Spindle torque limits protect the drill from overload. When the torque exceeds the limit, the spindle stops. This prevents the drill from twisting apart under excessive load. I have seen gun drills snap at torque loads just 200 percent above the normal cutting level. A torque limit catches the overload long before that point. Here is how I set up and manage torque limits on my machines for deep hole drilling operations. ...
Tool load monitoring tracks the spindle load during drilling and alerts the operator when the load exceeds a threshold. It catches problems before the drill breaks. In my experience, load monitoring saves more tools than any other preventive measure I have implemented in my shop. I set up the monitoring on the CNC control. The control reads the spindle drive current and compares it to the baseline measured during the first cycle with a fresh tool. I set the alarm threshold at 120% of baseline and the stop threshold at 150%. These numbers are starting points — I adjust them for each material and application. ...