AR Lower Manufacturers Building Fixtures for the AR15 Lower Receiver
Recently Central Screw Products acquired a Zero Point Positioning System (ZPPS). As ar lower manufacturers, the system has turned out to be a very good investment and it has allowed us to build better fixtures and make a better ar15 lower receiver. Below I want to outline how we build a fixture with the Zero Point Positioning System and why we like the system so much.
The most important part about building a fixture when machining is whether the fixture will repeat. It is essential to eliminate variables in the machining operation and by building good fixtures that repeat, it allows us to hold the tolerances we want to hold on the part. The ZPPS really helps us to be able to repeat on fixtures because we machine the fixture on the ZPPS system, and then place it back on when we want to run the part. The system eliminates us having to find the position of the fixture every time we place a new fixture in the machine. Since we have cut all our fixtures on the ZPPS , and we keep our zero in the same spot we know we are within .0002″ (the repeatability of the ZPPS).
It has taken us some time to build a small inventory of fixtures, but now we are able to switch from job to job in under 15 minutes. In addition, we are able to run very small lot sizes of parts because we can switch so quickly from one operation to another. Last week we finished running our first ar15 lower receiver batch, before broach, off our production tooling. We have three operations before broach, and we were able to switch between all the ops quickly and effectively.
This particular fixture is for some operations on our DGW 308 lower receivers. What is neat is that we need to do work on the part in two different locations. With the ZPPS we are able to do that quickly and effectively, without needing a 4th axis. Here are the steps:
1.) Mill all the sides flat on our block. This is important to make sure that all the sides are flat and true to each other. We do this by placing it in a vise that we can attach to our Vero-S.
2.) Spot, Drill, Tap, and helically bore the spots on the block to hold the ZPPS plugs. You can see from the picture that we place ZPPS plugs on two sides, so we will be able to flip the fixture 90 degrees when we are ready. Again we do this in the vise.
3.) Hold the part in the ZPPS and make the entire fixture. By holding the fixture in the ZPPS, we can assure that as long as our machine is true, our features will line up as close as possible to the model we created.
So far we have seen incredible repeatability with this process. It should also be noted that if we make a mistake we can put the fixture right back into the ZPPS and cut, without having to indicate everything in. Over time, these advantages in efficiencies and cost will make us the most competitive amongst ar lower manufacturers.
As always please contact us with any questions or comments. We are always excited to talk about guns and machining of guns!
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