I liked the concept of lindsaytcrawford's remixed drill, but I could not get it to hold the bit well enough to not slip.
I made a collet, that fits within the head to get a better grip on the bit. You will need to modify the file for each size tool you want to use.
Use the files from https://www.thingiverse.com/thing:1798315 and replace the chuck_jaws with this part.
It prints best upside down.