String Trimmer

Overview

A string trimmer (weed-eater) cuts grass and weeds with a fast-spinning nylon line rather than a blade, so it can work along edges, fences, and obstacles a mower cannot reach. This model is a petrol straight-shaft unit: a 2-stroke engine at the top drives the cutting head at the far end through a long drive shaft and a right-angle gearbox.

The Power Head holds the Engine Assembly, a 25.4 cc air-cooled 2-stroke, and a Clutch Assembly. The engine is fed by an all-position Diaphragm Carburetor that meters fuel against crankcase pulse pressure, draws fuel from the Fuel Tank, and fires through a flywheel-magneto ignition. A Recoil Starter spins the flywheel to start it.

How it works

Above idle, the centrifugal clutch's shoes fling out and grip the drum, coupling the engine to the Shaft Assembly. A flexible steel drive cable runs the length of the aluminium tube on liner bushings, carrying rotation down to the Gear Head. There a bevel gear pair turns the drive 90° and reduces its speed before the cutting head.

The Trimmer Head is a bump-feed design: monofilament line spun at speed cuts the vegetation, and tapping the bump knob on the ground pays out fresh line through hardened eyelets as the working ends wear away. A Debris Guard shields the operator from thrown debris and carries a blade that trims the line to length.

Construction

The operator supports and aims the tool with the Handle Assembly, a loop handle clamped to the shaft carrying the throttle trigger and ignition kill switch; a Bowden cable links the trigger to the carburetor. A padded Shoulder Harness slings the tool's weight off the shoulder, and a common Fastener Set secures the assembly.