Originally Posted by windflower
Every two weeks? I sharpen mine every day, used to carry a spare sharp set too. Sharp blades will allow you to cut faster and use less fuel in the process. Get some kind of grinder with ruby wheels. Maybe a minute per edge. The concave grind may stay sharp longer. The grass will look better, less brown on the cut edge. The blades will only weaken if seriously over heated. Even then they would only dull faster. After three weeks w/o sharpening the trailing edge is probably sharper than the leading edge.
Can someone explain the bold part? When metal gets hot and cools, it becomes harder and brittle (alot more to it than thi, but I digress). That's why on excavator buckets and dozer blades you will see the lines of weld on them. Its called hard facing and resists wear because the weld metal is harder than the base metal (mild steel MIG filler is usually 140,000psi). I took a chunk out of one of my blades. I built it up with the welder and ground it back down. Balanced it and ran it and have not yet seen a difference from one blade to the next.
I know heating heat treated aluminum (6061-T6 is very common) or welding on it will make it soft by "resetting" the heat treatment to a T-0. This is why when welding aluminum fixtures, it common to complete the welds then heat treat.