I have been sharpening big bush hog blades, the smaller blades on my finish mower, and the even smaller blades on the lawn mowers for many, many years.

I have heard several people argue about what to do with knicks in the blade made from stone or sticks.  Personally, I just sharpen the knicks, they look a little like serrated blades when I am done if there are several knicks.

Some people have tried to convert me to their way of sharpening a blade with knicks.  They say to grind the whole blade flat and even, removing the knick, then putting an angled edge back on.  On the largest bush hog blades, that is a lot of metal to remove to both take down the original edge, then angle the edge to factory angle when putting the edge back on. 

I think I am right, nephew believes I am wrong, and removes a lot of steel when helping me sharpen.  I have been sharpening my blades when he is not around to prevent what I feel is excessive wear on my grinding wheels and excesssive steel removed from the blades, as well as a lot of wasted time.

Then again, I had a BIL reply, when I asked him about grinding, "You mean you sharpen the blades?"  I guess he never thought about sharpening bush hog blades, but he only owns 40 acres, so maybe he doesn't have to?