A simple template to add more holes for shelfs in your IKEA-Billy. Probably also useable for other IKEA-cases and cabinets. The (center to center) distance between the guiding pins and holes is 32 mm. The diameter of the pins is 5 mm.
There is an instant-drill-version and a mark-first-version.
If you want a shelf between predrilled holes, use the drill16
or mark16 version.
If you need other measurements, use the customizable version of this thing: https://www.thingiverse.com/thing:3541489
Happy templating :)