There are three different methods for creating slots in a boards.  Each works best for different scenarios so you will need to opt for the most appropriate.


This is most suitable for small slots, especially when combined with a pad as with tabbed components.   Using the [Pad Styles] tab under design technology, create a new pad style. Immediately underneath 'Hole' is a 'Shape' box which allows you to change the hole from a round drill hole to one of several alternatives.  When choosing these, bear in mind that a mill is a rotary tool which can't produce sharp corners, so all corners will be radiussed by at least the minimum milling tool size.  This is specified on the [NCDrill] setup page.  Where possible, 'Oval' is likely to be the cheapest option to manufacture, simply because it only requires a single pass of the mill whereas all other shapes require profiling with a smaller tool (which takes longer and has a higher proportinate tool wear).  As with any pad style, it's perfectly acceptable to make the pad smaller than the drill hole so as to create a copper-free slot.  When generating plots for any deswign containing slots, milling must be enabled by checking the 'Slots' option on the [Settings] tab for the drill data plot in the plot output dialogue.

Method 2

This is most suitable for creating isolation slots.  Method 1 works for any single slot, but becomes cumbersome when a slot has multiple segments.  To use this technique requires a dedicated layer with no pads or vias.  There's already a layer type which meets this requirement, but it's probably already in use on the outer sides of the board, so on the [Layers] tab under design technology, use the [Add] button to create a new inner layer using the layer type 'Silk Screen'.  You can choose any name for this, but it's probably best to avoid the name 'Routing' because of the potential confusion between routing a slot and routing a track.  The assumption will be that the name 'Milling' has been applied.

After creating appropriate line styles (if necessary) add shapes of the same size as the desired slot width to this layer.  The shapes exactly define material to be removed.  The program has no checks for tracks being interrupted by these shapes, so it's up to you to make sure that no track routes cross these shapes., especially if the design is being autorouted.

When outputting the drill data plot, as well as enabling slots as described above, it's also necessary to set the 'Milling' layer to 'Y' on the [Layers] tab to convert the previously defined shapes to milling commands.

Method 3

This is probably the simplest method to implement, but it's really only suitable for fairly large apertures.  As well as the normal board outline, if a second board outline is nested inside the first, it's treated as a cutout.  More can be added if multiple cutouts are required.  Once again, slots must be enabled in the plotting dialogue, but this time the 'Board' option also will be required.  There is a caveat with this approach.  Because the board profiles become milling instructions, it's the inner edge of the outer profile which defines the edge, and conversely, the outer edge of any inner profile.  This differs slightly from the norm for Gerber plots where the centre line is taken.  If trhe board sizes consequently need to be fine tuned, this is most conveniently done by using the [Shape Information] dockable bar.