I've made tons of homemade tools. Lots for the hovercrafts that my dad and I built over the years. Plus I'm an industrial mechanic so I've made plenty of SST (special service tools)
Here is one from a hovercraft project, I just stumbled on this video on my computer.
The summer after I graduated Highschool (2003) I designed and built a 1/2 scale RC hovercraft, 6' long 5hp garden tiller engine, 30" foam prop I designed and built, etc........
Anyways I've been into wood turning for a long time so I figured why not make a lathe to turn a thrust duct for the hovercraft. I cut 2 30.25" disks with a home made router circle cutter, spaced them apart with 2x4's and had a 1" hole drilled through the center. Then wrapped the disks with 1/8" plywood for the liner of the duct and then wrapped I think 2" foam around that. I then mounted a 1" dowel cantilever style to the work bench. Next I made a treadle lathe and used that to spin the duct and used some drywall sanding screen to turn it down into an airfoil shape. (sanding screen works great for sanding foam btw)
Anyway here is a quick video of it.
And a couple finished pictures of the rc hover, I designed and build pretty much everything but the engine, pulleys and belt.