A rain event

...Is what my dad would call a day like this. So while I still can't mow the lawn, I might as well sharpen the mower blade, right? Let's pump up the jams and get to it! 

Safety gear (hearing, respiratory and eye protection) is an absolute must for this!

    While it is difficult to photograph, I hope we can all agree that this blade, shown with one cutting edge in the foreground, would not cut but rather maim room temperature butter.

    Normally I might clean up the rust and pitting first, but on balance, it's probably just as cheap to purchase a new replacement blade! All we are trying to do is cut the grass, which is now a foot high and loving all this rain!

    First thing to check before putting the time in is to see if the blade is bent or warped. Let's check it against a relatively *flat* surface.

    Not perfect, but serviceable.

    From the end, we want the bottom plane of the blade behind the cutting edge to be flat. Here it is twisted, but it is twisted on my favor. This might even be part of the design of this particular blade.

First I'll "joint" the cutting edge flat, trying to grind past the depth of any major dents or chips, and relatively square to the bottom of the blade.

    The bright reflective area is freshly ground. That ding in the bottom of the blade won't be as sharp as possible until we grind back past it. I won't get it during this session, but through successive sharpenings it will diminish.

    Next I'll grind a bevel on the top o the blade only. I'll be removing quite a bit of material, so I want to periodically cool the  blade in water.

   The accidental "micro bevel" at the edge won't hurt us here. The idea is to create an angled plane that meets the flat of the bottom of the blade with as close to no surface area at the edge as possible (think of two planes meeting perfectly in space, with no radiused edge at their meeting line) It's not a drawknife, and it will cut grass fair enough, but the principles involved are transferable.

    Now to repeat the process for the other cutting edge.... 

   And possibly the most important part, balancing. An improperly balanced blade will, among other things, vibrate the mower and cause damage to the engine. Here I have rigged up the lowest drag system I could with what I have at the house: some 5/16" drill rod, some tape to make a tight fitting bushing betwem the rod and the blade, and two rails from the base of my lathe. It's not perfect, but the rails occupy the same plane, and in case that plane is out of level, I run the test in each direction, marking the heavy end with a little tab of tape.

The blade is spun slowly, and is free to rotate until it can't make a full revolution, when it rolls back the other way and creates a pendulum with the heavy en down. I'll take a chunk out of the heavy end of the blade to balance it.

I had to take out quite a bit more material than I had anticipated, but it hangs flat in every orientation. Trying to be scientific in less than controllable circumstances is a challenge!

   I'll let you know how it mows!

1love

Andy