Question:- How long should a blade last?
Answer:- How long is a piece of string?
PLOTTER BLADE LIFE IS IMPOSSIBLE TO PREDICT
Only a fool would try - if somebody does - ask them for next week’s lottery numbers.
THE LIFE OF A BLADE IS AFFECTED BY NUMEROUS FACTORS
Very few of these factors are in the control of the manufacturer - almost all are in the control of the user.
High quality blades should last longer than inferior junk but users have much more control over the life (or demise) of a blade than the manufacturer.
BLADES ARE FRAGILE
Far too many are accidentally damaged long before they would wear out.
Without a microscope users cannot see the difference and assume they are worn out - See: Blade Care
A more appropriate question would be:
When should a blade be changed?
YOU COULD CHANGE IT WHEN YOU CANNOT MAKE IT CUT
But that would rarely occur because most modern plotters have sufficient force to cut with a rusty nail - albeit badly - and long before a blade would fail to cut it would be cutting horribly.
SO WHEN SHOULD IT BE CHANGED?
When the QUALITY of the cut is no longer acceptable for the type of work you do.
AND WHEN WILL THAT BE?
Only you can decide. (your eyes will tell you)