Safe Use of Stump Grinders

Richard L. Parish, PhD, PE

Large stump grinders that are pulled behind trucks are used by many professionals for stump removal. Those machines can grind a stump very quickly and efficiently, and may be safe if used correctly and carefully. There are also several models of small, less expensive walk-behind stump grinders that are aimed at homeowners, rental use, and smaller professional operations. Some of those small stump grinders are reasonably safe if used carefully, but a few are not safe no matter how they are used.

Types of Small Stump Grinders: Most small walk-behind stump grinders have an elongated frame with wheels and an engine near the center, a handle for the operator at one end, and a cutting wheel at the other end. The cutting wheel can be mounted in a horizontal or vertical orientation, but vertical is more common. The cutting wheel is usually belt-driven from the engine. A typical cutting wheel is comprised of a heavy wheel with replaceable tungsten carbide teeth that do the actual work. The cutting wheel does not "saw" the stump, it "grinds" the stump. A sharp cutting wheel will reduce a stump to chips.

How a Stump Grinder Is Used: Most stump grinders are designed to be operated in a back-and-forth mode. Moving the handle left to right moves the cutting wheel right to left. As you move the handle back and forth, the cutting wheel will move back and forth across the stump, gradually grinding it town. After each pass across the stump, you either lower the cutting wheel (by raising the handle) or move the whole machine forward an inch or so. Some machines have a brake on one wheel so that the machine can more easily be pivoted about that wheel.

Unsafe Designs: Some stump grinders, especially some obsolete models that may still be in service, have the cutting wheel on the same end of the machine as the operator. In this case, the cutting wheel is essentially under the handle. The manufacturers of this type claim better visibility of the cutting wheel, but this design is extremely dangerous and should never be used. There have been dozens of very serious injuries from this type of stump grinder. Not only is the cutting wheel too close to the operators legs and feet, but the wheel rotates backward, thus if the teeth grab, the machine will jump back at the operator. In testing one of these machines (using a remote handle), I have had a 300+ pound machine literally jump off the ground and leap back at where the operator would normally have been standing.

Safety Considerations in Use: Obviously the first consideration is to use only stump grinders with the cutting wheel on the end opposite the operator. A further consideration is that you should not use a small walk-behind stump grinder unless you are physically fit and reasonably strong - you will have to wrestle it around. Don’t use a stump grinder unless you have been properly trained in its safe use. Keep all bystanders - especially children - far away from the machine. A stump grinder with the blade opposite the operator won’t kick back at you, but might jump forward and injure a bystander. Not only is the cutting wheel dangerous, but the machine can throw objects a long ways. Watch out for rocks, buried pipes and electric wires, concrete, etc. Don’t try to take a deep cut; don’t force the machine - let it feed itself. It is very important that you keep the teeth on the cutting wheel sharp; sharp teeth are less likely to grab and jump. It is important that the machine have an operator presence control to stop the cutting wheel if the operator leaves the operating position. On most machines, you should shut off the engine before moving the machine. Most machines use centrifugal clutches, which are notoriously unreliable, so you can’t count on the clutch to keep the blade from turning when you move the machine. Don’t leave the operator’s position behind the machine when the engine is running.

Small stump grinders are very handy tools, but are too specialized and too expensive for most homeowners to own. Your most practical choices are to rent a stump grinder or hire a professional. If you decide to rent a machine and do the job yourself, be very careful. Stump grinders are powerful machines that can chew up feet and legs as easily as they chew up stumps. Always treat a stump grinder with respect and never become complacent while using one.