As a rule of thumb never let your blades get duller than 0.008”  (8/1,000 inches) edge radius.  Certain grades of carbide are able to obtain and keep a sharper tip than others.  See our article on Acheivable Edge Sharpness for saw tips. 

This may not sound that dull but it is like trying to cut with the edge of a paper clip.   A much better figure for maximum allowable dullness is 0.004” which is about the thickness of a piece of paper. 

The rounded tip can be thought of as part of a circle.  The radius of the tip is the radius of that circle.   

The radius is shown by dotted lines A and B.   If the radius is 0.008” then the diameter is 0.016” as shown in the right hand drawing.   0.016” is about the diameter of a common paper clip.

Typical edge radius on new saw blades

Don’t run your blades too long.   The longer you run them the more that has to be ground off to get the saw tips sharp.   See our section on Saw Blade Sharpening.  

If a saw blade should run 10 hours and have 10% wear when it is run twenty hours it will have 30% wear.  All this depends on the materials, machine, saw blade, etc.  But it is always true that dulling is not a linear process.  The duller a tool is the faster it gets even duller.   In addition dull saw blades are much more likely to lose teeth, which is expensive, and much more likely to have shoulders rip off which is really expensive.  

A good shop will help you determine how long to run your tools and will be able to tell you why.