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The Mighty Spindle™

Room 3-470 77 Massachusetts Ave. Cambridge, MA 02139. Phone: (617) 253-1953 Fax: (617) 258-6427 http://pergatory.mit.edu/. The Mighty Spindle™. By: Roger Cortesi rcortesi@mit.edu http://pergatory.mit.edu/rcortesi/. Precision Engineering Research Group

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The Mighty Spindle™

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  1. Room 3-470 77 Massachusetts Ave. Cambridge, MA 02139 Phone: (617) 253-1953 Fax: (617) 258-6427 http://pergatory.mit.edu/ The Mighty Spindle™ By: Roger Cortesi rcortesi@mit.edu http://pergatory.mit.edu/rcortesi/ Precision Engineering Research Group Massachusetts Institute of Technology, Mechanical Engineering Department

  2. The Mighty Spindle™

  3. Mighty Spindle™ Design Goals • Low Cost • High Stiffness • 10,000 to 15,000 RPM • Automatic Tool Changer Option • New Features

  4. Mighty Spindle™ Parameters • 1.5 to 2.2 kW • Max Speed of 15,000 RPM • Radial Stiffness at Nose of 87 N/micron • Critical Speed of 23,000 RPM

  5. Mighty Spindle™ Components No. 30 Taper Tool Holder Porous Graphite Air Bushing Duplex Nose Bearings Spindle Sensor GE/Fanuc Motor

  6. Why A Air Bushing in the Tail? • Thermally Forgiving: Allows thermal expansion of spindle shaft. • No Additional Seal Needed: The air flow provides a positive pressure air seal.

  7. The Tail Support Assembly • The Bushing is replicated in place to ensure good shaft alignment. • The Tail Assembly is Kinematically aligned to housing. Allowing it to be removed for service and replaced WITHOUT messing up the alignment.

  8. Assembly Steps Tail Support Assembly Core Assembly Tool Holder Drawbar Housing and Stator Assembly Nose Cap End Cap After the Core is inserted an Nose Cap screwed in the Tail Assembly (w/ Bushing Loose) is mated. The Bushing is pressurized and replicated in place. Ensuring good shaft alignment.

  9. Tail Support Tail Support Assembly Kinematic Grooves O-Ring End Cap Air Bushing

  10. Front Air Seal Seal Air In Nose Cap Nose Bearing Tool Holder Air Exit Spindle Shaft Labyrinth Seal is integral to the Nose Cap and Shaft

  11. The Hot Swappable Spindle Heavy Duty Low Speed Spindle Small High Speed Spindle Kinematic Alignment Grooves

  12. The Hot Swappable Spindle • No need to recalibrate machine after swap • Kinematic interface is repeatable to sub microns

  13. Cooling the Mighty Spindle Cooling Water In Jacket Cooling Water Out Aluminum Housing Helical Cooling Groove

  14. Cooling the Mighty Spindle • Small Cross Section Groove = Better Heat Transfer • Coolant enters at tail to pre-warm it before Nose Bearing Section • Volume Flow Rate of 3 Gal per Hour • No Closed Loop Chiller Needed • Faucet to Drain

  15. The Thermal Model • The Dominant Thermal resistance is: • The contact resistance between the motor/bearings and the housing • The convection resistance between the groove walls and coolant • To Dissipate 200 Watts of Heat: • Tap Water at 10 C • 3 Gallons per Hour

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