How I Tap Straight Holes for Rolling Ball Sculpture Mechanisms

This is a simple tool for tapping straight, accurate threads into drilled holes. One of the problems with tapping by hand is keeping the tap perfectly aligned so the threads don’t start at an angle. This is another custom tool I got from my late friend and machinist Bill Bethke. I have two of these assemblies; this is the larger one. The base is made from aluminum U-channel, which leaves room for the tap to pass completely through the workpiece. The upright is machined from solid aluminum and has sleeves pressed into it that guide the tap assembly smoothly without binding.

I use this tapping jig when I build chain lifts and helical lifts for my rolling ball sculptures. It allows me to tap the threaded hole for a set screw in the lift adapter. The set screw bears against the flat of a D-shaped shaft, locking the adapter in position so it won’t spin under load. It’s another one of the specialized shop tools that helps me fabricate the mechanical elements that make my rolling ball sculptures work.