A high-tonnage press pulls a flat sheet of steel into a deep bowl with no joints in one stroke. The curves and domes stiffen the shell, so thinner steel can behave like thicker plate. Heavy commercial decks are instead laser cut and welded from thicker plate.

Steel decks get an electrodeposited primer, then robot arms spray powder that an oven bakes into a hard skin. Grass juice, fertilizer and salt attack bare steel, and the underside fails first.

The blade is cut from steel harder than the deck and then heat-treated so it keeps an edge through sticks and stones.

Each blade is balanced to tight tolerances. Even a slight heavy end shakes the machine and wears out bearings and engine mounts.

A small one-cylinder four-stroke engine, usually bought from an engine maker, bolts to the deck with its crankshaft pointing down. The blade bolts straight onto that shaft.

Workers fit the wheels, the height-adjustment levers, the handlebar and the controls. Self-propelled models also get a transmission driving the wheels.

A discharge guard goes over the chute, and a bail lever on the handle stops the blade when the operator lets go.

Technicians check blade speed, confirm that the stop lever brakes the blade, and measure engine output before the machine is boxed.