This is more of a home "recycled" tool than a home made tool, but a lot of the steps would be much the same.
I start by showing a mangled worn out chuck key which still just about works. I was given an oversize spare chuck key by a friend called Ted (Thanks Ted). This gets machined down using the mill and lathe, into a suitable key for the chuck. Simple stuff, but hopefully entertaining and interesting for some.
I intend to do a quick and dirty job of hardening and tempering the working surfaces, but I didn't show that in the vid.