An OC Guide to Wood Chipping Machines
On the farm, unwanted tree trunks, logs, and large tree branches are unsightly, take up space, and create a potential hazard that can cause people to trip and fall down.
Even so, such unwanted wood need not be burnt or thrown away, but can instead be broken down into small wood chips to be used to line flowerbeds, surface the ground, pave a walkway, or serve as fuel for barbecuing, or even create compost to be used as fertilizer or mulch.
Even so, how does one get wood chips from large chunks of wood?
The answer is that this is done using a piece of specialized woodworking equipment called a wood chipper.
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The Wood Chipper
A chipper is any piece of equipment that can shred large masses of material into smaller bits. As expected, the basic meaning of a wood chipper is a piece of woodworking equipment that breaks down trees, branches, and twigs into small bits called woodchips.
These woodchips range in size from 3 inches to less than 0.5 centimeters (cm) long. It is also expected that energy must be used to operate the woodchipper, and this energy is usually provided by either electricity or burning fossil fuels.
Therefore, the most appropriate definition of a woodchipper is that it is powered woodworking equipment that cuts large chunks of wood into small woodchips.
This equipment is also called a tree shredder or tree chipper if it is designed to cut tree trunks into woodchips.
It was invented in 1884 in Germany and its construction and operational design have undergone significant changes to improve its work efficiency and output.
The two main considerations that determine the functional utility of any woodchipper model are the size of wood it can cut down, and how small the woodchips it produces are.
This is important because woodchip size determines its usage, with large chips of 3inches being suitable for making wood pulp, or as a solid fuel for barbecuing, space heating, and heating industrial boilers.
Small chips of 0.5cm or less are used as mulch or are reprocessed to be used as a playground surfacing material to make an impact-attenuation cushion that can safely break a fall from a height of up to 3 meters.
Likewise, woodchips (both large and small) can be piled in waterways dug in fields where they act as bioreactors that employ heterotrophic denitrification to break down nitrates, hence reducing nitrate pollution of water downstream.
Likewise, woodchips can just be scattered in the yard. Landscapers can also use woodchips for yardwork and yard beautification.
Evidently, the size of woods that one needs to cut and the subsequent use of woodchips are the key determinants of which woodchipper one needs to have.
As mentioned earlier, a woodchipper can be used to reduce yard debris, including pruning debris and fallen branches, into small woodchips that can be used as mulch or for layering the yard.
It is therefore useful in places where legal restriction prohibits landowners from burning debris in open fields or placing their lawn trash on curbsides for pickup.
After understanding what a woodchipper is, and its basic functions; there is a need to describe its basic components.
Components of a Woodchipper
The woodchipper has four basic parts: the inlet which delivers the wood to the chipping unit that is run by an engine that powers its chipping mechanism when breaking down wood into woodchips that are then spat out of the chipping unit through an outlet.
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This is the inlet port that allows the user to feed wood into the machine. In small- to medium-sized models, this inlet is usually a hopper with a collar, or a collared inlet chute (also called entry or supply chute).
The size of the inlet port at the point where the inlet feed meets the chipping unit determines the thickness of wood that can be pushed through the inlet feed into the chipping mechanism.
The feed capacity is the maximum wood thickness that can go through the inlet into the chipping unit. Usually, the size of the inlet chute and blade sizes in the chipping mechanism determines the maximum thickness of wood that can be feed into the woodchipper.
In some models, a smaller secondary chute is used to feed small twigs and soft branches into the chipping unit.
Feeding tools, such as feeding sticks, are used to push the wood down towards the chipping unit.
In large woodchippers, a feed wheel that has horizontally-oriented serrated blades on its exterior surface is used to push wood and tree trunks into the chipping unit.
In other heavy-duty models, the inlet feed is a jagged conveyor tray with grooved rollers (which act as feed wheels) which carry wood into feed funnels where the wood enters their chipping units.
