Reinventing the Boring Head for Small Mills

Need a really perfect round hole in metal? Grab a boring head! But there is a catch: small machines, like the mini mills so popular with hobbyists, make the boring process pretty unpleasant. That’s why Francis of the Project Havoc YouTube channel designed and built a boring head tailored to small vertical mills.

The problem with running a boring head on a small mill isn’t the lack of motor torque. And surprisingly, it isn’t really a rigidity issue either. Boring heads are single-point cutting tools, kind of like inverted lathes, and don’t require much power or rigidity to work well. The problem is that the typical boring head design is heavy and eccentric, which creates serious wobble in small machines that lack heft. Those boring heads also aren’t very convenient to adjust and take up a lot of Z axis space.

Francis attempted to solve all three of those problems. His boring head design eliminates wobble with a counterweight that automatically adjusts to maintain balance. It is also easy to adjust with a hand-turned leadscrew mechanism. And finally, it is compact and fits on mills that don’t have much room between the spindle and table.

The downside to this design is that it is very complicated and requires a lot of parts. Francis modeled those parts in CAD, then machined them on his vertical mill and lathe. If you like watching machining content, this video is worth the click for that sweet, sweet chip-spitting alone.

Aside from the handful of expected mistakes, the build went well and Francis was able to assemble his boring head for testing. Sadly, the results weren’t great. The boring head works, but inconsistent deviations mean it isn’t up to machinist standards.

Though the video ends on a somewhat somber note, I think the design is promising. Francis isn’t quite sure what the issue is, but I suspect it is a combination of the long boring tool levering against the leadscrew mechanism and the sheer number of parts. If Francis can refine the design and make it robust enough to maintain good tolerances, it should appeal to hobbyist machinists.