Tuesday, June 15, 2010

April Showers And All That Jazz

“April showers bring May flowers that bloom in June...” singers croon, but we know they bring grass. Healthy, tall growing, vibrant, green grass that has to be cut on a regular basis.

I popped off the blade on my grass cutter to give it a much needed sharpening. I’m always amazed by rotary mower blades, only the tips are sharp. I always thought they would be more effective if the entire blade was razor sharp.

Not so, grass cutter man. Only the tips of the blade need to be sharpened. More on that later.

I use to take my blade into a mower shop where I envisioned a skilled certified technician (in a white lab coat, of course) who would carefully grind and polish the blade with a set of water cooled stones at some precise angle dictated by the blade manufacture. Careful to take only an equal amount of metal from both blade ends, he would constantly check the blade’s balance so it will spin true.

Not so, grass cutter man. Some guy eyeballs the edge while passing it over the course grind wheel. Sparks shoot out the back of the grinder and maybe he makes a second pass to see more sparks if he missed the fireworks last 4th of July.

I hate it when reality collides with my imagination! So I bought a disk-shaped stone with a plastic collar/guide that fits my cordless drill and now I just clap the blade in a vice and grind it myself. Then when I’m done, I can use a fine carbide stone to polish up the rough spots.

I was thinking while clamping it in the vice, how fast does the edge move? I took a measurement from the blade axle center to the leading and trailing edge. The back of the blade is 4.5 inches from the center while the leading edge is 9.5 inches. Since the blade spins at 3600 rpm that means the blade is spinning at, ahh, let’s see, 3.1415 times 0.375, carry the 7…

Wow, the front of the blade zips along at 101 miles per hour while the back of the blade is loafing along at a measly 48 miles per hour. The blade is only five inches long, so if I’m mowing an inch a second, (as a trivial exercise to the reader I let you calculate how fast I’m walking), a one inch section of the blade spins 60 revolutions over that one inch of grass.

Speaking for myself, cutting grass has a new dimension of fun!

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