Hinged PCB Scriber
The Hinged PCB Scriber is a tool used to mark traces directly on a PCB. Designed for the Prusa Mendel, it supports two processes for PCB layout. A pen holder for drawing traces and a pin holder for scratching isolation lines. Changes in material height are adjusted using a hinged arm. A DC motor with an offset weight helps mark the drill points by vibrating the pin on the material. Using this tool with the Scratch n' Etch method has produced .5mm pitch traces.
The top mounting plate is a heavy washer with mounting holes drilled to match the printer. A piece of flat stock combined with a slice of black steel pipe form the hinge support bracket. A small screw inserted in a nylon bolt serves as both an adjustable arm stop and a z-axis switch. The hinge consists of a nut with holes drilled through both sides. A screw pushed into each side of the nut completes the pivot point. The arm should be parallel to the PCB when resting on the stop.
The pen and pin holder sit at the end of the arm. The pin is inserted through a slit in the arm and clamped between two nuts. The pin should be perpendicular to the PCB in all directions and as short as possible to keep it rigid. Final alignment of the pin is done with a needle nose pliers after the tool is mounted to the printer. Once the pin is locked in place, the pen holder can be adjusted without affecting the pin alignment. Fully tightening an empty pen holder keeps it from falling on your work surface during pin scribing.
A DC motor with an offset weight is positioned at the end of the arm to vibrate the pin when marking drill locations. The motor should only be used to mark holes with the pin. You can use a resistor block to control the speed of the motor which should only run fast enough to adequately mark the holes.
This tool design requires no modifications to the printer firmware other than setting the z-axis switch as normally closed. The motor is operated using the heated bed connector and gcode commands. The z-axis switch is used to set the board surface as zero.