Understanding Wood Behavior, Rigging Forces, and Safe Cutting Practices

This manual is designed to help climbers and ground personnel understand the principles of safe rigging operations.

Rigging is more than attaching a rope and making a cut.

Every rigging operation involves:

– Gravity

– Wood fiber behavior

– Rope angles

– Load distribution

– Dynamic forces

– Tree structure

A climber who understands these principles can remove pieces safely and predictably.

A climber who does not understand these principles may create unnecessary hazards for themselves, the ground crew, nearby property, and the rigging system.

The objective is simple:

Every piece should separate cleanly, move predictably, and remain under control.

Trees do not fail according to what we want them to do.

Trees fail according to physics.

Every cut should be planned before the saw enters the wood.

Before making any rigging cut, ask:

1. How will the piece move?
2. When will the rope become loaded?
3. How much force will be created?
4. Can the spar handle that force?
5. Are there obstacles below or beside the piece?
6. What happens if the piece does not behave as expected?

If these questions cannot be answered confidently, stop and reassess.

Not all species behave the same.

Some species separate cleanly.

Others contain long fibers that continue holding after most of the wood has been cut.

Examples:

– Hickory

– Elm

– Ash

– Sweetgum

– Certain hardwood species

These long fibers can remain attached after the hinge begins to fold.

Professional Term:

Fiber Pull

Simple Explanation:

The wood acts like a bundle of ropes. Even after most of the cut is complete, long fibers continue holding the piece together.

When those fibers continue holding after movement begins, they can:

– Tear instead of separate

– Split the spar

– Shock-load the rigging system

– Create unpredictable movement

– Damage equipment

– Cause injury

A spar split occurs when forces travel down the stem and tear the wood fibers below the cut.

Common causes:

– Inadequate notch depth

– No side relief cuts

– Uneven hinge wood

– Excessive holding fibers

– Long-fiber species such as hickory

– Excessive rigging forces

– Existing defects in the spar

A spar split can extend below the pulley or rigging block.

If the split reaches the rigging point, the entire rigging system may lose support.

This can result in complete loss of load control.

Professional Term:

Relief Cuts

Simple Explanation:

Small cuts placed on both sides of the stem to stop long fibers from tearing downward.

Benefits:

– Cleaner separation

– Reduced fiber pull

– Reduced spar damage

– Better control

– Less chance of splitting

Relief cuts are especially useful when working on species known for stringy or long fibers.

The notch controls rotation.

A notch that is too shallow may:

– Restrict movement

– Cause tearing

– Increase fiber pull

– Increase splitting potential

The notch should be large enough to allow the piece to rotate freely before excessive holding fibers develop.

A properly constructed notch allows predictable movement.

Professional Term:

Hinge Wood

Simple Explanation:

The strip of wood left between the notch and back cut that controls movement.

The hinge acts like a steering wheel.

A proper hinge:

– Controls direction

– Controls rotation

– Reduces sudden movement

– Improves predictability

An uneven hinge can cause:

– Twisting

– Side movement

– Fiber pull

– Unpredictable release

Common mistakes:

– Cutting too slowly

– Using partial throttle

– Uneven cutting

– Leaving excessive holding wood

– Not understanding species characteristics

The climber should know exactly how the piece will move before beginning the back cut.

The back cut should be deliberate and controlled.

Never rely on luck.

Professional Term:

Dynamic Loading

Simple Explanation:

Shock force created when a falling piece suddenly loads the rope.

Dynamic loading increases when:

– The piece falls farther

– Rope slack increases

– Pieces are oversized

– Negative rigging is used

Every foot of free fall increases force.

Reducing free fall reduces force.

Professional Term:

Positive Rigging

Simple Explanation:

The pulley or rigging point is above the piece being cut.

The rope begins supporting the load almost immediately.

Advantages:

– Lower forces

– Less shock loading

– Better control

– Reduced spar loading

– Easier lowering

Whenever practical, positive rigging is often preferred because it places less stress on the tree and equipment.

