Diagnosing Offset Fire Control Group (FCG) Pocket In AR Lowers

Diagnosing Offset FCG Pocket In AR Lowers

There are a few different things that could be causing the issue at hand, so this article will tackle a few of them.  If these do not resolve your issue, feel free to call our technical support line for additional assistance.

1. Clean Tool and Probe Area

a.  You may have debris on a tool. If pieces of aluminum attached to the tool, it could lead to a bad probe. Make sure the tool is clean prior to probing. 

2. Use Compatible Lower

a.  Off-brand lowers could be a potential issue. Due to variation between manufacturers, some lowers may be difficult to fit to jigs, may have features that interfere with probing, or are otherwise not compatible with the cutting code. This is especially true of AR-308 lowers. If your offsets are consistent on a particular brand of lowers, the code can be modified to move the pocket on the X and Y axis.

3.  Proper Tool Installation

a.  The problem you’re facing could be due to an unsecured tool. Make sure the collet is properly seated into the collet nut. The collet should snap into the collet nut when turned at a 45-degree angle. This will ensure that the collet and nut do not come apart. Slide the tool into the collet-nut assembly. Thread the tool-collet-nut assembly onto the spindle. Push the tool all the way into the spindle then tighten the collet nut to ensure that the tool does not walk out while milling. The collet should not be able to fall out of the collet nut once snapped together. 

b.  Here's a video of an ER collet system on a different CNC machine. The video is not of the Ghost Gunner, but the method shown is exactly the same.

4.  Check that the end mill is positioned correctly in the magazine well.

a.  Prior to the Trigger Well Probe operation, the end mill should be centered in the rear magazine well as shown in the following image:

b.  If the end mill is too high or too low, it will contact the ridges on either side of the rear mag well wall, resulting in a forward offset in the fire control group pocket position.  You may need to adjust the X-limit switch position so the t-slot platform homes at the correct height.  

5.  X-Limit Switch

a.  Use the following images to locate and adjust the x limit switch. If the end mill sits low, you need to move the limit switch down. If the tool sits high, adjust up.  

b.  Use the following images to locate and adjust the x limit switch. If the end mill sits low, you need to move the limit switch down. If the tool sits high, adjust up.  

c.  Use the following images to locate and adjust the x limit switch. If the end mill sits low, you need to move the limit switch down. If the tool sits high, adjust up.