The thermal properties of the spindle are good but can still be improved by a more accurate temperature control of the cooling fluid. The dynamic behaviour (stiffness) of the spindle is better than specified. The runout of the spindle is so good that electro magnetic noise prevents us from stating an accurate value. The only drawback is the seizure of the spindle at Philips, so limiting the maximum speed to 90,000 rpm is advised. The grinding results of the prototype spindle were already excellent. The redesigned spindle is expected to produce at least similar results with a far more user friendly design.
The properties of our spindle are summarised below.
Maximum rotating speed - 90,000 rpm
Radial stiffness at cutting edge - > 30 N/um
Axial stiffness at cutting edge (calculated) - 60 N/um
Error motion asynchr. + synchr. - 120 um Thermal drift at 70,000 rpm with 0.7 K coolant temperature variations - axial - 0.8 um
Thermal drift at 70,000 rpm with 0.7 K coolant temperature variations - vertical - 0.4 um
Thermal drift at 70,000 rpm with 0.7 K coolant temperature variations - horizontal - 0.3 um
Thermal time constant - approximately 10 sec
Grinding performance - very good
MK43 0AL Cranfield