RepRap: Blog

@Josef You can make them stronger still by simply setting the perimeter limit to about 200 or so and avoid using infills completely. That's what I do. The only drawback is that you have to calculate the extruder flow rate very carefully. If you get it too high you get the excess sitting on top of the print plane since it has no voids to ooze into. :-)
 

perfect for wishbones that are biased...
 

You could try diagonal holes, to customise the strongest direction.
Also, I find having a fan reduces layer adhesion (though is essential for beautiful prints), perhaps turning the fan off for these reinforcement structures would be good.

In general, more intelligent control over where fan is on/off is needed.
 

If you use horizontal holes with a diameter equal to the layer height you will force SF to do n solid layers over then, and the infill will extend to the next boundary.

You could stagger the horizontal holes and force a fully solid area (apart from those small gaps).

They could stop just short of the outline so they would be covered and invisible.
 

John, if you want to make part stronger (wrt lamination) dip the part into acetone or similar solvent for few seconds and it will make part much stronger.
 

Could the printer pause over a small vertical hole after many layers, with the extruder used to inject material ?

This would form a vertical filament interconnecting a whole set of layers...