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PCB milling can turn a digital board layout into a prototype by cutting away selected copper from a copper-clad blank. The open-source part of the workflow is best established in the CAM software: FlatCAM can generate isolation-routing toolpaths, but that does not prove a particular open-source CNC mill design is complete, reproducible, or ready to use. You still need to validate the machine, postprocessor, tooling, and setup as one system.
What PCB milling does
Isolation milling removes copper around selected pads and traces, leaving the intended conductive pattern on a copper-clad substrate. The practical chain is board layout, manufacturing-file export, CAM toolpath generation, and CNC motion. The cutter follows paths that isolate copper; it does not add plated holes or automatically create electrical connections between board layers.
For an example of a documented commercial workflow, Bantam Tools’ desktop PCB mill accepts EAGLE board files or Gerber files. That is a machine-specific workflow, not evidence that every CNC router can run the same files or code. Bantam Tools’ PCB milling workflow
How to turn Gerber files into CNC toolpaths
1. Export the board files
Export the copper layers and any other manufacturing layers needed for the board from your PCB-design software. Confirm the units, board outline, coordinate origin, and layer orientation before CAM. A file that looks correct in the layout editor can still be misaligned or mirrored if the export or import settings differ.
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2. Generate isolation paths in CAM
FlatCAM describes itself as “Free and Open-source PCB CAM,” and identifies isolation routing as one of its supported tasks. Its version 8 manual documents isolation-routing options and separate G-code outputs for multiple passes. CAM converts the board geometry into cutter paths; it does not guarantee those paths are safe or compatible with your machine. FlatCAM · FlatCAM version 8 manual
3. Verify the postprocessor and code
Before machining, check that the generated code matches the actual CNC controller and machine configuration. Bantam notes that alternative CAD/CAM software may require a generic or TinyG postprocessor and manual G-code edits for its own mill. For a DIY machine, confirm at least:
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- Postprocessor and controller dialect.
- Units and coordinate origin.
- Spindle start, stop, and speed commands, if applicable.
- Safe Z height and clearance moves.
- Tool-change behavior and any pauses or operator prompts.
Do not assume a G-code file is ready to run because a CAM program exported it. Preview the moves and verify the controller’s behavior using the machine manufacturer’s documentation. Bantam Tools’ notes on alternative CAD/CAM workflows
What bits and board material do you need?
Bantam’s specifications list FR-1 PCB blanks, a PCB engraving bit, and flat end mills for its desktop mill. These are useful examples of the material and cutter categories involved, not universal compatibility recommendations. Match blank size and thickness to the machine, and match cutter geometry and shank to the spindle, collet, CAM setup, and desired trace clearance. Bantam Tools Desktop PCB Milling Machine specifications
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The cutter’s width affects the minimum spacing between features: a wider cutting path removes more copper. Use sharp tools and choose the widest traces your circuit design allows. Smaller cutters may enable finer spacing, but Bantam notes that they take longer on its machines. Actual results on a DIY mill depend on factors such as spindle runout, frame stiffness, workholding, surface variation, feed settings, and tool wear.
What feature sizes are realistic?
Bantam Tools publishes these machine-specific recommendations for minimum trace width and spacing. They are manufacturer recommendations for the named machines, not universal limits or independent performance tests.
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| Machine | Recommended minimum trace width and spacing | Source |
|---|---|---|
| Bantam Tools Desktop PCB Milling Machine | 6 mil (0.006 inch) | Bantam Tools design guidance |
| Othermill Pro | 6 mil (0.006 inch) | Bantam Tools design guidance |
| Othermill | 10 mil (0.010 inch) | Bantam Tools design guidance |
For Bantam’s machines, features below 0.010 inch call for a more precise setup: high-strength double-sided tape, a high-precision collet set, calipers to measure blank thickness, and sharp end mills. Those recommendations are specific to the manufacturer’s workflow; validate equivalent requirements on any homemade CNC rather than treating this setup as a general guarantee. Bantam Tools design guidance
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Plan for double-sided boards and electrical connections
Two-sided milling requires reliable registration between the top and bottom copper patterns. Decide how the blank will be aligned and held for both operations, and verify the chosen method against the machine’s work area and setup. A board that shifts between sides can put vias, pads, and traces out of alignment.
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Milling also does not plate through-holes. Bantam’s design guidance notes that through-hole connections are not plated by milling, so vias need a manually made electrical connection during assembly. Include that assembly work in the design plan rather than expecting the milled board to behave like a professionally plated PCB. Bantam Tools design guidance
How to assess an open-source PCB mill project
Finding open-source CAM software is not the same as finding a reproducible open-source machine. The available references establish a CAM option and a commercial machine workflow; they do not establish a particular DIY mill design with a bill of materials, build instructions, repeatability data, or validated performance. Evaluate any candidate project on its own documentation and results.
- Openness and reproducibility: Are the mechanical design, electronics, firmware, and build instructions available in enough detail to reproduce the machine?
- Feature spacing and repeatability: Are results documented for the actual machine, cutters, material, and setup—not borrowed from another mill?
- Work area and materials: Do the usable travel and bed support the board dimensions and blank thickness you need?
- Software compatibility: Can your layout exports, CAM postprocessor, and controller exchange files and commands reliably?
- Setup demands: How are the blank held, its surface referenced, and any two-sided operations registered?
- Total build and operating costs: Account for machine components, cutters, blanks, and consumables; no comparable cost evidence is established here.
Bantam’s dedicated desktop mill is a commercial reference with published workflow and design guidance, not an open-source machine build. Workflow · Specifications
Safety and machine-specific instructions
Before operating a mill, follow the current manuals for the chosen machine and cutter, especially their instructions on guarding, dust extraction, eye protection, and safe chip handling. The appropriate controls depend on the equipment and material; a general CAM workflow cannot substitute for those instructions. Bantam provides a safety and maintenance documentation index for its products. Bantam Tools safety and maintenance resources
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