Which is the true test of how hard your machine is working ?
If you had to watch the spindle speed meter or the spindle load meter on your CNC machine ... lathe or mill ... to determine if your machine was working too hard, which one would you choose?
The truth of the matter is that although the spindle load meter does tell you the power draw on the spindle motor, the RPM gage is a more accurate representation of how hard the spindle is working. Most machines come with a specific rating for load % per a specific time such as (in laymans terms) : "You can run this machine at 100% for 30 minutes."
That is of course a true statement and you can watch the load meter while cutting and reach that spec. However, if you watch the RPM gage while cutting and see it fluctuate wildly - basically because the motor is trying to keep the spindle at the specified (programmed) RPM - you'll never reach that 30 minute time frame. Because the cutting is so heavy in this type of case, the motor must keep "powering up" to keep the programmed RPM specified. This takes much more power draw on the motor than simply running constant at 100% load for the 30 minutes.
The Solution : When your machine is cutting, watch the RPM gage first to insure that the cutting conditions are resulting in a smooth RPM for the spindle and not wild fluctations as the motor fights to keep the speed constant. Secondly, adjust the cutting conditions so that the load meter is as high as you think you want (there is nothing wrong with 70-75%) and then recheck the RPM gauge to make sure that the RPM's are smooth at those settings. Smooth RPM cutting will result in better life for the spindle motor and smoother surface finish on the workpiece as well.
Happy Chip Making !!
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