On Thu, 16 Jan 2014 08:31:47 +0000, Chris Hogg wrote:

Dunno about mulching blades or bowed sections, but with a rotary
mower, it's the end 2" or so of blade that does the cutting, not the
whole length.

Yep.

My rotary only has that part of the blade sharp. The end of the blade is
the part that's moving fastest; towards the centre the blade probably
just pushes the grass aside.

Not even that the grass has been cut. I had a quick google and found
images of mulching blades that had the sharpened edge going from the
blade tip along the edge up onto and along the hump. Bet I can't find
that image again...

Oh I can, in this
artcle:

http://www.familyhandyman.com/automo...ir/lawn-mower-
blade-sharpening

http://tinyurl.com/lwt3puw

--
Cheers
Dave.