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How Does a Wood Chipper Work? A Guide to Wood Chipping Mechanisms

Wood chippers are an essential tool for reducing wood debris and turning it into mulch or fuel. But how exactly does this powerful equipment slice, dice and shred wood and branches? In this comprehensive guide, we’ll take an in-depth look at the inner workings of wood chippers to understand the engineering and science behind these machines.

An Overview of Wood Chipper Designs

There are two main types of wood chippers: disk and drum. Disk chippers use a spinning metal disk with blades to cut up wood, while drum chippers utilize a horizontal drum with blades to chip and shred material. Disk chippers are more common for residential use given their lower cost and smaller size. Drum chippers on the other hand tend to be larger commercial models best suited for heavy-duty chipping jobs.

The basic parts of both disk and drum wood chippers include:

  • Feed system – this is the opening or chute where branches and wood debris are fed into the chipper. Some models have powered feed rollers to help pull material in.
  • Cutting mechanism – either a metal disk or drum lined with hardened steel blades that rotate at high speeds to chip the wood.
  • Screen – perforated metal screen of varying sizes to filter out wood chips, allowing properly sized chips through while keeping oversized pieces within the cutting area for further chipping.
  • Discharge chute – where the finished wood chips exit the chipper and can be collected.
  • Engine system – provides power, usually via a gas engine, hydraulic motor or electric motor. More robust commercial chippers may have 200 HP or larger engines.

Now let’s look at how these components work together inside wood chippers to chip and mulch wood material.

How Wood Gets Chipped by the Cutting Mechanism

The magic happens with the cutting mechanism, whether it be a spinning disk or rotating drum lined with razor-sharp blades. This is what actually cuts and shreds the wood into small chips or mulch.

Disk chippers use a circular metal disk approximately 20-30 inches in diameter, spinning at speeds usually between 1000-3000 RPM (revolutions per minute). Knife blades are bolted onto the disk, numbering from 2 blades for smaller 5 HP chippers up to 4-6 blades for 20+ HP commercial models.

The disk spins rapidly, bringing wood fed into the hopper down onto the disk where the blades slice into the material. The kinetic energy of the fast rotating disk coupled with the sharp blades applies immense shearing forces that quickly slice wood into chips.

Drum chippers contain a horizontal metal drum 25-40 inches in diameter lined with blades and spinning at 500-1400 RPM. The drum pulls wood through and chops it up with the blades as it rotates. Having more length than a flat disk, drum chippers can process wood faster.

Hardened steel blades are essential in both types for chipping wood efficiently without quickly becoming dull. These short and long blades can be removed and sharpened or replaced over time. Self-feeding chippers will use powered rollers before and after the cutting mechanism to pull wood through automatically.

How the Feed System Works

Feeding wood and branches into a chipper must be done with care given the high-speed cutting blades inside. Self-feeding chippers make the process easier, using a system of rollers before and after the chipper blade to grab and pull material through automatically once engaged.

For manual feed chippers, the operator must carefully and safely insert wood into the feed chute and hopper. Longer pieces may need pushing through to reach the cutting mechanism. Feed hoppers utilize gravity so wood falls into the blades. For disk chippers, hoppers are oriented vertically and they lay horizontally for drum chippers due to the shape and orientation of the cutting mechanism.

Powered feed roller systems are common in larger drum chippers. Feed rollers before the drum grab and pull material through, working with additional rollers after the blade to keep drawing wood through the drum. This makes processing larger branches and trees more automated and efficient.

Safety sensors are integrated into self-feeding systems to stop them if pull-in sensors detect something wrong. Operators should always wear protective equipment when running any wood chipper and follow safety procedures. Small disk chippers for residential use are often manual feed only given their more occasional usage.

Why a Screen is Critical in Chippers

Integrated screens are a critical component for wood chippers to function efficiently. The screen acts as a filter, allowing properly sized chips through while keeping oversized pieces within the cutting area for further size reduction. Screens come in various sizes with perforations ranging from 1/4-inch to over 2 inches, depending on desired chip size.

Without a screen, chips could be randomly sized with more undesirably large pieces getting through. The screen ensures the discharged chips are sized to whatever the specifications and needs are. For example, a 3/8-inch screen will allow chips smaller than that through while retaining chips over 3/8-inch to be further processed by the blades into smaller pieces.

Self-feeding chippers usually have the screen integrated after the drum or disk cutting mechanism. It may consist of a grate screen in a tray below the mechanism or a cylindrical screen surrounding the drum. Manual feed models require vigilance by the operator to ensure overly large pieces unsuitable for the screen size are minimized.

Proper screen maintenance and cleaning is crucial to prevent clogging, which can lead to jamming. Clogged screens reduce efficiency and increase wear on chipper blades and parts as material builds up.

Why Proper Maintenance Is Vital for Chippers

Given the high-speed cutting blades and robust mechanical systems operating in wood chippers, proper maintenance is vital for efficiency and longevity. Following the manufacturer’s maintenance guidelines is highly recommended. Here are some key maintenance tips:

  • Check/replace chipper blades – Blades should be inspected routinely for dullness or damage and rotated or replaced as needed to keep edges sharp.
  • Lubricate parts – All grease fittings and friction points should be regularly lubricated. This includes gear boxes, bearings and drive systems.
  • Check belts/chains – Inspect and tighten belts and drive chains as needed. Replace worn belts/chains.
  • Clean machine & screens – Clear any debris buildup and clean feed rollers and discharge chutes. Clean screen to prevent clogging.
  • Check hoses & fluids – Ensure hydraulic fluid levels are adequate. Inspect hoses for wear/damage. Check engine oil levels.
  • Inspect moving parts – Check for excessive wear on rollers, bearings and bushings. Replace as required.
  • Check safety features – Confirm all guards are in place and interlock safety systems are functioning.

