The Modified MiniMill™

A small milling machine with linear motors and air bearing.

By: Roger Cortesi [email protected] http://pergatory.mit.edu/rcortesi/ Precision Engineering Research Group Massachusetts Institute of Technology, Mechanical Engineering Department Room 3-470 77 Massachusetts Ave.

Cambridge, MA 02139 Phone: (617) 253-1953 Fax: (617) 258-6427 http://pergatory.mit.edu/ Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Using the Axtrusion™ as a building block, create a desktop Milling Machine

“I will call it… MiniMill™”

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

MiniMill™ Functional Requirements • A part accuracy of 0.001” (25.4 m m) • A work volume of 300 x 300 x 300 mm • A manufacturing cost of $20,000 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

MiniMill™ Prototype Budget

Materials Air Bearings Linear Encoders Linear Motors Linear Motor Amps CNC Controler Spindle Misc Hardware Aluminum Polymer Concrete

Total

$ 5,922 $ 1,836 $ 3,810 $ 3,000 $ 10,000 $ 4,000 $ 1,500 $ 2,000 $ 6,500

$ 38,568

Assume that the in-production manufacturing cost between 30 and 50% of the prototype cost.

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

MiniMill™ Production Budget

Estimated Material Costs

Production Unit Cost

Air Bearings Linear Encoders Linear Motors Linear Motor Amps CNC Controler Spindle Misc Hardware Aluminum Polymer Concrete

Total

$ 4,145.40

$ 1,285.20

$ 2,667.00

$ 2,100.00

$ 3,000.00

$ 5,600.00

$ 1,050.00

$ 1,400.00

$ 2,400.00

$ 23,647.60

% single

70% 70% 70% 70% 70% 70% 70% Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Some Competing Machines

The Compact DMC™ (left), and the XV Tabletop™ (middle) Machining Centers by Defiance. The Benchman™ Series (right) by Light Machines.

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

Space Efficiency

• Three times the Work Vol / Machine Vol of other small machines • Twice the Work Vol / Floor Space of DMC Compact Center™ • Four times the Work Vol / Floor Space of the Other Machines Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

Some Other Initial Concepts

Sawyer Motor for the X & Y Directions. Traditional or Combined Unit for the Z axis and Spindle Two Axtrusions on the base (X &Y) and an Axtrusion for the Z axis.

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

Two L’s Used to Make Machine

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

MiniMill™, The Final Concept

One Axtrusion on the Base (X) One on the Gantry (Y) and one for the Z This allows for two identical “L”s to make the structure.

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

Final Concept Features

• Only Four (4) Major Parts • “Hot” Swappable Spindle Interface • Auto-Tool Changer Easily Accommodated • More Crash Resilient Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.

The Model Results

(via a MatLab script) Error at the Tool Tip (microns) vs. Tool Position 2 1.5

1 0.5

0 -0.5

-1 -1.5

-2 -150 Upper Limit X axis Y axis -100 Lower Limit -50 0 x & y position in mm 50 Z axis 100 150 Property of Roger Cortesi, MIT Precision Engineering Research Group. DO NOT COPY or TRANSMIT without written permission.