Hinged PCB Scriber
Hinged PCB Scriber file:///home/nmeronek/myboards/pictures/HingedPCBScriber_FinalMounted.JPG
Overview The Hinged PCB Scriber is a tool used to mark traces directly on a PCB. Designed for the prusa mendel, the tool 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. The tool can also mark drill locations. The hinge design has very little play and can produce .5mm spacing SMD layouts using the scratch and etch method.
Breakdown
file:///home/nmeronek/myboards/pictures/HingedPCBScriber_Final.JPG
The top mounting plate is a heavy washer with mounting holes drilled to match the printer. A piece of one inch flat stock combined with a slice of one inch schedule 40 black steel pipe form the hinge support bracket. A small screw inserted in a nylon bolt serves as both an arm stop adjuster and a Z axis switch for telling the printer when the tool has touched the PCB. The hinge consists of a 3/8 inch nut with holes drilled through both sides and tapered screws pushed into each side of the nut. The arm should be parallel to the PCB when resting on the stop. Gravity is the only pressure holding the arm to the work surface so the hinge should be as tight as possible while still allowing gravity to move the arm. The pen and pin holder are made of 3/4 inch flat stock sit at the end of the arm. The pin is inserted through a slit in the shaft 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 changing the allignment of the pin. Fully tightening an empty pen holder keeps it from falling on your work during pin scribing. Holes are marked by setting the pin down on the hole location and lifting it back up. Because this is not enough to mark the hole correctly, a small DC motor with an offset weight is added to the end of the tool. The motor is only used for marking holes with the pin. You can use a resistor block to control the speed of the motor which should only run fast enough to correctly mark the holes. This 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 level as zero. The z-work level should be a negative number while z-safe should be a positive number.
