Spindle-Load

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. ...

I have broken more gun drills than I care to count. Every one of those breakages happened inside the hole where I could not see it coming. That is what drove me to build a real monitoring strategy — not just watching a spindle load bar on the control, but layering multiple signals so I catch wear, chip packing, and material anomalies before they snap the tool. Here is what I have settled on after years of testing different approaches. ...

Spindle load monitoring uses the spindle drive current to measure the cutting load. Changes in the load indicate changes in the process. The drive amplifier converts the mechanical torque into an electrical current signal. The CNC reads this signal and displays it as a percentage of the drive’s rated capacity. In my experience, this single data stream catches more process problems than any other sensor on the machine. Establishing the Baseline I record the baseline spindle load for each job using a new tool. The baseline is typically 30% to 50% of the spindle drive capacity. I note the load for each stage of the cycle: entry, steady cutting, and exit. Each stage produces a characteristic load signature. ...