What is the optimum lawn mower blade angle/pitch?

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Old 04-10-11, 08:48 AM
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What is the optimum lawn mower blade angle/pitch?

I have a generic 6hp push mower from Sears. When all four wheels are correctly set for the same height the blade is one half inch lower when it passes between the front wheels than when it passes between the rear wheels.

Is this done on purpose, or did I just get a sloppily engineered mower?

Specifically, should the blade rotate perfectly parallel to the lawn surface, or is the blade supposed to be tilted down in front for some reason?
 
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Old 04-10-11, 10:58 AM
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I found the answer on another forum:

"The slight foreward tilt to a rotary mower deck is done to save horsepower, and to reduce clogging and matting inside the deck. It will also give a much better shear to the grass blades and reduces exploded tips on the grass.

If a rotary mower deck is adjusted with the front slightly higher than the rear of the mower, and of course the blades arc are then a bit higher in front, so the grass is cut off at say 31/4 inch high at the front of the mower, then as the deck travels on across this grass and it finally gets under the rear edge of the deck , here comes the blades again , and the blade is cutting at the lower 3 inches on the backside of its swing. This means that the grass gets mowed again [just 1/4 inch] but it really kills your power to mow off say 60 inches of grass in front and then mow another sixty inches of the same grass again just as it exits the rear edge of your deck.

The second bad thing that happens is that the clippings are cut and thrown out the chute by the swing of the blades at the front end of the mower, but the grass that gets a second cutting at the rear of the blade arc is all tossed the WRONG WAY. This grass is all blown over into the closed in left rear corner of the deck, where it matts and sticks to plug up your deck, it then falls out as wads and clumps of finely chopped grass. The lawn then begins to look like a goat puked all over it.

The third bad thing that can happen from reversed pitch on a mower is that grass blades that are cut off at the very tip end of the blade [last 1/8 inch] will often explode the leaf tip of the grass. This is especially a problem with Kentucky Blue grass.
If you look closely at the grass tips, they will look like the end of a bull whip that has been cracked till it's shredding. The grass will then get a yellow unhealthy look all over the lawn, not the deep green vibrant appearance you want after you have mowed it. This damage can happen even from a mower that is set dead level. The blade RUBBING the grass tips can explode the grass leaf tip. This is why they recomend a 1/8 to 1/4 inch foreward tilt to all rotary mower decks - so that the blades on the back side of the swing never touch or cut the grass at all. If you set your deck correctly with just a touch of foreward tilt , then all these problems just go away !!!"
 
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