Look closely at the leading edge of a tip for signs it is dull. Focus exactly where the top meets the face. If the line of intersection reflects light, you are looking at a flattened area, or wear. Dullness is shiny but sharpness is dark. If you can see a line, that's a sign that the cutting edge is worn enough.
Circulate bits so enough sharp ones are always ready to use while the dullest ones are out of commission. Encourage employees to curtail the use of dull blades and set them aside. A methodical plan saves in the long term. This way you can recycle and save money, too. Timing is the key to making it pay off for you. If you delay maintenance, inefficiency along with quality control issues may ultimately add to the cost of production. Evaluate how long it takes to switch bits so you've got a realistic idea.