Harvester Head Product

Overview

The harvester head is a mounted processing unit that debarks, delimbs, and bucks felled logs to marketable lengths. It is hydraulically driven and attached to the boom of a harvester base machine (tracked or wheeled). The harvester head integrates several hydraulic motors and powered components: a Feed System draws logs in at controlled speed, a rotating Delimb Unit removes branches, a Saw Unit bucksaws the log to length, and an encoder-based Measuring System system triggers cuts automatically.

Harvester heads enable one-operator processing of entire trees at the stump, transforming raw stems into market-ready logs without secondary chipping or debarking equipment. They are essential to single-grip harvesting systems used in mechanized forestry worldwide.

How it works

The harvester head is mounted on a boom arm via heavy Connector Plate pads bolted to the Main Frame Casting. The base machine operator controls the head via proportional pilot signals transmitted through hoses from the cab to a Hose Manifold distribution block integrated into the frame casting.

Logs enter the head vertically aligned along the feed axis. The Feed System consists of a top Top Feed Roller powered by a Feed Motor and a bottom Bottom Feed Roller spring-loaded against it. As the Feed Motor spins, the rollers grip the log and draw it forward at 0–5 m/min, controlled by the operator's proportional foot pedal.

As the log advances, it passes through the Delimb Unit, where six hardened Delimb Knife blades mounted on a rotating Knife Rotor strip branches from the stem. The Delimb Motor drives the rotor at 300–500 rpm, and the spring-loaded knives follow the log contour, removing all side branches. Debris falls away from the machine due to the rotor centrifugal action.

Once debarked, the log advances to the Saw Unit. Here, a bi-metal Bandsaw Blade driven by the Saw Motor at 1500 rpm engages the log. The Measuring System system detects the log length as it moves: the Measure Wheel presses against the log, and each rotation generates a pulse from the integrated Encoder. When the accumulated pulse count reaches the set length (typically 2–8 m), a solenoid pilot valve triggers the Blade Tensioner to retract slightly, lifting the saw blade and allowing the bucked log to fall onto an ejector conveyor or ground pile.

The entire head rotates ±180° via a Rotator Motor with integral gearbox, driven by proportional pilot signals. This rotation capability allows the operator to orient logs laterally for optimal flow through the delimbing and bucking zones, improving feed uniformity and reducing jams.

Feed and Delimbing Subsystems

The Feed System uses a closed-loop motor control: the Feed Motor is a fixed-displacement unit receiving proportional pilot pressure. The top roller is coated with a 5 mm elastomer layer to grip logs without slipping while minimizing marring. The bottom roller is spring-loaded to maintain constant contact pressure as logs of different diameters pass through.

Four Roller Bearing pillow blocks on the Main Frame Casting support both rollers, sealed and rated for continuous water exposure (in wet climates, harvester heads operate in rain). The Drive Shaft couples the motor to the top roller via universal joints, accommodating slight frame deflection under load.

The Delimb Unit comprises a Knife Rotor rotating at 300–500 rpm. Each of the six Delimb Knife blades is hardened tool steel with a replaceable cutting edge. As the log passes through the rotor's diameter, the knives shear off branches flush to the stem. The rotor is supported on a large Rotor Bearing slew bearing that absorbs the radial and bending forces from branch cutting. Dulled knives are removed and replaced without disassembling the head—a typical maintenance interval of 400–600 operating hours.

Bucking and Measurement

The Saw Unit uses a bandsaw rather than a circular saw in most modern designs, as the kerf is narrower (1.6 mm vs 4 mm), reducing product loss. The Bandsaw Blade runs at 1500 rpm, cutting through the stem at a feedrate of 2–5 m/min (automatic with the log push). The Saw Frame uses hardened steel guide bushings to keep the blade straight and prevent deviation, critical for clean crosscuts.

The Blade Tensioner maintains 500–800 bar blade tension via a hydraulic cylinder that pushes a spring-loaded idler pulley. Loss of tension automatically halts the feed motor (a safety interlock) to prevent blade breakage.

Length measurement is based on the Measure Wheel, a precision-ground 250 mm diameter wheel pressed against the log by a spring Measure Mount. Every rotation registers 785 mm of log advance. An integrated Encoder outputs a 4–20 mA signal proportional to rotation; a simple analog accumulator or PLC counts pulses and signals the bucking blade to retract when the target length is reached. Typical accuracy is ±10 mm per cut, acceptable for log grading and trucking constraints.

Rotation and Integration

The Head Rotator allows the entire head to twist ±180° around its boom-mounting vertical axis. This is driven by the Rotator Motor, a bent-axis motor with a 20:1 reduction gearbox, rotating at 60 rpm. Rotation is critical when logs have crooks or taper asymmetrically, allowing the operator to feed them optimally through the delimbing and cutting zones without jams.

The Main Frame Casting is a large ductile iron body integrating all bearing pockets, hose manifolds, and structural load paths. The Hose Manifold distributes pilot oil from the boom via a single umbilical hose bundle, eliminating external plumbing and reducing leak points.

Performance and Maintenance

A modern harvester head processes 8–15 logs per minute depending on log diameter and set length. In a typical shift, a fully-equipped harvester (tracked frame + boom + head) can process 8–12 tonnes of standing timber into market logs. The Feed Motor, Delimb Motor, Saw Motor, and Rotator Motor are all proportional-pilot controlled, allowing infinite speed modulation from zero to maximum.

Maintenance is minimal: filter the hydraulic tank every 200 hours, replace knife edges every 400–600 hours, inspect blade tension and bearing play annually. Harvester head designs from Komatsu, John Deere, and Husqvarna dominate industrial harvesting due to proven reliability and interchangeability with base machines.