Eagle PCB -> LPKF Milling Machine Mini-How-To

Instructions for users in EEE, University of Nottingham

EAGLE 4.09rl (Linux) CircuitCAM 3.0 (99) and BoardMaster 3.0 (45)

Steve D. Sharples

Random link: Communicating with VXI11 Ethernet Devices from Linux (How to talk to your Agilent or Tektronix Scope from Linux over LAN)
Random link: Linux Drivers for Agilent Infiniium Oscilloscopes (built on the VXI-11 protocol and user library)

This is the long version, explaining everything step-by-step. If you've followed the procedure before and just want a quick reminder, please go to the Brief EAGLE Export Page.


1a. Design rules

The Eagle software comes with a set of default physical design rules... such as how close together tracks may be, how close the copper layer can be to the edge of the board etc. Unfortunately, these are just a little bit too good for the milling machine within the School, so a set of design rules suitable for in-house board-making has been designed. It is important that the "in-house" design rules are used, rather than the "standard" rules, otherwise your circuit may not be milled correctly. In practice, this means (for each project that you work on) before you do any routing (especially autorouting) the following steps must be taken:

1b. Extra layers (for the milling machine)

As explained above, milling a PCB is a slightly different process to the normal process of making a PCB. in particular: Because of these differences and extra choices, it is necessary in your design to use special layers on your board layout if you want to:
It is important to follow the following conventions, otherwise your boards may not be exported and manufactured correctly

Layer conventions used
LayerNameColourThere by default?Used for...
41tRestrictDiagonal red stripesYesAreas on Top layer that you wish to be completely milled out except for tracks, pads and vias
42bRestrictDiagonal blue stripesYesAreas on Bottom layer that you wish to be completely milled out except for tracks, pads and vias
117tTextUsually whiteNoFor text on Top layer... will be milled out with 0.2mm cutter
118bTextUsually whiteNoFor text on Bottom layer... will be milled out with 0.2mm cutter

Please note the following, which will affect the results given by any Design Rule check:

1c. Shared files in Eagle: /home/share/eagle/

We have set up a system whereby circuits, component libraries, script files (used to perform useful repetetive tasks) developed by one person can be shared amongst everyone else. It involves the use of a shared directory which is located at /home/share/eagle/. Within this are sub-directories...


You'd think that everyone would use the same kind of file standard, wouldn't you? Well, they kind of do, and they kind of don't. Each PCB design package uses its own file standard, which contains much more informations about the design than just physically where the tracks are laid... since different design packages are capable of different things, this makes sense. Once you have finalised your design process, you just want to tell the board manufacturer where to drill the holes and place the copper. For this you use Excellon drill files and Gerber files.

All board manufacturers accept these file formats, and they should adher to a strict standard. What they do with them and how they process them is down to the individual board maker. In the case of boards made in EEE using the milling machine, the Gerber and Excellon files are imported into a program called CircuitCam which will then produce files that consist of routes for the milling machine to mill out (to isolate tracks), places to drill holes, drill sizes etc. Yet another file standard... anyway, it's probably worth looking at the following picture:

diagram of program/file structures

Make sense yet? Lots of different stages, involving 2 or 3 different programs on 2 operating systems. You'll be fine....


The following GERBER files will have been created (assuming your design is called "design"): As you can see, there is one Gerber file per layer. The following Excellon drill files will have been created: These are the files you need to import into CircuitCAM (or give to the technicians on the 9th floor to process). So you'll be wanting to put them on a floppy disc....


4a. The Gerber Files (Top, Bottom and BoardOutline etc)

4b. The Excellon Drill Data



The aim of this bit is to create a "Cut-out" around the outside of the board outline. A large, 2mm diameter milling bit will mill around your board, to make it the correct size. You first need to run the "contour router," by telling which layer contains the Board Outline. It is, unsurprisingly, the "BoardOutline" layer...: You now need to put some gaps in the large gray rectangle, so that the milling machine does not mill out your board completely (it can't do this, otherwise it would fly off the milling machine)...: We now need to ERASE the BoardOutline layer. (If we don't do this, the milling machine will attempt to mill out this layer.)


The 9th-floor workshop technicians need either the "design.cam" or the "design.LMD" files... the design.cam file is larger (so may not fit on a floppy disc) but it does allow them to check the design in CircuitCAM. The .LMD file can only be checked in BoardMaster.


Any comments, or even if you read this Mini-How-To and actually use it, please mail me (remove the no.spams). Also mail me if I've failed to reference a source of knowledge for anything, I'll be happy to correct any omissions.

Feel free to modify, redistribute etc under the terms of the GNU Public License

Hope it's useful!