9/7/2014 MAS 863 - David Carr

http://fab.cba.mit.edu/classes/MIT/863.09/people/dcarr/final/final.html 1/5

My final project is a 3-axis CNC milling machine that costs less than $100 (currently $87) to build. It can mill PCBs, wood,and even mild steel.

These PCBs were milled using the machine. The traces are 10-15 mils. The left and lower right boards were milled atapproximately the same speed as the Modela. The upper right board was milled at a speed approximately 50% higher thanthat of the Modella. This possible in part due to the Mantis MTM's increased spindle speed, about 20,000 rpm.

9/7/2014 MAS 863 - David Carr

http://fab.cba.mit.edu/classes/MIT/863.09/people/dcarr/final/final.html 2/5

Some more test pieces: MDO and mild steel with a 1/32 inch mill on the left, wax with a 1/8 mill on the right.

Design

My design was heavily influnced by Johnathan Ward's MTM-AZ, although it shares no common parts with his machine. Ithas a MDO framework that supports an overhead Y,Z zxis gantry above the bed (X axis). All three axes ride on precisionsteel rods and are manipulated by stepper driven lead screws. The working volume is currently 6x4x1.25 inches.

9/7/2014 MAS 863 - David Carr

http://fab.cba.mit.edu/classes/MIT/863.09/people/dcarr/final/final.html 3/5

Machine drawings (DXF) Bill of materials

Brute force stepper driver

The brute force stepper driver is a simple 3 axis stepper driver for use with EMC2. To use it you need a real parallel port(not a USB one). Also beware of parallel ports that only produce 3.3V rather than the full 5V.

9/7/2014 MAS 863 - David Carr

http://fab.cba.mit.edu/classes/MIT/863.09/people/dcarr/final/final.html 4/5

Here are the files for milling the board: Bottom (PNG) Holes (PNG)

Mill the first/bottom layer with a 1/64 inch mill first. Then without touching the board, mill the holes layer with a 1/32 inchmill. Use Z = -.066 for the holes layer and speeds of .5/.5.

Components

MDO frameY,Z axis gantry assemblyBed and X axis assemblySpindle assemblyStepper motor drive boardPC control software

Processes

All of the machine's structure is MDO and is designed to be milled on the ShopBot. The leadscrews and leadscrew nutsrequire drilling and tapping operations that are preferrably perfomed on a lathe. The stepper motor drive board must beassembled and integrated with the control software. The remainder of the assembly tasks are designed to be completed withhand tools.

Schedule

Design prototype (complete) Machine first prototype "kit" (complete) Assemble prototype (completed)

9/7/2014 MAS 863 - David Carr

http://fab.cba.mit.edu/classes/MIT/863.09/people/dcarr/final/final.html 5/5

Revise design (completed) Design control board (complted) Construct control board (completed) Machine next iteration (completed) Assemble next iteration (completed) Integrate control software (completed) Revise design (completed) Present machine (completed)

Over and out.