A simple to use drilling-jig for drilling perpendicular/straight holes. You can customize the jig so that it "fold" over the edge of a board (see picture).
The jig is only usable for 1 drill-diameter.

The easiest way to use it: put the jig over your drill, place the drill, put the jig down and flat to the wood without moving the drill point.
The "cross" over the jig is for viewing marks and for the removal of sawdust

Three examples for 8 mm drill are added as STL (the winged versions are intended for 18 mm board).

Remember, it's a guide which will help you, not an assurance that you will drill perpendicular holes :)

For two other types of drill-jigs i made see:
Drillguide for five drillsizes: https://www.thingiverse.com/thing:3014079
Drillguide for all drillsizes: https://www.thingiverse.com/thing:3014111

Look for more tools and the like here:
https://www.thingiverse.com/Coat/collections/coats-toolbox

Happy woodworking :)

Designed in OpenScad

More information about the fantastic and challenging program OpenScad can be found here: https://en.wikibooks.org/wiki/OpenSCAD_User_Manual