The Challenge: Design a low cost circuit board milling machine optimized to be mass-produced.
Technical Approach: Several observations on the process of circuit board milling serve as the premise of the design:
Selected Design Features: The overall device has a working area of 4" x 6" with a footprint roughly the size of a letter-sized sheet of paper. Capstan drives were chosen for their simplicity and low cost, and also serve as torque limiters to prevent excessive loads on the small-diameter drive cables. The X and Y axis motion components - such as the motors, capstans, gearboxes, and bearings - are fully integrated into aluminum box extrusion housings. Proper kinematic constraint is used wherever possible to reduce frictional forces and ease assembly. Sheet metal has been utilized to reduce material cost and manufacturing effort. Several of the precision guide shafts double as structural reinforcements for the sheet-metal frame to prevent deflection under the tension of the capstan drive cable.
|One pinned and one sliding shaft mostly avoid mechanical overconstraint.||The Z-axis is exactly constrained thru the use of flexures.|
|The drive mechanisms are integrated into the box extrusion housings.||A preload spring keeps the Z-axis in contact with its leadscrew (a socket head cap screw).|
|I continued this project after graduation. This simple USB-controlled stepper motor driver was intended to decouple machine development from networked control system development.||One of the first milestones was drawing a PCB with a pen.|
|A PCB is finally milled!||Cut quality is revealed through the lens of a microscope. I was debugging why some traces were thicker than others.|
|My senior thesis explains the project in much greater detail. Click to download (PDF).||A classmate named Will Bosworth and I worked together to produce two additional machines, which we brought to Maker Faire 2009 in San Mateo, CA.|
|Mr. Red at Maker Faire.||Mr. Yellow at Maker Faire.|