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self sharpening lawnmower blades

perpetual razor sharp mowing edge
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Make the mower blade the same way as those handy self-sharpening knives. The more grass, dirt, rocks and cats you mow over the sharper the blade gets.

Self sharpening blades are typically made by applying a coating or heat treatment to only one side of a blade making that side extremely hard and brittle so that chips and wear to the edge result in a new edge, just as sharp. But such a treatment for mower blades might make them overall too brittle to be practical.

So my other idea is to make the mower blade like a giant horizontal pizza cutter wheel. It can be serrated to increase cutting power, but the bevel for the sharp edges will be on the top only. That means it can be sharpened by lowering a honing stone onto the top edge of the blade, at the correct angle. The stone will be permanently installed in the mower, and can be lowered by a manually operated lever for a quick re-sharpening while mowing. The fancy models would have timed devices to periodically lower the stone automatically.

ServoMan314, Jun 26 2008

illustration of my suggestion http://usera.imagec...owersharpen.bmp.jpg
plan and cross section diagram. The blade (blue) rotates in the plan. The sharpening stone (grey) pivots in the cross section. [xaviergisz, Jun 26 2008]

Another take on it. http://www.freepate...ower%22&stemming=on
[2 fries shy of a happy meal, Jun 26 2008]

[link]






       I don't think the pizza wheel version would cut the grass very effectively.   

       It may be possible to retro-fit a sharpening device into an existing lawn mower. Basically this would be a sharpening stone that is pivotally connected to the lawn mower. As the blade rotated, the leading face of the blade would rub across the sharpening stone while also pushing the sharpening stone. see illustration.
xaviergisz, Jun 26 2008
  

       [servo] do you work at wimbledon by any chance?
po, Jun 26 2008
  

       [po] I'll bite. No, I dont work at wimbledon. why?
ServoMan314, Jun 26 2008
  

       servoman + grass !
po, Jun 26 2008
  

       A single pizza cutter or deli slicer wouldn't work, the grass would just slide under, but twin pizza cutters would. You could then add in a stationary sharpening wheel at the center to sharpen both and slowly rotate the sharpened part out to cut the grass.
MisterQED, Jun 26 2008
  

       [po] oh, i get it. its actually "servo" as in a closed loop positioning actuator. long story...
ServoMan314, Jun 30 2008
  

       You could probably do something with laminated metal. As the cutting force increased (due to difficulty in cutting the grass, a layer would peel off, exposing the new undamaged layer. Dealing with a strip of metal at high speeds would be a problem though.
MechE, Jun 30 2008
  

       Lawnmower blades aren't actually 'sharp' as in knife sharp. The 'cutting' of the grass is more like smashing of the turgid grass leaves by impact of the (relatively) massive kinetic force of the blades.
ConsulFlaminicus, Jun 30 2008
  

       //Lawnmower blades aren't actually 'sharp' as in knife sharp//   

       Lawnmower blades aren't made to be sharp because they blunt too quickly. If lawnmower blades could be made to retain a shape edge, they would cut much more effectively than typical flat-edge blades.
xaviergisz, Jun 30 2008
  
      
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