Hello john, Thanks for your explaination, i've forgotten to talk about the mechanical situation of the machine.
I've always thought about using a worm gear reduction because it's farther more secure than direct pulley reduction, the only problem with the worm and gear is that the revolutions will be decreased a lot, then i would need a transmission or another motor to use the axis as a spindle drive. This is a little bit complicated since i would like to make the machine the simpler as i can. But may be it would be better to start with a motor reduced by a worm and gear transmission, and think about getting high speeds later... because what i need the most is to mill the lobes, so i don't really need high rpm at the moment but i needed to clear the doubt. So thanks again for your answers :) Regards. Leonardo. 2010/5/5 John Kasunich <jmkasun...@fastmail.fm> > > > 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 > ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
