Sizing Motors Based on Cutting Forces


Hi Bob,

I missed your question week but glad you have this ‘questionx’ section.  My question is about HSM and how the CAM program moves the cutter into the work.  Does HSM paths cut while accelerating the cutter at the same time or does it typically use ‘rapids’ to accelerate and then cut with constant velocity/feedrate?  I ask this question because I’m working on sizing motors and not sure if I need to account for cutting force when calculating torque due to acceleration or just use that when determining uniform motion torque.



PS.  another question … some speeds and feeds calculators show the resultant tangential cutting force.  I’m assuming this force is correct to use as an external load when sizing motors for the axis and estimating machine stiffness required?  If so, this may be a useful output from gwizard for diy’s.

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Best Answer

Rob, a lot of people want to look at the motor sizing problem from a cutting force perspective, but it’s not the right approach.  The cutting forces (which you can roughly estimate by converting the HP required in the cut to force) are not the most significant influence.  It turns out that most of the force requirement comes from the need to quickly accelerate the axis to the commanded speed.

If you designed a machine purely on the basis of cutting force, it’s acceleration would be so anemic that it would hardly ever reach the speeds you command and you wouldn’t be very happy with it.

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