neck ache. Maybe the trick will be to alternate the shoulder you look over as you move from one stump to the next.
Here is a video I shot of the first stump I ground. I did it from the tractor seat so please understand I was filling the position of camera man and operator at the same time.
Update: Since writing the above comments a week or so ago, I took out another 18 stumps one afternoon. It did a good job. I think I'm going to put together a portable video camera and monitor setup for the tractor. Looking over my shoulder for several hours got really old, really quick (well, in about an hour anyway). Can you say neck and or back ache?
Update: I managed to put a high-quality video system on my tractor for use with the stump grinder. Wow! What a difference that makes. You can browse the review and install details of my camera and monitor system on my tractor.
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