This is a 90-degree, almost fully parametric drill guide created in FreeCad. Edit parameters in the spreadsheet "Parameters" spreadsheet.

The stl provided is for a 3/4" drill bit.

I printed in PETG-GF with multiple shells for strength. (I have granddaughters, in case you're wondering about the pink filament).

I printed in its normal orientation with supports for the observation / chip holes. It might be possible to arch those holes to eliminate the need for supports, but I find tree supports easy enough to use that I didn't bother.

I'm new to FreeCad, so please don't use this as a tutorial.

Power tools can be dangerous! Please don't depend on this piece of non-designed plastic doing anything to keep you safe.