An OC Guide to the Stump Grinder

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Trees in the yard can age and die, or become diseased due to tree infections, or dry due to girdling. Such trees need to be cut and felled.

Also, healthy trees can be felled during landscaping, tree care of forests, or when freeing up yard space for other uses.

One can pay for professional tree removal services, or cut down the tree using a chainsaw. Also, during yard beautification, the landscaper can offer this tree removal service.

Even so, when removing the tree, it is rare for the tree to be uprooted entirely with its roots. Usually, the lowest part of the tree trunk that extends from the roots remains, and this portion of the trunk is the tree stump.

If coppicing is not desired, then the tree stump and its roots need to be removed completely, and this process is called stump removal.

A related process of removing the stump is called stump harvesting, and it involves using a specially tracked excavator, or stump puller, to pull out (or simply uproot) the stump from the ground so that its wood can be used as fuel in biomass power stations.

Stump removal can be done in 5 ways; burning the stump, digging it out (the technique used for stump harvesting), chemical stump removal (using [potassium nitrate] KNO3-based chemicals that accelerate stump decay), blasting stumps (using explosive stump powder), or shredding it into chips.

The equipment used to shred, or chip, the stump is called a stump grinder (SG)

Stump Grinder (SG)

Stump-grinder

This is a mechanical device that uses engine power to drive a bladed cutting disc/wheel at a high (rotational) speed so that it can slice and dice a tree stump along with its roots (below surface level) into woodchips and sawdust, which can then be used as fuel or mulch.

This leaves a stump-free ground that can be flattened using the sawdust, woodchips, and dirt, which fill the hole left by the chipped roots.

Basically, it is a piece of power equipment used in stump and root removal. As expected, it combines the function of a stump remover and root grinder into a single outdoor equipment.

This equipment is usually designed for use by professional arborists, or anyone engaged in arborist stump grinding.

As expected, the user of any SG (otherwise described as the machine operator in SG manuals) must follow the instructions laid down about how to use the SG. This allows the operator to get the most out of any SG.

One can also use an SG to remove a stump confined in a tight space because of backyard hardscaping with concrete walls or buildings.

The functional design of an SG combines the functions of a grinder and wood chipper into a single cutting component called the cutter head.

The principal component in the cutter head is a toothed cutting disc known as a cutter wheel. Like the fuel-powered woodchipper, the stump grinder is usually powered by an internal combustion engine, which runs the cutter wheel.

This cutter wheel spins at high speeds which allow its carbide teeth to chip the stump and its roots. As expected, the cutter wheel must be pushed into the ground when obliterating the tree roots.

To achieve this, a hydraulic mechanism is used to push the extension arms that hold the cutting head. It is the forward pressure exerted on the extension arm by the hydraulics that pushes the cutting wheel into the stump.

This hydraulic mechanism is operated by hydraulic cylinders that allow the user to lower or raise the cutter wheel.

Even so, some SGs do not use a cutter wheel, and the most prominent atypical SG is the vertical SG.

Vertical Stump Grinder

This is a special SG that uses a bladed drill to grind a tree stump. As expected, the drill must be pushed into, or pulled out of, the ground, hence the designation vertical SG (VSG).

VSG is usually used to destroy tree stumps whose diameter exceeds 1.5meters (1.5m) and have arborized roots that have grown more than 1m deep into the ground.

Even so, this review focuses on standard SG, and one should use the right type of SG to complete the existing task.

Workload Determinants

The 4 variables that determine the workload for an SG are stump size, stumpage, the hardness of stumps, and the number of stumps that need to be removed.

Also, if the stump is located in a tight space, (then) there is a need to ensure that the grinder can reach it (stump) and still have enough space that allows the user to sweep the grinder side-by-side when chipping the stump.

Stump Age

tree stump

If the stump is what remains from an old felled tree, then one expects it to be harder than a stump from a younger tree of the same species.

There are age-defining rings of the tree that can be seen clearly on the stump and using dendrochronological knowledge, one can estimate how old the tree is.

Dendrochronology is the study of age-defining rings of tree trunks. As a rule of the thumb, the older the tree, the harder the stump and the deeper and more arborized the roots; or in other words, the older the tree, the more work is needed during stump removal.

Another consideration about stumpage is how long has the stump existed after the tree was felled and whether the stump has started to rot or not.

As a rule of the thumb, the longer the stump stays, the more it rots; and the more rotten is the stump, the softer it becomes (as compared to a freshly-cut stump).

Hardness of Stump

This is based on the wood quality and species of the tree from which the stump is derived from. As expected, a stump from hardwood species is harder than stumps from softwood species.
Also, as mentioned earlier, a freshly-cut stump is harder than a rotten stump.

Stump Size

tree stump

There are two considerations about stump size: stump diameter and stump height.

If the stump is 12inches tall (above ground level), then any SG can be used; but if it taller than 12 inches, then only a tracked or wheeled SG can be used.

Else, one needs to cut it to reduce its height to 12inches or less for the handlebar SG to be used.

Even so, if the stump is taller than 35 inches, then one must cut it down to a lower height as the tracked SG – whose cutting head is fitted to a separate boom – can only raise the grinder to a height of 35inches.

Stump diameter determines how large the stump is, as well as allows the operator to estimate how large the root base is. If the right cutter wheel has been chosen, then the stump diameter can determine how quickly the task will be completed.

Usually, one can gauge the suitability of a blade of a particular size to chip the stump by comparing the blade diameter to the stump diameter.

