The Mighty Spindle™

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

The Mighty Spindle™

Precision Engineering Research GroupMassachusetts Institute of Technology, Mechanical Engineering Department

Phone: (617) 253-1953Fax: (617) 258-6427

http://pergatory.mit.edu/

Room 3-47077 Massachusetts Ave.Cambridge, MA 02139

By: Roger Cortesi rcortesi@mit.edu http://pergatory.mit.edu/rcortesi/

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

The Mighty Spindle™

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Mighty Spindle™ Design Goals

• Low Cost• High Stiffness• 10,000 to 15,000 RPM• Automatic Tool Changer Option• New Features

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

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

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Mighty Spindle™ Components

GE/Fanuc Motor

Porous GraphiteAir Bushing

Spindle Sensor

Duplex Nose BearingsNo. 30 TaperTool Holder

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

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.

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

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.

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Assembly Steps

Core AssemblyHousing andStator Assembly

Tail SupportAssembly

Drawbar

End Cap Nose Cap

Tool Holder

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.

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Tail Support

End CapTail SupportAssembly

Air Bushing

KinematicGrooves

O-Ring

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Front Air Seal

Labyrinth Seal is integral to the Nose Cap and Shaft

Seal Air In

Nose Bearing

Air ExitSpindle Shaft

Tool Holder

Nose Cap

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

The Hot Swappable SpindleSmall High Speed SpindleHeavy Duty Low Speed Spindle

KinematicAlignment

Grooves

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

The Hot Swappable Spindle

• No need to recalibrate machine after swap• Kinematic interface is repeatable to sub microns

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Cooling the Mighty Spindle

Helical Cooling Groove

Cooling Water In

Cooling Water Out

AluminumHousing

Jacket

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

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

Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

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