View Full Version : Stumpy: Mark III

06-25-2011, 09:05 PM
I will be doing some more logging this summer up and around the house to improve the view for my telescope and reduce fire hazard. That means a lot of stumps to clean up. My previous stump grinder that I built from a rototiller works just fine but it isn't up to the task this time.

So, I built a new one, much more capable with a lot more power. I used a 15 hp Briggs from a spare lawn tractor and a very heavy cast iron roller from a small mining conveyor. The roller was given to me by a friend from his scrap pile and is mounted on very sturdy pillow blocks with self aligning ball bearings. The drum is around 100 lbs by itself so it has a great amount of angular momentum when it is spinning at 1000 rpm. It is fitted with three rows of tungsten carbide Rhino Teeth used on gang saws. They can cut through spikes with no trouble at all. There are around ten teeth per row.

I had to make the belt drive turn 90 degrees since the engine is a vertical shaft. I also had to build a suitable pulley for the drum to fit the two inch shaft. That put my new drive belt on my South Bend to the test and it handled it very well. The SB can now take ~0.1 DOC with chips that go clink when they hit the floor.

The new grinder does the job really well and it doesn't take long even on good sized stumps. It much easier and faster than the hand operated earlier version. It's all electro/hydraulic controlled from the cab of the Rover and can be angled as well a raised and lowered with precision. It will spit out chips 30 feet ahead when it takes a good bite.

I still have a few details to take care of such as mounting the engine controls and wiring up a kill switch in the cab. The unit weighs around 250 lbs but is very easy to remove as it is held on the lift frame by just a single pin.

I also need to make a more permanent belt tensioner arrangement.




This stump was around 5 inches high and took maybe 20 minutes to grind to ground level. It probably could have been done faster but I was having belt problems. I have that sorted out now. The spacing of the idler pulleys is pretty critical to prevent the belt from climbing off.


06-25-2011, 09:06 PM
Here is a closer look at the drum and teeth.


06-25-2011, 09:54 PM
Is there anyway you are transferring anywhere near full HP? I'd think one belt would never pull that off, or is that a safety mechanism?

06-25-2011, 10:06 PM
I am sure it isn't transferring full power but there isn't any easy way to use two belts.

06-25-2011, 10:14 PM
Very interesting set up.

Yes i wondered also about the one belt at least it looks like it could slip?

Thanks for the neat pics!!!

06-25-2011, 10:31 PM
The belt will slip but there is a heck of a lot of energy stored in that spinning drum. I back up to take another bite and the drum comes up to speed. I make a good pass over the stump using up that stored energy and I take another pass. So, on average it is transferring more power intermittently than the belt can handle continuously. It's easy to tell when it is back up to speed in just a few seconds because the motor stops working as hard. On the original lawn tractor they use just one belt to drive the tractor and another to drive the blades. With the blades disengaged it is single belt drive.

06-25-2011, 10:44 PM
Way back in '72, we worked with some people who had a sugar daddy wanting to build a super mulcher for use in clearing pipeline rights of way through LousieAnna, East Texus Big Thicket, etc. Machine was built on a D9 Cat using a V8 Detroit Diesel mounted cross saddle behind the operator, driving the front mounted chew roll via a nest of large v belts. Good operator could fell a large pine and mulch it in one pass, but had trouble being too agressive and causing the v belts to throwup. Good operator could fell a pine and make it fall outside the right of way, out of bounds. Machines went to Arizona to clear a right of way, never to be heard from again. Trees and rocks and minimal moisture unlike the Gulf Coast caused bankrupcy.

Todays version of the same machine and service:





06-25-2011, 10:47 PM
You could always go with a hydraulic pump and motor to drive it.

Wouldnt it be better to stagger the teeth in a helix around the drum to smooth out the vibrations?

06-25-2011, 10:56 PM
I would have to buy a hydraulic pump and motor. I didn't have to buy anything to build this. I thought of staggering the teeth but it is a lot more work and uses a lot more gas to braze them. In a row the spot for the next tooth is already nearly up to temp from brazing the one beside it. As it is it takes a good while to get it up to temp. That drum is at least a half inch thick except at the edges. In the centre it is solid for the middle third.

06-26-2011, 03:25 AM
I wish I had some pictures of the monster stump eater I built in the mid-'80s.

It had the engine and transmission out of a Chevette driving a 30" diameter cutting wheel made from three pieces of 3/8" steel plate welded together. Final drive to the cutter wheel was by a spring-loaded boat trailer tire against the side of the wheel just inboard of the cutter mounts.

The drive train and wheel were mounted on a frame that rocked on trunions mounted on a sub-frame that included the tongue. A trailer tongue jack controlled the depth of cut by raising the front of the cradle. The sub-frame itself could be cranked side to side across the axle, and the tongue could be extended and retracted with a third hand crank. It would cut a 24" diameter stump flush to the ground without moving the truck.

The stump eater worked pretty well, but all the hand-cranking made it very tiring to use.

This was all accomplished without a lathe and mill. All I had was a OA torch, a buzzbox welder, a grinder, a 1/2" drillpress, and some assorted hand tools.

The whole project started as an office bet that I could built a working stumpeater for less than $600. Getting the complete Chevette with a busted cam for $100 made it easy to come in under budget, especially after I sold the gutted body for $50. :D

06-26-2011, 04:34 AM
That's a handy tool. Do the stumps just die after being milled down below ground level or do they keep popping out of the ground and need cutting down again?

06-26-2011, 09:27 AM
reminds me of a Corvair.
Corvair idlers were two V belt pulleys.
They would occaisionally throw belts as well.

Way, way off topic.

Anybody know what happened to the Corvair junkyard just outside of Madison Wisconsin on US 14?

06-26-2011, 10:47 AM
Do the stumps just die after being milled down below ground level or do they keep popping out of the ground and need cutting down again?

With conifers once it has been cut below the lowest living branch the tree dies. The stump will rot eventually.