In Process Gauging for Manufacturing AR-15 Lower Receivers, .308 Lower Close to Ready
For those of you who don’t know, the AR-15 Lower Receiver is a finicky part to manufacture. At Detroit Gun Works we start with a forging, and even though we use the highest quality forgings available, the surfaces do not repeat as close as we would like. Therefore we have developed special fixturing to hold and locate the Lower Receivers in each of our operations.
As with any component there are areas of the part that are more important than others to the function of the final assembly. For this post we are going to focus on the top face of the AR-15 Lower Receiver that mates to your corresponding AR15 upper receiver. As gun people we all know that this fit is what separates a nice rifle from a marginal one, and we spend extra time in our process to make sure that this fit is on the money every time.
In order to do this we use a really cool technology called in-process gauging or machine probing. You can see in the second fixture a quick example of the AR-15 lower receiver with pins in the takedown and pivot pin holes. If we set up a line between the two centre points of these holes, that line needs to be parallel and a certain distance from the top face. This distance is the critical portion of the lower that determines that fit you get with your upper. If it’s made terribly the gun won’t even cycle, as this affects the feeding of the bullets from the magazine.
Therefore we use a machine probe like you see in the first picture. The probe we use is made by a company called Renishaw. The probe works in conjunction with our Brother CNC Machining Center’s control. By feeding data through the control we are able to manipulate it using a programming method in G-code called Macro programming.
After we finish manufacturing the takedown and pivot pin holes, along with the top face, we bring the probe in and we find all the surfaces. The probe enters each of the holes and touches the sides in three places, does the math and finds a center point, then we measure along the top face of the lower receiver and set up a line. Through some fancy macro programming we compare the distance between the two lines(along with the fact that they are parallel), and then we do one of two things:
1. If the part is within tolerance we continue through the operation and finish the part. In addition, we make a small adjustment to the tool compensation to make sure that as the tool gradually wears we continue to adjust the distance on the top face. This is the way that we assure conformity of all of our products during unattended operation.
2. If the part is out of tolerance, the tool automatically adjusts and redoes the cut on the top face. We measure the top face again and if it is still of then the machine stops and waits for us to fix it, if it comes back to size then it continues to the next part.
The cool part about the whole operation is that we can verify dimensions during the run. All these areas play together to make a high quality product, including fixturing, tool selection, and speeds and feeds. When we add in-process gauging to our AR-15 lower receiver manufacturing process we can assure that the product we are making conforms to our standards. This extra step enables us to optimize the entire process and make better and better parts.
As always we look forward to your inquiries and your orders. We are continuing to grow, but are more focused than ever on being the best AR15 lower manufacturer in the world. We are also using all our knowledge of the AR-15 lower receiver and putting it into a AR .308 lower receiver.
Our tooling is almost complete and we will run through our final prototypes in the next few weeks. Our .308 lower will be a DPMS style lower receiver milled out of a forging with a solid trigger guard. It is a wicked looking forging and we are super excited about the look. We will be offering it as a standalone lower initially but plan on following very shortly with a matching upper. The .308 upper receiver will be made out of a forging as well, and the lines are absolutely perfect on both of them. They will both have all the final milling done on the same equipment as the AR-15 lowers and we look to use all the same technology to bring you a sweet package for the .308 platform. Thank you for your interest and please contact us with any questions!
Visit http://www.centralscrewproducts.com/detroit-gun-works/ to know experience of gun manufacturers.
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