A modified webcam to be able to focust at 30-50 mm it's mounted parallel with the drilling spindle axis. In order to modify the webcam I have pulled out the outmost lens.

In the left side it's the recommended web cam (but you can use whatever do you have at your hand). It's more usefull because the main board has rectangle shape and the mounting it's done using 4 screws in corners. More than that this kind of webcam allows a focus range of 1-2 cm without and changes. It you pull out the outmost lens it will result a smaller working distance.

PCB Design
On the rectangle representing the "Board Outline" will be placed 2 pad's/vias in oposite corners. Those will be used for centering/calibration/scale.
Most important it's the origin. This has to have the coordinates X=0 Y=0 in the generated excellon file.
In the same time the those calibration pad has to be at the minimum and maximum coordinates compared with rest of holes/pads/vias.

Generally electronic design programs are generating the coordinates unmirrored - like are seen from the pcb view (from above of top layer).
That's because the most of boards are made double side and have bare copper on both sides.
In our case most of boards are single side and because of that we have to mirror the coordinates.
My recommendation for those two pads it's to give them a very small drilling diameter in order to have them grouped at the beginning of resulted excellon file.

For example below it's a sample drilling file with alignament pads placed in corners :

Usually the CNC machines are starting from a down left point and are starting to work to positive coordinates -> to right and up.
It's not always like that : you can have the starting point in the upper right corner and negative drilling coordinates. This way the spindle will move to down left positions. Please remember that you always have to make some test before starting to work.

The reference hole must always have coordinates X=0 si Y=0.

This limitation has been introduced in order to simplify the operation mode and to avoid sending more coordinates.
In our example the x1designed and y1designed would have the coordinates X01800Y01850 - we know those from Excellon file and we will fill them in the DrillListConvertor executable.
Coordinates x1found si y1found will be those found at optical inspection with webcam mounted next to drilling spindle.

If you use Target 3001 place the alignamnet pads on left top and right down. After that generate the excellon file mirrored. You will have the alignament holes like in the above example.
If you mirror the coordinates from EDA remember to exclude mirror from DrillListConvertor.

In Eagle palce the pads/vias/holes in left down and right top. Move all the board with the left-down hole over the origin.
In Cam processor choose Excellon as Device and uncheck position coord.
We will mirror the coordinates on Y axis from DrillListConvertor.

In Kicad place the reference "offset adjust for drill and place files" over the left-down pad.
Then choose posprocess>create drill file. At drill tools choose auxiliary axis.

Dependin the EDA suite that you use take care that the reference point must have coordinates X=0 si Y=0.

Further more print the image and produce the board using toner transfer method.

In Mach3 you should copy the following files : - Video.dll in folder c:\mach3\plugins - WmCpyDta.dll in folder c:\mach3 (path c:\mach3 depends on your installation and it is given as example).
2.1 Configuring offset between webcam axis and drilling spindle axis Start the video plugin from Mach3. 1. Start spindle and make a hole in a test position. 2. Push button set X=0 Y=0. 3. Click over Mach3 parent window such way as the back window will be active (blue border) and Video Plugin on top. From cursor key move webcam over the hole from step 1. 4. Push "Save curr coord as Offset". Also this offset could be modified and saved from settings button.

2.2 Measurement of pcb and seding coordinates to DrillListConvertor
1. PCB etched will be placed on machine table.
2. Move the webcam over the reference pad (coordinate X=0 si Y=0 in excellon file).
After fine movements (CTRL+cursor keys with Mach3 window active) Push "Set X=0 Y=0".
3. Move the cam over the oposite corner alignament hole and push "Send Corner Pos" - this will send actual coordinates to DrillListConvertor - and
"Add Offset" - this adds to current coordinates offset value.

Choose source and destination files.
In x1design si y1design fill the coordinates from excellon source file.
Check :
- Mirror X - depending how you have generated the excellon file and how is the pcb placed on machine board
- Scale XY
- Rotate Holes
- Auto Load in Mach3

Push Convert.

IF everithing went well in this moment Mach3 and machine it's prepared to start the work.
Make a simulation, configure Z=0 acordingly and you can drill the board.

Plugin can be donwloaded from address : http://www.dioda.ro/Downloads/get=6.html
Drill List Convertor can be downloaded from address : http://www.dioda.ro/Downloads/get=7.html (Attention it needs .NetFramework 2.0 )

A practial example
[align=left]I have choosed the USBAsp board.
Those are eagle config :