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View Full Version : Blade tip speed on a 21"


Doogiegh
12-15-2002, 08:00 PM
Does anyone know the typical blade tip speed on a 21" mower, say a Toro 21" or a craftsman 20-21" homeowner grade stuff?

And lets say you are using blades that are 18 inches long.. How "MUCH" of the blade do you think actually does the cutting? The outside 4-5 inches on each end? so the middle 8-10 inches near the center hole really don't do much cutting, right?

How far down the ends do you sharpen? Gonna do some math on your numbers.. Thanks

Gary

Bob Minney
12-15-2002, 09:07 PM
My ariens 21" approx 18,000 fpm @ 3,000 rpm
OEM blade has 3.5" cutting edge
Gators 5"

barnard
12-15-2002, 09:50 PM
It's easy to figure on a walk behind with the blade attached directly to the crankshaft. Formula is blade lengthX3.14Xengine rpm. Example with 21 inch blade and governed engine speed of 3,600 rpm. 21x3.14=65.94 round to 66 this is inches traveled at blade tip in one revolution of engine. convert to feet by dividing by 12. This is 5.5feet per rev. Times 3,200=19,800fpm

Likestomow
12-15-2002, 09:51 PM
I only sharpen the outer 1.5" of every blade I use.

Lawn Specialties
12-16-2002, 12:55 AM
Advertised blade tip on a Toro 21" is 18500. I sharpen mine same as they come from the factory but have thought of going in further. Any body tried it?