"George" wrote in message
...
Meaningless answers to an unanswerable question. They last until they're
too dull to plane the kind of wood you have to plane at the moment. Might
do the next variety well, but that's a horse of a different color.

You bring up a good point though. If you have blades that are getting dull,
but can still cut, replace them now. Save the old set for the first pass or
two of some wood that may be questionable so as not to ruin the good set of
knives.
Ed