Machining an AR15 lower receiver

[Highpower]

This is a project that I did at the end of last year, just to see if I could do it – and try to learn a few things about machining along the way. I wanted to give myself a challenge and hopefully end up with a usable part when it was all finished. I made a few minor mistakes along the way, but I learned from them and I am happy for the education that I got while doing it.

You have to start somewhere, so the first thing to do was to find a set of drawings to work from. I managed to find these on the net.


Next was to obtain the raw materials. The 2 forgings are 7075-T6 aluminum which is what the mil-spec called for when these rifles were originally introduced. I also picked up a couple of pieces of 6061 flat stock to use for making fixture plates to hold the forgings while they were being machined.




This is one of the forgings being clamped to the mill table with a fixture plate below it to hold it level and off of the table surface.


After aligning the forging to the table travel with a DTI, and setting a datum point to work from - the first cuts are made to level the deck of the receiver and square up the extension housing lug in the rear. The radius on the lug is also cut, that mates with the upper receiver that holds the barrel and bolt carrier assemblies.


Here the forging is mounted to an angle block and being squared, before edge finding the datum surfaces to locate the next series of cuts to be made.




Drilling and reaming the take-down pin holes that align and hold the upper and lower receiver halves together.