Monitoring Cutting Power and Force

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.


That is a pretty cool concept! I did actually poke into if one could capture spindle load for the Nomad after I saw that was a metric available on Haas machines. Took a drive-by look at the PCB and the motor driver spec sheet and as I recall the driver chip supports current measurement but I couldn’t find the sense resistors (if they exist) required on the controller PCB.

It’s probably a lot easier to monitor the spindle’s power supply AC input if you can with something like this. :wink:

Agreed, definitely the winner for Shapeoko with spindle power coming independent of everything else, but the Nomad AC input is spindle power + axis motors + controller + whatever else may go on which I suspect would rather spoil things. Nomad would probably require a bit more of a boutique solution that sits between the driver board and the spindle motor.

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I think you’ll find that the only thing that varies much is spindle power when cutting. Maybe do an “air cut” to verify that and determine a more accurate non-cutting power draw if necessary? It can be difficult to measure the power input into brushless DC motors unless you have the proper equipment and expertise.

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Agreed on the relative complexity. Its not really the expertise or equipment holding me back - its the time and motivation. Have many projects to work away on - at some point maybe I’ll get to this one.

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It appears that current sense resistors aren’t (weren’t?) used, and that the Overcurrent Protection threshold is (was?) set to 8.8 +/- >20% Amps.

@mikep, @Tshulthise Here’s a 300 Watt water cooled HF spindle with a 0 - 60,000 RPM speed range that might be a nice upgrade for the Nomad. And, using the right VFD with it would enable direct monitoring of current.



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OOPs sorry!

48mm diameter… seems pretty large.