You have now seen the first series of spot welds necessary to put the strengthening plats in and putting then together. With this accomplished it is time to do the first machining op on the receiver. This operation cuts out the trigger opening and also the holes necessary to weld in the front barrel support. The magazine housing area is also machined out to the rough shape necessary to install it.
This video is showing the machining of the VG1-5 lower receiver op 1′
this is a picture of the part after machining but still in the fixture.