How much tool wear is acceptable?
On diamond blades, this is simple, the wear is usually uniform and all teeth wear at the same rate.
As soon as the steel body of the tool gets in contact with the rock, the tool should be changed.
Carbide Tipped blades
On carbide blades, the picks may not wear at the same rate.
Always inspect all picks and as soon as the body of any pick is beginning to wear, change the pick.
It is a good idea to keep track of which picks get changed so that any picks that have the tendency to wear faster can possibly be repositioned into a better cutting angle.