Sharp rotating blades shear grass and the cutting action is mostly caused by the outer-most square corner formed by the cutting edge and blade's end - and then the first two inches of blade's cutting edge are the next most important aspect. Velocity may spin the blade, true, but it is not velocity which cuts - it is the cutting tip and cutting edge which perform this task.
To inspect for fissures (cracks that don't go all the way through) and cracks requires blades to be perfectly cleaned.
Flatness needs to be checked with a rotational gauge.
Anything which rotates at speed needs to be balanced for all of its components to have longevity. Even ceiling fans, and they spin at far, far, slower RPMs.
Inexpensive blades are being made from milder steel and do not hold a cutting edge for long and do not endure impact(s) as well. They fracture more easily and suffer damage far easier.
Having said this, we find name brand blades are often poorly balanced. Spindles are not cheap. Balncing with a precison tool such as the Magna-Matic 1000 is what many shops use. Chinese knock-offs of the M-M 1000 lack the precison bearings (we have used them) and therefore do a lousy job when compared to the M-M 1000.
We have seen blades from single blade equipment that have trashed the mower's bearings due to homeowner's sharpening and balancing with the wrong methods. It does not happen overnight, but it can in time. For the past few years one customer new to us this year had been shapening and "balancing" the three blades in his J-D deck. He had to replace all three spindles last year due to his blade maintenance routine. And these blades are shorter than some single-blade walk-behinds. It is not always blade weight, as blade mass is spread out over the length of the blade. More to the point is the length for when a blade is near to or out of flatness spec (far more important with length) balance now becomes increasingly important.
The comments made here and in prior posts are all with respect to rotating (i.e. NON-REEL) blades.
We no longer see many reel mowers around as these are typically owned by golf courses who maintain their own equipment. The last residential reels (at least around here) began to drop out of view in the mid 60s and were pretty much gone by the late 70s. By the mid 1980s we stopped servicing reel mowers. There are still a few companies who still make machines for sharpening reel assemblies.
As for rotating blades, we feel there is but one manufacturer who makes the best equipment for sharpening ALL (rotating) blade types, be they flat, mulching ("curvy", "wavy"), high lift, or gator-style blades as their equipment is the only machinery which can produce a uniform full cutting edge long, consistent angle, machine produced edge. All others require removal from the machine to finish the curved/high-lift/wavy/gator portion of the edge as these other products can only machine sharpen the flat portion of the blade's cutting edge. And this equipment is the Magna-Matic 8000 (Note: not the M-M 9000 model).
