"Anthony" wrote in message
...
"EW" wrote in
:

I'm assuming that new lawn mower blades are sharpened, then hardened
before sold. Question: after sharpening the blades on a bench grinder
(after much use) is it necessary to harden them for longer life, and
if so, how? Thanks.

EW



Mower blades are not hardened to anything appreciable. To do so would
endanger your (and anyone else who happens to be in the vicinity) life or
limbs. My bet is they aren't over 30RC IF that, probably more in the
20's. You want the blade to deform if it hits something, not break.
A localized induction hardening with immediate quinch might work on the
actual edge, but that still leaves the possibility that the blade would
shatter if it hits something, since a crack will form in the hardened
area, which may well propagate to the rest of the blade.
In a nutshell, leave it soft!

It also assumes there's enough carbon in the steel to induction-harden.
Maybe, but it's probably a medium-carbon steel that may not harden very much
anyway.

Maybe I'll do a test on an old blade this summer. I have one that's on its
last legs and which could be sacrificed.

--
Ed Huntress