Editing Printed circuit board milling (section)

==Mechanical system==
The mechanics behind a PCB milling machine are fairly straightforward and have their roots in [[CNC]] milling technology. A PCB milling system is similar to a miniature and highly accurate NC milling table. For [[control theory|machine control]], positioning information and machine control commands are sent from the controlling [[Computer software|software]] via a [[serial port]] or [[parallel port]] connection to the milling machine's on-board controller. The controller is then responsible for driving and monitoring the various positioning components which move the milling head and gantry and control the spindle speed. Spindle speeds can range from 30,000 RPM to 100,000 RPM depending on the milling system, with higher spindle speeds equating to better accuracy. Higher RPM is required as the tool diameter gets smaller.<ref>{{cite web|title=Milling Machine Specifications|url=http://www.lpkfusa.com/protomat/s-series.htm|publisher=LPKF Laser & Electronics}}</ref>  Typically this drive system comprises non-monitored [[stepper motor]]s for the X/Y axis, an on-off non-monitored [[solenoid]], [[pneumatic]] [[piston]] or lead screw for the [[Z-axis]], and a [[Direct current|DC]] [[motor controller|motor control circuit]] for spindle speed, none of which provide positional feedback. More advanced systems provide a monitored stepper motor Z-axis drive for greater control during milling and drilling as well as more advanced RF spindle motor control circuits that provide better control over a wider range of speeds.{{Cn|date=March 2025}}

===X and Y-axis control===
For the X and Y-axis drive systems most PCB milling machines use stepper motors that drive a precision [[jackscrew|lead screw]]. The lead screw is in turn linked to the gantry or milling head by a special precision machined connection assembly. To maintain correct alignment during milling, the gantry or milling head's direction of travel is guided along using [[linear bearing|linear]] or dovetailed bearing(s). Most X/Y drive systems provide user control, via software, of the milling speed, which determines how fast the stepper motors drive their respective axes.{{Cn|date=March 2025}}

===Z-axis control===
Z-axis drive and control are handled in several ways. The first and most common is a simple [[solenoid]] that pushes against a spring. When the solenoid is energized it pushes the milling head down against a spring stop that limits the downward travel. The rate of descent as well as the amount of [[force (physics)|force]] exerted on the spring stop must be manually set by mechanically adjusting the position of the solenoid's plunger.

The second type of Z-axis control is through the use of a [[pneumatic cylinder]] and a software-driven [[gate valve]]. Due to the small cylinder size and the amount of [[air pressure]] used to drive it there is little range of control between the up and down stops. Both the solenoid and pneumatic system cannot position the head anywhere other than the endpoints, and are therefore useful for only simple 'up/down' milling tasks. The final type of Z-axis control uses a stepper motor that allows the milling head to be moved in small accurate steps up or down. Further, the speed of these steps can be adjusted to allow tool bits to be eased into the board material rather than hammered into it. The depth (number of steps required) as well as the downward/upward speed is under user control via the controlling software.

One of the major challenges with milling PCBs is handling variations in flatness. Since conventional etching techniques rely on [[optical mask]]s that sit right on the copper layer they can conform to any slight bends in the material so all features are replicated faithfully.

When milling PCBs however, any minute height variations encountered when milling will cause conical bits to either sink deeper (creating a wider cut) or rise off the surface, leaving an uncut section. Before cutting some systems perform height mapping probes across the board to measure height variations and adjust the Z values in the [[G-code]] beforehand.{{Cn|date=March 2025}}

===Tooling===
PCBs may be machined with conventional [[endmill]]s, conical [[D bit cutter|d-bit cutters]], and spade mills. D-bits and spade mills are cheap and as they have a small point allow the traces to be close together. [[Tool wear#Tool Life Expectancy|Taylor's equation]], Vc T<sup>n</sup> = C, can predict tool life for a given surface speed.<ref>{{Cite journal|last1=Yoon|first1=Hae-Sung|last2=Moon|first2=Jong-Seol|last3=Pham|first3=Minh-Quan|last4=Lee|first4=Gyu-Bong|last5=Ahn|first5=Sung-Hoon|title=Control of machining parameters for energy and cost savings in micro-scale drilling of PCBs|journal=Journal of Cleaner Production|volume=54|pages=41–48|doi=10.1016/j.jclepro.2013.04.028|year=2013}}</ref>