Chapter 2

Magwell and Shallow Top Plane Operations

Time for the infamous magwell operation, well at least the beginning of it. I suppose that this is the feared operation of the entire 0% forging to 100% lower receiver machining process and for good reason too! The reason why I chose to do these operations so early in the game is that the top plane has to be faced off for upper receiver to mate to the lower receiver and to provide for parallel clamping for the remaining operations. Also, in order to face off the top plane of the lower forging, you have to use an end mill perpindicular to the top plane. Since the mini-mill that I'm working on doesn't have the rigidity to face off a full 1" or more at a time I decided to shallow pocket the magwell and FCG well in order to relieve the stress on the cutter. Now with it pocketed the end mill only has to face less than a 1/2" at the thickest part on the top plane. This causes the cutter to deflect less and cut more precisely. Now I can write a CNC program to make that nice 3/4" radius with a 1/4" or 3/8" cutter and get a nice smooth, true radius.

This is only the first operation of the magwell and FCG well - the rest will be machined out in a later chapter.

Here's some pictures of the operations for the magwell:

(sorry about the blurry pic, only one I had of this operation)

 

For this operation I used an 1/8" 135 degress split point aircraft extension drill to do the corners of the magwell. Taking 0.100" pecks for each hole (deepest is around 2.7") the G83 command I used on the CNC was real handy. To let you know how true these holes came out on the underside, look at the last picture and the 2 holes on the left side of the forging that are real close together. On the top there is a 0.014" thick wall between the two holes. On the bottom where they came out the wall measures 0.015". Pretty good in my opinion!

Now for shallow top plane operations I used a 1/4" 2 flute end mill for the shallow magwell and FCG well pockets and an 1/8" 2 flute end mill for the top part of the bolt catch pocket.

Here are some pictures of the shallow top plane operations:

First magwell operation, bolt catch slot operation, and shallow pocketing operation complete! You can see the 100% PWA lower in the background I purchased to take additional dimensions off of and compare first hand to my own machined lower. It really comes in handy when you have the finished product to compare to when you're machining one from scratch!