I'm hoping someone might be able to help me with a guitar fretboard model as shown in the image below. 

I got this far by using a loft extrude between two planes located at either end to create the uncut fretboard  The top of the fretboard has a 10 inch radius and the cuts (.023" W X .070"D) need to follow the surface radius and extend completely from side to side.  The cuts also need to be very accurately placed.   I was able to perfectly extrude the first 5 frets by creating a plane tangent to the radius drawing a center line at the location of the cuts and then sketching a center rectangle from the center line.   I then used a Cut Extrude with the following settings (although the depth was actually .070 in not .2 in)

The problem I'm now having is that as I proceed any further up the neck, SW gives me the error "unable to extrude beyond the edges of the solid surface" or something like that.  I assume it's because, as the side angles are steeper up the neck, the sketched rectangle lays just out side the fretboard edges.  I've also tried it using 4 connected lines and the the relations functions for alignment but I get the same error. 

Other things I've tried are creating the fretboard as a rectangle, doing the cuts and then re-dimensioning the model.   The cuts work fine initially but then the disappear when the model is properly dimensioned .  Also tried creating a plane on either edge of the fretboard and cut extruding plane to plane.  This results in flat cut and not one that follows the top radius as required. 

Any thoughts or help would be greatly appreciated.  I also attached the SW file.

Thanks

Jim