What work needs to be done to complete a 8o% receiver?
“....What work needs to be done to complete a 8o% receiver?...”
One obviously needs the uncompleted lower to start with.
Then, one would also need to purchase the proper high quality jig (probably good for 3-4 jobs depending on one’s skill level), the machining bits and a good drill. Then, depending on one’s time and skill level, it can be machined out. I’ve seen some really rough, crude-looking ones that looked like a 5-year old did it, but hey....they worked. IF one had a small milling machine and knew how to skillfully operate it, an 80% can be turned out that looks pretty darn decent. In the end, it’s more expensive than just buying a completed lower, BUT one doesn’t have to go thru the transfer paperwork. However, it’s for PERSONAL USE ONLY. Anything outside of that is either illegal or a real PIA to legally do since one has now become a firearms manufacturer.
Personally, I find it’s just a PITA to do. I’d just purchase a completed lower and be done with it, but it can be done.
The direct answer to your question is about 1/2 way down the page: https://prepperswill.com/how-to-build-an-unregistered-survival-rifle-with-hand-tools/
However, there are a lot of other answers on the link.