I haven't tried it yet, I am building drill press and in the meantime, I have decided to build a little tool to make drilling of perpendicular holes easier.

Parts required frame:
M6 threaded rods
7.7-8mm metal rods as rails
A few M6 nuts

Carriage with clamps for Silverline rotary tool:
M4 bolts 25mm x 5
M6 bolt 25mm x 1
M6 bolt 40mm x 1
A few M6 nuts

You can redesign clamps to fit your drill/rotary tool.

I am not sure how it assembles, but when I tried the same concept for my pillar drill - drill press. It worked like a charm.

In the photos you can see the version with arack on the back of carriage - that's a version of it for pillar drill.

I want to make a set of helpers for drilling that can have its parts easily swapped.