Accuracy and normality of tack and datum holes is critical to the manufacturing of aerospace assemblies. These features are frequently referenced for secondary manual and automated processes, and any mis-locations will be propagated further, potentially leading to costly rework. Conventional manual back drilling from pilot holes located in internal features does not ensure normality with the outer skin, and in some cases drill access from within the structure is restricted. The ability to reference internal datum holes from the outside with proper normality helps increase quality by reducing mis-located primary features. To accomplish this, a lightweight manually-deployed 3-axis tack driller was developed. This machine attaches to the outer skin and uses magnetic through-skin sensing technology to accurately locate and drill the tack locations while maintaining normality. This paper will discuss the function and accuracy of this machine in a production setting.