If the blade has a larger – or equal – diameter to the stump, then it can easily and quickly chip the stump.

Number of Stumps

This is self-explanatory as the more the stumps in the yard or field, the more work there is.

Usually, a high number of stumps in a single yard requires one to use a self-propelled SG because it is highly mobile and can easily navigate the yard.

SG Operations

Reluskie / Public domain

As mentioned earlier, the SG grinds and chips the tree stump and its roots. Its basic operation involves 2 sequential steps:

Rotating cutter wheel – This is the first step, and it involves engaged of the cutter wheel to the power transmission system, which allows the wheel to spin.

It is this spinning cutting disc that is pushed into the stump and in the process slices it.

Sweep – Usually, the cutter wheel is just pushed about an inch into the stump and this allows it to slice a portion of the stump, and to remove this sliced portion, the spinning cutting disc is moved laterally (side-to-side) which causes it to pulverize the stump.

These lateral movements of the cutter wheel are called sweeps, and they allow the wheel to chip the stump.

As a precaution, the operator must never adjust handle height and position of a handlebar SG while the SG is running.

Regarding sweeps, the locking brake allows the operator to pivot the SG. The locking brake usually locks one wheel (usually the right wheel), which allows the operator to move the other wheel to create sweeping grinder movements that enable the grinder to chip the stump.

Basic Components

There are 3 basic components in an SG:

Cutter Head:

The cutter head houses and holds the cutter wheel. Usually, this wheel is covered on its top part by a cutter wheel guard. The sides of the (cutter) head are extended (to touch the ground) by chip curtains which ensure that woodchips are not thrown far from the Jobsite. Some models feature a safety shroud instead of the wheel guard.

Power Unit:

It provides power to the grinding wheel. This power is generated in four-stroke internal combustion (IC) engine that burns diesel or gasoline/petrol. Power is transmitted from the engine to the cutting disc through a geared linkage, belt drive, or a power take-off shaft.

Control Unit:

This allows for the operation of the SG machine, and it determines whether the machine is operated manually, or if its operations are automated to run from a control panel.

This unit controls maneuverability of the SG, and rotations and lateral sweeps of the grinding wheel. It takes advantage of the articulated nature of tool bars and beams – which connect the cutter head to the hydraulic-operated extension bars – to operate the machine.

Types of Grinders

There are 5 types of SGs, and they are explained below.

Handlebar Stump Grinder

This is an operator-friendly SG that allows one to use the handlebar to move the cutter wheel forward or backward. To make the sweep, this SG must pivot on one locked wheel while the other mobile wheel is pushed forward or pulled back.

The width of most entry-level handlebar SG is less than 34 inches which makes them compact and suitable for chipping stump in tight spaces.

Handlebar SGs are lighter and easier to transport as compared to tracked SGs. Moreover, one needs to have a trailing unit so as to move about the tracked SG.

Tracked Stump Grinder

This is another operator-friendly SG that uses tracks for mobility, and controls are provided to adjust movements of the cutter wheel and allow for sweep action.

Also, the operator can adjust the sweep speed. As expected, this tracked SG completes tasks much quicker than the handlebar SG because its operations are automated, while handle SG can best be described as manually-operated equipment.

It is usually a self-propelled SG that uses rubber tracks. Self-propelled in this context means that the operator can climb onto a seat and drive the SG around the yard. This means that this SG is a special-purpose vehicle for grinding tree stumps.

A high-quality tracked SG can automatically slow down its sweep speed if it encounters a resistant load, that is, if it is forced to grind through exceptional hardwood which puts a lot of resistance on the rotating cutter wheel

Most tracked SG has a width of 34 inches or more. Moreover, their tracks are designed to evenly distribute the equipment’s weight on the ground which reduces the pressure the tracks exert on the ground surface.

This allows the operator to use the SG without leaving (or only creating very faint) ruts and turn marks on the yard.

Even so, there are some tracked SGs that are not self-propelled and these are usually medium-duty to light-duty models that require their operators to push them around, and they are called tracked walk-behind stump grinders.

Self-propelled Wheeled Stump Grinder

This is basically a tracked stump grinder whose tracks have been replaced by 4 wheels, which converts it into a special-purpose automobile (SG). Some models are 4-wheel drives.

PTO attachment Stump Grinder

Some SGs come without an engine, but feature splined power take-off (PTO) drivelines of specific lengths.

This PTO driveline can be mated to the drive shaft of a tractor or any other engine. This type of SG is usually suitable for people who infrequently engage in stump removal.

As expected, due to the straight and solid nature of the PTO shaft, it is difficult to use this SG in tight spaces.

Nonetheless, this problem can be solved by using an articulated PTO shaft, but this shaft is quite expensive and its installation requires one to be experienced.

Tow-behind Stump Grinder

This is a large, heavy-duty wheeled or tracked SG that comes with a large cutting disc, and needs to be towed by a heavy vehicle such as a tractor. Its operations are automated.

Safety

Using an SG poses a safety risk if it is used improperly, or the user is improperly outfitted when using it.

Here are some of the basic safety precautions and guidelines:

SG throw chips during operation and it is important for the operator to confirm that there is no person around the work area and that windows and doors are shut if stump grinding is done next to a house, school, or office blocks.

  • Wear protective clothing.
  • If using the handlebar SG, do not exert too much downward force of the cutting head so as to slice deeper into the stump as this can increases its workload beyond its handling capacity.
  • Exercise manufacturer-stipulated care when operating a tracked walk-behind SG in an uphill or downhill jobsite on sloped ground.