Customizable Drill Bit Alignment Jig

While drilling a hole in concrete using a masonry bit, I wanted it to be a perfect right angle to the surface. Seems like I'm always tipping the hand drill a few degrees one way or another. So I created this customizable jig that's meant to be held down to the surface, and the drill bit placed through the middle, so I can tell when drilling that the bit is going in perfectly straight relative to the surface.

The slots in the bottom are meant to be water channels for keeping the drill bit wet while drilling. Also works for diamond-tipped hole saw bits.

It is assumed that the cutting surface of the bit is on the end, and doesn't eat into the plastic while drilling.

OpenSCAD file included for your customizing pleasure, or scale using your Slic3r. Default hole diameter is 9.2mm which is what I happend to need for a 3/8" masonry bit.