A vital part of making good coffee is good grinding blades. If you notice that your blades are getting dull, just replace them. On average normal hardened grinding blades do around 500kg per set. But this can always vary. There are some factors you need to look into:
Do I have a single or 3 phase grinder motor;
What kind of grinding blades do I have, conical burrs or flat burrs;
Is my motor left or right turning, most common is right turning;
Do I want original or after market burrs. Price wise there can be a big difference;
Do I want grinding blades which have a coating, like titanium. This means that the grinding surface is harder which makes them last longer. Not all grinding blades are made with a coating.