English gardeners once had their famous grass with hand shears: a tedious operation, but with excellent results.
The regrowth of a grass with very fine grasses, which gives a lawn a "velvet" appearance, is better when the grasses are cut clean. (Non-contractual photo, does not necessarily reflect the drawing)
They then push back immediately, without experiencing a phase of yellowing-drying of the cut ends, as is the case with all systems that "chop" the grass. The system of blades with shearing teeth of the mechanical mowers is the one that gives the result closest to the grass shears. But he is unable to mow as smoothly and regularly as a mower.
It is the helical blade machine that gives the best results. This system is widely used in Great Britain, the United States and the Netherlands and is not commonly used in France except on hand mowers, all of which are cutting cylinder type and large professional mowers. They have two or even three cutting cylinders front each side is lift to avoid obstacles.
The cutting cylinder has 4 or 6 blades in the form of a propeller blade at very large pitch, fixed at each of their ends on circular flanges. The whole constitutes a cutting cylinder rotating around a horizontal axis. A horizontal fixed counterblade, also called anvil, is at the bottom.
During rotation, each helical blade passes along this anvil rubbing. This creates a phenomenon of shearing the grass. In addition, the friction of the cutting lip of each blade on the edge of the anvil causes the automatic regreasing of the blades. The helical shape of the blades is maintained by spacers fixed on the horizontal axis which drives the cutting cylinder.
The helical blade cutting system finds its optimal efficiency when blades rotate at a constant speed. Most mowers of this type include a system driving the cutting cylinder from the rollers or the roller that carries the cylinder.
This is always the case on hand mowers. The drive is usually entrusted to a chain connecting solidarity pinions respectively of the axis of the support drum and the axis of the cylinder. Such a cutting cylinder driving device is also found on a few low power self-propelled machines, where the mower motor serves only to drive the rear wheels of the machine.
However, on the most powerful mowers, the or more often the (there are then two or three) cutting cylinders are driven mechanically, from the engine which also ensures the propulsion of the mower. Ride-on lawn mowers are almost always type propulsion (rear-wheel drive). But there is also traction, a single wheel at the rear, ensuring direction.
The transmission of the movement to the cutting cylinders requires a relatively complex device. The most commonly used comprises a horizontal drive shaft, carrying at each end a pinion which drives, by chain, each cutting cylinder. This intermediate shaft is itself driven by chain, or sometimes by a longitudinal transmission shaft, from the output of the gearbox; this requires the use of a conical return, except on the few machines driven by a horizontal motor.
The self-sharpening of the blades is ensured by the friction on the anvil; it remains pressed on the cutting cylinder by springs placed around the fixing columns of the anvil. It must be ensured that the anvil can always struggle, that is to say that springs and balusters do not rust, lubricating them from time to time. It will also be ensured that the advancing lip of the anvil remains straight. It must be straightened if it has been damaged by a stone and grind it if it is chipped; in the latter case, the adjustment will be resumed to guarantee self-sharpening friction. To straighten a helical blade, use a mallet and a bunch of American coachbuilder (kind of small hammer).
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