Published by Arnot on Mon, 08/29/2011 - 08:02
Correct Clamping of a Lower Receiver
by Arnot Heller III, Detroit Gun Works
In order to produce a part correctly, in production, we as machinists and gun manufacturers have two important requirements. The first is the ability to check the part. It is impossible to make something correctly if the machinist cannot check his work. The second, and the subject of this month’s update, is the ability to hold the part in order to machine it the same time after time.
A lower receiver forging is a difficult part to hold. Ask any fixture builder, and they will shudder at the forge lines and the tapered surfaces. Not only is the fixture tooling important to get right, but also the clamping of the part to prevent bending. It is important that the part be held tightly because of the tight tolerances, and the heavy cuts that need to be machined. The part loses over 80% of its material through the machining process and spends a lot of time getting cut. In addition, there are features in multiple planes that must line up with each other to assure that all the internal parts of the receiver function correctly.
An often overlooked part of the fixture building is the clamping. Many gun manufacturers will get a fixture built and then clamp, not realizing how the placement of the clamps affects the position from one piece to another, or how it might be affecting the piece. If clamped incorrectly the part can actually bend, along its length, causing the top face to have a twist in it when it comes off the machine. This twist is hard to identify, but clearly will cause mating problems with the upper, and positional problems with the pins.
DGW has engineered our fixtures and tooling to not only hold the part for machining, but also to minimize distortion of the lower receiver during the machining process. In addition, everything we do at DGW as gun manufacturers, and our parent company CSP, is automated, providing the least cost of manufacturing to our customers. Every part we make is qualified as a process first, ensuring the best tolerances and throughput by automating our process. You can see more of our automation at www.centralscrewproducts.com. Please call or write with any questions or inquiries.