Here’s an interesting video showing how spindle milling powers (hence forces) can be kept constant if they are properly monitored and used to control feeds and/or speeds in real time. That seems to be the goal of conventional “High Efficiency Machining (HEM)/Adaptive Clearing”. This video shows HEM where forces are monitored but apparently not used for real time control.
It’s a lot easier and less expensive to measure spindle or router cutting power consumption than it is to measure forces. Cutting force can then be easily calculated from that power with this equation: Cutter Force(lbf) = Cutter Power(HP) X 63024 / Cutter Speed(RPM) / Cutter Diameter(in.) / 2. The SPDF Calculator provides inputs for power draw before/after and during the cut so it can calculate the cutting power and force.
The SPDF Calculator supports cutting power calculation from either current measurements for HF Spindles or power measurements form VFD, AC router, or DC spindle/router power supply input power measurements. Although most/all HF Spindle VFDs are supposed to enable monitoring of spindle current some, like Huanyang, apparently don’t. A power meter on the input to the VFD is an alternative approach that is also suitable for measuring and monitoring the AC power inputs for other types of spindles and routers.