Proper maintenance will extend the machine’s lifespan, maximize performance and processing capacity, and prevent breakdowns or unsafe operation. Consult the owner’s manual and follow the manufacturer’s recommended maintenance schedule.

Key Factors That Affect Chipping Performance

Several important factors impact how efficiently a wood chipper can chip and process material:

  • Engine Power – Horsepower determines chipping capacity. More HP supports larger material and higher volumes.
  • Blade Sharpness – Sharp blades are crucial for fast, easy chipping without jamming. Dull blades slow production.
  • Material Moisture Content – Green wood with over 30% moisture content is more difficult to chip than seasoned wood.
  • Material Size/Shape – Chippers have capacity limits. Exceeding those leads to jamming. Odd shapes also increase chances of clogging.
  • Feed Rate – Match feed rate to engine RPM to maximize production without overload. Don’t exceed capacity.
  • Maintenance – Well maintained machines will outperform neglected ones with dull blades or mechanical issues.

Understanding these dynamics allows matching the right chipper design and size to the intended chipping application and materials. A lower powered chipper overloaded with wet gnarled branches will produce poorly compared to a high capacity model chipping dry straight softwood.

Safety Tips for Working with Wood Chippers

Operating a wood chipper requires great care as the cutting mechanisms are very hazardous. Safety precautions when using chippers include:

  • Never reach into the feed hopper while operating or try to unclog by hand. Immediately turn off before clearing jams.
  • Wear close-fitting protective clothing without strings or loose items that could get caught in moving parts. Use eye and hearing protection.
  • Avoid feeding material larger than capacity or with protruding nails which can break blades and cause kickback. Cut to size first if needed.
  • Maintain a safety zone around the machine and never allow bystanders nearby while operating.
  • Be attentive and avoid distractions. Don’t let equipment run unattended.
  • Keep discharge hood pointed away from people, animals or objects. Beware flying debris.
  • Ensure machine is on stable, level ground and tow vehicle brake is set before running.
  • Follow manufacturer safety procedures and don’t remove guards. Shut off engine before servicing.

Staying alert and using common sense goes a long way toward safely operating wood chippers. Respect the equipment and follow safety protocols.

Frequently Asked Questions About Wood Chippers

What size chipper do I need for home use?

For residential usage, a smaller 5-10 HP disk chipper is usually adequate. Compact and portable models can handle branches up to 3-4 inches diameter. Larger 15 HP+ machines are only necessary for very high volumes.

How long should wood chipper blades last?

With proper care and maintenance, wood chipper blades should last 50-100 hours before needing sharpening or replacement. Harder wood species and dirty material will wear blades faster.

What safety equipment should be used with a chipper?

At minimum, operator safety equipment should always include: close-fitting clothing, leather gloves, hearing and eye protection, steel-toe boots, and a helmet/hard hat if handling larger branches above shoulder level.

How do you clean out a clogged wood chipper?

Never use hands or tools while blades are moving! The machine must be turned off and power disconnected before clearing jams by hand. Refer to manufacturer’s procedure for your model. Always take measures to avoid clogs when operating.

What is the difference between disk and drum chippers?

Disk chippers have a flat, circular spinning disk with blades to cut wood loaded vertically into a hopper. Drum chippers use a horizontal cylindrical drum with blades that wood passes through horizontally. Drum chippers are faster but more expensive.

Can you sharpen dull wood chipper blades yourself?

Yes, chipper blades can be removed and sharpened using a grinder or file. However, it takes skill to properly resharpen blades to the correct specifications. Most owners utilize professional sharpening services annually to keep blades factory-sharp.

How often should you grease and service a wood chipper?

Routine service should follow the manufacturer’s recommendations for lubrication, belt tension, blade maintenance, and other upkeep. Most chippers require greasing bearings and pivot points every 25-50 hours of operation as well as regular inspection of blades.

What safety mechanisms do some chippers have?

Higher end chippers may incorporate safety features like hopper access interlocks, emergency stop cords/buttons, feed control bars, and discharge chute sensors. Basic disk chippers rely primarily on the operator’s attentiveness and vigilance when feeding material.

Can you rent wood chippers?

Yes, wood chippers are commonly available for rental from equipment rental companies. Gas powered chipper rentals range from smaller 6-10 HP units for homeowners up to large 25 HP+ industrial models. Rental rates are typically per day or half-day.

Key Takeaways on How Wood Chippers Work

  • Disk and drum chippers use high-speed steel blades to efficiently chip wood material fed into the unit.
  • Robust feed systems include rollers to grab and pull wood material through chippers automatically.
  • Integrated screens filter out sized chips and retain oversized pieces for additional chipping.
  • Sharp blades, adequate power, and proper use/maintenance are crucial for optimal chipping.
  • Safety is paramount when operating chippers due to hazards posed by the cutting mechanisms.
  • Routine maintenance and blade care maximizes performance and longevity of wood chippers.

Understanding the internal workings of wood chippers – from feed systems to cutting mechanisms to screens – provides insight into how these machines operate to shred and chip wood material into useable chips and mulch. Proper use and maintenance keeps wood chippers functioning safely and efficiently.

Laura Kassovic

Laura Kassovic, a former engineer at Intel SOC, now dedicates her efforts to mentoring startups in the realms of Wearables and AI. As a co-founder of New Tech Brake, she spearheads a wireless sensing solution enterprise catering to diverse applications including product development, research, location tracking, and people monitoring, as well as asset and cargo supervision. The platform empowers developers to craft an array of innovations such as fitness trackers, temperature-monitored cargo systems, medical trial tools, smart running garments, or even straightforward transmission of unprocessed accelerometer data to cloud-based repositories.

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