This holds the chipping mechanism that cuts down the wood into small pieces, and it is the heart of the woodchipper.
It is made up of 3 components:
- A casing which forms the chipping chamber;
- the blades that cut the wood;
- and the heavy rotating object called the impeller that holds the blades in place and spins at high speeds to gain kinetic energy and inertia that allows it to drive its attached blades forcefully through the wood.
The impeller with attached blades creates the chipper.
There are 3 types of chippers:
This is a drum oriented horizontally with blades attached to either its external or internal surfaces. Usually, the blades are placed horizontally on the outer surface of the drum.
Generally, at least 4 blades are attached to the drum.
This drum is driven by the engine, and it is set to rotate in a manner that spins the woodchips towards the outlet, and this also allows the drum blades to draw in (‘suck’) the wood from the inlet feed. This is called self-feeding.
This chipper can handle large hardwood chunks, but it needs lots of energy in order to attain sufficient kinetic energy to drive its blades through the wood.
Moreover, it produces large woodchips that vary in size from 3 inches to 1 inch. It is colloquially called chuck-and-duck chipper because it quickly draws in the wood through its self-feeding mechanism.
This is a flywheel disk that is oriented vertically and blades (also called flails) fitted on its chute-facing side (the side facing the inlet feed).
Usually, the blades are set diagonally at 45 degrees on the disc. This means that the inset blades are slanted at an angle of 45º to the flywheel surface, and this allows the blades to scrape wood and carry the scraped woodchips towards the outlet.
The blade base is bolted, riveted, or welded to the flywheel.
Compared to the drum chipper, this is a faster and more energy-efficient chipping unit that produces woodchips of nearly uniform sizes. Even so, most commercial models are suited for small tree branches.
This is a conical blade shaped like a screw, and it spins in a spiral motion that allows it to draw in wood from the inlet feed.
Basically, this screw blade is either a tapered and bladed screw conveyor, or a tapered blade that has been twisted through 360º or more.
It produces chips of uniform size, and to change the size of woodchips, one needs to change the screw blade itself. It is also called a high-torque roller and is usually driven by electric motors.
Compared to either the drum or disk chipper (which is usually driven by fuel-powered engines), this chipper is safer, quieter, and easier to use.
The blades used can have sharp cutting edges or semi-blunted edges. Some also come with sharp serrated cutting edges.
Apart from the screw blade, the other blades used in woodchippers are rectangular and are made from an alloy of high-grade steel (92%) and chromium (8%), or just high-grade steel whose cutting edge has been hardened by heat treatment.
The length of the blade ranges from 6-12 inches, and its width ranges from 1.5-4 inches.
The woodchips that exit the chipping unit to the outlet are usually less than 2 inches wide.
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The engine accelerates the drum or flywheel and allows either of them to attain sufficient kinetic inertia to drive blades through the wood.
As expected, the engine power determines the kinetic energy that the chipping unit attains. This engine needs to be connected to the chipping unit, and this is achieved using 2 means:
The drive belt is used alongside pulleys, and it can be a flat belt or a V-belt (ribbed or smooth). The chipping unit is fitted with a large pulley, and the engine crankshaft is connected to a small pulley.
The drive belt is then attached to these pulleys, and this allows for engine motion to be transferred to the chipping unit. Threading the drive belts improves the integrity of motion transfer.
The driveshaft can extend from flywheel (connected to the engine crankshaft) to the central axial shaft of the drum, disc, or screw-blade; or it can be an articulated power take-off (PTO) shaft that is part of a geared power transmission system.
Gears in the power transmission system allow for regulation of chipping speed in the chipping unit.
There are usually two types of engines used with woodchippers:
This is basically an AC (alternating current) motor. This motor produces enough power to drive the chipping units of wood shredders, chipper shredders, and small woodchippers.
Even so, it produces less torque as compared to fuel engines, and hence it can only be used by small woodchippers to shred and break down softwood, small branches, and twigs.
