An automated machine tool that cuts away the copper and leaves traces. They can go from gerber files to 2 sided board(3"x5") in a couple of hours ready to solder.
One problem with cnc milling of PCBs, especially with triangular bits is that the pcb material may be warped or of uneven thickness, and more importantly may not me mounted totally flat. This causes traces to be uneven, areas to be not cut at all, and some gouges. It is also imporant to avoid (as much as possible) milling pasted the copper layer as the glass based particles are extremely irritating to the skin and a serious danger in the eyes.
The better pcb routers "test" the grounded board surface by "touching" it over a grid pattern with an electrically connected bit (not spinning) before cutting and then compensate for any viariations as they cut, but those features cost.
Bits used for cutting PCB's should not be triangular since the width of the cut would vary with slight changes in the depth of the cut.
Leveling the work surface can help. Typically, some disposable material such as a slab of MDF is mounted to the table, then the machines cuts the entire upper surface to mill it flat. MDF or other wood bases can warp or swell, so a metal base is ideal, but expensive. The combination of a metal base with a thin layer of wood or plastic is best. Castable urethane is similar to acrylic in hardness, but it doesn't melt like acrylic plastics. ^ It's Much easier to machine than aluminum. It can be replaced...or even resurfaced as urethane sticks to itself quite well. pockets can be made as registration places for repeated alignment of successive copies of a milled board.
Mounting the PCB stock to the work surface can be accomplished by clamps, adhesives, or vacuum.
Clamps are easy to use and commonly available. Unfortunatly, the also restrict the area of the PCB stock which can be milled.
Adhesives are easy to use, and generally very effective. They do require time to set and can be difficult to release. "SuperGlue" works well, sets quickly, and can be released with an application of Acetone (commonly found in nail polish remover) especially if the glue is applied only around the outside of the PCB. For larger stock, some gluing of the board center or areas inside may be needed. In that case, the release agent can be made to reach the glue by means of a channel milled into the work surface prior to the mounting of the stock.
Vacuum holddown is the quickest in operation, and very effective as it tends to hold the stock very flat against the work surface. It does require a vacuum source, connection to the mill platform, and a pattern of chanels or holes must be included in the work surface, with some method of blocking them around the outside of the actual working stock to maintain suction.
Metals and Metal Working / Machineing +
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<A HREF="http://massmind.org/techref/pcbmill.htm"> Printed Circuit Board Milling Machines</A>
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