Professional Term:

Negative Rigging

Simple Explanation:

The pulley or rigging point is below the piece being cut.

The piece falls before the rope catches it.

This creates larger forces than positive rigging.

Negative rigging produces:

– Dynamic loading

– Shock loading

– Higher spar forces

– Higher rigging point forces

– Greater rope loading

Because of these forces, negative rigging requires careful planning and precise cutting.

A common mistake is placing the attachment point too high above the cut.

This increases:

– Rotation

– Rope stretch

– Slack

– Shock loading

General guideline:

Keep the attachment point as close to the cut as practical unless another objective requires a different tie point.

This reduces:

– Free fall distance

– Rope stretch

– Dynamic loading

– Uncontrolled movement

There is no single correct location to attach the rope.

The tie point is selected based on the desired movement of the piece.

Professional climbers choose tie points intentionally.

Beginners often tie wherever it is easiest.

The rope is attached near the outer end of the limb.

Purpose:

– Makes the butt end hang downward

– Creates vertical orientation

– Helps clear obstacles

– Protects structures below

Common Uses:

– Roofs

– Fences

– Landscaping

– Utility lines

Tip-tied pieces often rotate into a more vertical position.

The rope is attached near the center of gravity.

Purpose:

– Reduces rotation

– Reduces swing

– Creates stability

– Improves control

Common Uses:

– Tight removals

– Narrow openings

– Areas with multiple obstacles

Balanced ties help maintain a predictable load position.

The rope is attached close to the cut.

Purpose:

– Allows the tip to move first

– Helps guide rotation

– Helps direct movement

– Can improve clearance through tight spaces

Common Uses:

– Steering pieces through openings

– Controlling limb orientation

– Influencing swing direction

The closer the rope is to the cut, the more freedom the tip has to move.

Professional Term:

Center of Gravity

Simple Explanation:

The point where the piece naturally balances.

Every limb has a center of gravity.

The location of the rope in relation to that center determines:

– Rotation

– Swing

– Stability

– Load orientation

Before tying a piece, identify where the weight is concentrated.

The center of gravity often determines how the piece will behave after separation.

For negative rigging operations, a common setup includes:

1. Half hitch or clove hitch placed near the cut.
2. Running bowline or cinching knot placed above.

Benefits:

– Better control

– Reduced rotation

– Better load alignment

– More direct force transfer

– Reduced shock loading

The rope should run directly into the pulley.

Avoid:

– Running around branches

– Running around stubs

– Running around rough bark

– Unnecessary bends

Every bend creates friction.

Excessive friction:

– Wears equipment

– Reduces efficiency

– Increases loading

– Creates unpredictable rope behavior

A straight rope path is always preferred.

The spar is part of the rigging system.

Before rigging, inspect for:

– Cracks

– Decay

– Cavities

– Previous splitting

– Weak unions

– Old wounds

– Dead wood

The strongest rigging equipment cannot compensate for a weak spar.

Rigging requires communication.

Before every cut:

– Climber and ground crew acknowledge readiness.

– Commands are clear.

– Everyone understands the plan.

– Everyone understands the landing area.

Never assume communication has occurred.

Confirm it.

✓ Rigging point inspected

✓ Spar inspected

✓ Rope path clear

✓ Ground crew ready

✓ Communication confirmed

✓ Notch complete

✓ Relief cuts completed when necessary

✓ Proper tie point selected

✓ Landing zone identified

✓ Escape position planned

✓ Forces understood

✓ Obstacles identified

If any item is uncertain, stop and reassess.

Professional climbers do not simply cut wood.

Professional climbers understand:

– Gravity

– Wood fibers

– Species characteristics

– Hinge mechanics

– Center of gravity

– Rope angles

– Dynamic loading

– Tree structure

Every cut should have a purpose.

Every tie point should have a reason.

Every piece should move in a predictable manner.

The goal is not just to remove the tree.

The goal is to remove the tree safely, efficiently, and under control