On Wed, 05 May 2010 11:03 -0300, "Leonardo Marsaglia" <leonardomarsagli...@gmail.com> wrote: > > I'm trying to understand this because my idea is to mill lobe shapes for > making camshafts, and it would be very nice to make the roughing process > with a mill. >
> > I'm trying to clear my doubts before i start to spend money on servos and > encoders.. > > Thanks again and i hope i've clean about my doubt. > So far the discussion has been all about the technical details of how to control the motor, encoder counts, etc. However, when I look at this application, the first thing I think about is stiffness. A conventional rotary positioning axis uses a worm gear or other mechanical reduction so that large cutting forces applied to the workpiece can be resisted by relatively modest torque from the motor. In addition, the gearbox reduces the inevitable small motor position changes to very very small workpiece position changes. A direct drive spindle motor will have to have enormous torque and very good tuning to achieve the same stiffness. Good PID tuning might be able to reduce the steady state error, but when an individual flute of a spinning end mill applies a brief force to the axis, the axis will move. Only after it moves will there be a position error that the PID can use to drive the axis back to the proper position. Just because a particular motor works well driving the spindle in lathe mode does NOT mean it will be even close to good enough for direct drive positioning. Regards, John Kasunich -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
