Pocket.TAP Instructions - ghostguns/80lower GitHub Wiki

When orienting the an [80% lower receiver] (https://www.ghostguns.com/search?tag=lowers) to mill out the fire control group pocket using the POCKET.TAP program, make sure that the buffer (rear) of the lower is on the LEFT, and the magazine well is on the right. The 80% lower should be upright with the magazine release button facing you. Use this orientation to set the X, Y and Z values. It is highly recommended that you make or purchase a fixture to use with this program to ensure the part is flat on all planes and parallel to the spindle head and vice. Using a vice alone is not recommended because it can lead to parts that have crooked pockets, un‐even features, and misplaced holes. Make sure the 3/8 end mill is sticking out of collet at least 2” to ensure that the bottom of the tool holder clears the top of the receiver (buffer tube section)

In order to find the X zero position use an edge finder and locate the (left) edge of the bolt catch slot when looking at the lower from the top. When you have the center of your edge finder on the edge, zero out your X value.

The Y zero location is a little more complex to find. The POCKET.TAP program uses the center of the fire control pocket (when looking at the lower from the top) between each wall. The most accurate way to find the center is to first locate one edge (one of the yellow cross‐hairs) with your edge finder, then temporarily zero your Y value, then move your edge finder to the other edge (the other yellow cross‐hair). Pay attention to the value traveled in Y, then move back half that value to end up in the center. Now that you’re in the center – re‐zero your Y.

The Z zero location is at the top of the fire control group pocket. Remove your edge finder and load the 3/8 2‐flute end mill. Bring the tool down slowly until it is within +/‐ .002” from the top of the part. Zero out your Z value.Note: The 3/8 end mill will machine out a pocket right next to the buffer tube hole. On an AR15 paperweight the bottom of the tool holder needs to clear the very top of the lower. Make sure your 3/8 2‐flute end mill is sticking out of the toolholder enough for it to clear the top of the lower. See Step 1 for the exact length the end mill needs to stick out of the tool holder.