Capabilities

The PCB mill is great way to prototype PCBs because it is able to:

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The software for the PCB Mill accpets standard Gerber files for traces and features as well as NC Drill Files for the holes that need to made 

Which Side is Up

If you are making a really simple PCB then you might be tempted to just put all the traces on the "Top" layer of the PCB, however think really hard before you do this. The pads of the component you are going to use will be replicated on both sides of the board (assuming you take into consideration [Dealing with a Copper Clad] Clads --- BUT the traces only connect to 1 of the pads -- specifically the pad on the layer that the traces were drawn on.

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Unlike a PCB order from a normal [PCB house] PCBs on the PCB Mill are made by isolating the desired trace from the plate of copper (known as the "copper clad"). This can cause problems because according to your design there is only a thin trace of copper between any 2 points amongst a sea of essentially nothing (more specifically nothing conductive that would get in the way). With the isolation method that the PCB Mill uses, you have to make sure that your layout program of choice knows that there is copper everywhere else. Otherwise components will 

Dealing with no Plated Through Holes

 In a normal PCB from a PCB House PCBs will have plated through holes. That means that every drill is plated with copper so that the pad on the top is physically and electrically connected to the pad on the bottom. This means that you can run a trace to the top pad or the bottom pad without any consideration. With the PCB milling machine the top and bottom pads ARE NOT connected. So lets say you have a normal through-hole resistor. It needs 2 holes for it to connect correctly, the drill will pass through the top layer of copper then the FR4 fiberglass material between the copper layers and finally through the last layer of copper. The pads are then isolated on either side of the 

Exporting from Eagle CAD

Exporting From OrCad/Cadence/Allegro PCB

Setup

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 Setup Checklist

• Do you have at least an hour to kill?
• Is there a decently fresh aluminum sacrificial board in place
• Is your copper clad sufficiently large
• Does your copper clad have the alignment/holding holes drilled
• Do you have the required tools (drills, end mills, router bits)
• Is the drill usable
• Is the endmill usable
• Are the table vacuum holes drilled into the sacrificial board
  
• Are you feeling lucky enough to use windows XP?

Drill Depth

The easiest way to verify the correct drill depth is to insert the drill into the collet all the way up the collar (the little brightly colored plastic ring that should be on all the drills, should have the drill size marked on the same ring in white). Use the jog function of the mill to move the head so that the drill bit itself is just to the left of the copper clad board but the foot of the head is still squarely on the copper clad. Use your hand (NOT the head down command in the jog window) to gently lower the head until you either reach the bottom of the head stroke or the drill touches the material. If the drill touches the material before the head bottoms out you need to adjust the Up/Down adjustment ring on the head until the drill just barely grazes the aluminum sacrificial board. Now adjust the lower limit of the head so it will go down just a little a more into the sacrificial board. Ideally you want the conical section at the top of the drill head to be fully embedded into the sacrificial board so that only the uniform section of the drill goes through the copper clad. 

Once you believe that you have set the drill depth correctly, jog the drill head to a spare spot on the copper clad, turn on the drill spindle to reasonable speed and then activate the "head down" command in the jog window. Inspect the hole to insure that it has fully and cleanly penetrated the entire copper clad, but has not gone too far (more than 1/4 of the way) into the sacrificial board. 

Go ahead and run through all the drills that you need to do on the entire board. Since the drill bit collars are gaurenteed to all be at the same height, you do not need to readjust the drill depth for every new hole size you have to drill.

If your drill does not have a collar (AKA you got it from ELEC 342 or the likes...grrr....) then you will have to re-adjust the drill depth for every drill that you use (or get the bits from the OEDK).

Mill Depth