Several factors indicate when a CNC tool needs replacing:

l Visual Inspection: Regularly inspect the tool for signs of wear like:

l Flank Wear: Gradual wear on the tool flank surface, reducing cutting efficiency and increasing cutting forces.

l Chipping: Small fractures or breaks on the cutting edge, affecting surface finish and potentially causing dimensional errors.

l Crater Wear: Cratering on the tool face due to high temperatures and pressure, leading to reduced tool life and potential breakage.

l Cutting Performance: Observe changes in cutting performance, such as:

l Increased Cutting Forces: Higher force required to maintain the same cutting speed indicates increased tool wear.

l Poor Surface Finish: Noticeable deterioration in the surface finish of the machined parts can signal tool dullness.

l Dimensional Inaccuracy: Deviations from desired part dimensions might be caused by excessive tool wear.

l In-Process Monitoring: Modern CNC machines with in-process monitoring can provide real-time data on:

l Cutting Forces: Increased force beyond a set threshold can indicate tool wear and trigger an alert for replacement.

l Spindle Vibration: Excessive vibration can be a sign of tool imbalance due to wear or chipping, requiring tool replacement.

By combining visual inspection with cutting performance observations and any available in-process monitoring data, you can make informed decisions about CNC tool replacement. There's no single definitive sign; it's often a combination of these factors.