Even so, unlike diesel or gasoline engines, electric motors do not produce exhaust fumes. Electric motors are also cheaper and easier to maintain as compared to internal combustion engines.
However, these electric engines need to be plugged into an AC power source which limits the mobility of the woodchipper (unless one uses a long cable or a portable AC power supply unit).
Therefore, if one needs a truly portable woodchipper, then the model chosen should have an internal combustion engine.
Internal combustion (IC) engine
This can either be a diesel or gasoline (petrol) engine. The size of the engine determines its power output, and the basic fact is that the larger the engine, the more the power output.
Nonetheless, the types of fuels burnt also determine power output because of their different combustion properties, their distinct types of engines, and their distinct ignition systems used in these engines.
Most IC engines used to power woodchippers have a power rating of between 3 HorsePowers (HP) and 1000HP.
Also, heavy-duty, high-powered woodchippers with hydraulic cranes are run by special heavy-duty engines whose power rating can exceed 1000HP.
After the wood has been broken down into chips, these chips need to be expelled from the chipping unit and out of the machine through a discharge spout or chute.
In the chipping chamber, there are flanges inside the chamber, and/or fins located behind the impeller, that direct chipped wood towards the discharge chute or spout.
Additionally, the airflow and spitting action of the impeller causes the chips to be thrown towards the discharge spout at a high speed which allows for their exit through the spout opening onto the ground or truck-mounted container.
In some small- to medium-sized models, a collection bin or collection bag is fitted to the discharge spout to collect the woodchips. Usually, these models are wood shredders or chipper shredder which are explained below.
Woodchipper is the collective term for 3 closely-related machines: the wood chipper, wood shredder, and tree shredder.
The wood shredder is a small-sized woodchipper that has an inlet chute for feeding wood and debris into the chipping unit, which uses semi-blunt blades (flails) to cut the wood.
The user can choose the size of the woodchips that are to be released through a discharge spout. The use of semi-blunt flails and a small engine makes this equipment unsuitable for breaking down large branches and hardwood branches.
It is also cheaper than the standard woodchipper. Moreover, some wood shredders operate like powered wood whackers, while others use strong nylons instead of metal flails (though these are usually used for shredding small soft twigs, leaves, and soft organic matter).
This equipment is also called a mulch shredder or compost shredder.
Standard wood chipper
The standard wood chipper has an inlet chute that feeds wood to the chipping mechanism that uses sharp metal blades to break wood into wood chips measuring 1-3 inches in length and then spatting out these wood chips through a discharge spout into a collection bin, or onto the ground.
Its chipping unit can be a drum chipper, disc chipper, or screw chipper. This equipment can chip both freshly-cut wood and dry wood, and can also chip hardwood. In this review, this wood chipper is simply called a chipper.
Likewise, the woodchip will simply be described as the chip.
There is also equipment that combines wood shredder function into a wood chipper, and this machine is called a chipper shredder.
It is usually smaller than the chipper and the maximum thickness of the wood (or tree limbs) that can be fed into it is usually 3 inches, though some models come with detachable inlet chutes which allow the user to feed wood of different sizes to the machines.
Likewise, some models feature smaller secondary chutes for feeding wood debris to the shredder.
This equipment allows the user to choose the woodchip size, and most come with a screen attachment that ensures that chips of larger sizes do not exit the chipping unit, but are instead thrown back to the blades for further breakdown to the desired size.
This is the most suitable equipment for producing chips for yard maintenance.
The tree grinder is a professional-grade woodchipper that usually uses a high-speed disk chipper to break down wood. The disk chipper can feature teeth (in-between the blades) for grinding wood stumps into chips. It is also called a stump cutter or stump grinder.
This equipment is designed to be used by professionals because of its safety profile (it can cause serious bodily injuries if used wrongly).
Even so, the principle for using the wood chipper, wood shredder, and tree shredder remain the same.