Poorly ground mowers tend to flail and tear the grass leaving bleeding rough edges
It’s not exactly a “new” technology.
In the late 1800’s the company now owned by Bernhard’s began building machines to grind and sharpen cylinder. By the turn of the century a range of four steam-driven grinders had been developed and they were selling hundreds of machines annually. In the mid-1900’s it became apparent how critical cylinder and bottom blade sharpness was. This was later re- affirmed by research carried out in the 1970’s. During that time an enormous amount of time was spent learning what went into producing superior turf conditions and how much mower sharpness influenced those results.
WHY do sharp mower blades play such an important role in mower maintenance and turfgrass health?
To begin dissecting this question we need to first establish the difference between a surgical or scythe cut and a scissor-cut and the effects of each. Scissors require two blades travelling in opposing directions which will cut adequately if there is sufficient light contact along the length of the two blade edges. A scythe consists of a single cutting blade being drawn through the leaf tissue, damaging fewer cells in the process. Scissors will cut, but a scythe cuts better. In a cylinder mower, one difference between a scythe
and scissors action is the velocity of the cutting edge moving down the bottom blade. A properly ground and adjusted mower will operate in a scything action at up to four times the efficiency of an improperly ground or misadjusted cylinder functioning as scissors. As the bottom blade is an equal partner with the cylinder blade in the cutting process, equal consideration must be given to proper grinding and in-season maintenance of the front and top faces of the bottom blade. If the bottom blade is not sharp and true, the cylinder blades will encounter inconsistencies travelling along it, resulting in an imperfect cut.
Even the most precise angles and adjustments can
go awry if not maintained properly once the cylinder and bottom blade start to wear.
The single blade grinding method, made popular in the United States earlier in this century, applied varying levels of cut to each cylinder blade, resulting in an imperfect cylinder. Lapping was invented to make a single-blade-ground cylinder truly cylindrical again. Very simply, oil was mixed with sand and lathered on to the cylinder while it turned backwards (so the high cylinder blades wouldn't bang into the bottom blade). During the lapping
process, the abrasiveness of the sand wears down the high blades to the level of the low ones, but also creates two curved, mirrored surfaces
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