First there are three independent jaws 1-2-3, threaded on one side of one end, and ground to angles on the other. They are hardened for long service life — they are literally the hard parts.

By the time your chuck is first assembled the split nut will already be in two pieces. This intentionally broken piece is the ingenious core to Jacobs' design and fulfills the key design requirements: engage with the jaws, engage with the outer, and fit over the central core. The bottom end of the jaws is threaded so that they can advance and retract in unison and the split nut has the mating threads for that motion. To fit around all three jaws, and the body of the chuck, the nut has to be split in half so it can come together around the jaws.

Manufacturing Tip:
Brittle materials will break and keep their shape so they can be put back together and "register", keeping their original relative dimensions intact. This means the threading inside the nut still works, even though the piece was split into two!

Finally, the sleeve presses on to the split nut and holds everything together. The press-fit also means that when the sleeve (on the outside of the chuck) turns, so does the split nut, moving all three jaws simultaneously.

Manufacturing most parts is difficult enough, but making a complicated threaded part, ground to the perfect size for the interference fit, then broken in half is unusual. A better description of the design is creative, there is no other way to assemble the chuck unless the split nut can come apart in two pieces.

Ball Bearings allow the split nut to spin smoothly while tightening or loosening

Jacobs Super Chucks are built with commonly found ball bearings, making replacements easily findable. The bearings usually don't see much wear since the split nut rides on ball bearings only when tightening or loosening. When the chuck and bit are drilling a hole, the balls are stationary in their positions within the chuck- they do not roll.

By most historical accounts, Arthur was not highly educated. But he must have been very observant, and had acquired some experience and knowledge to enable him to make such a creative and useful design. The design skills include machining, threading, geometry, gearing, fits and tapers. Metallurgy is usually used to design parts that do not break and have the correct hardness and other qualities for the mechanism-glad he skipped those classes.

The chuck also embodies a very important design philosophy, elegant and simple is usually hard to achieve, but he did it.

Drawings from Jacobs' original 1902 patent

Jacob's first patented his Super Chuck in 1902. After some very minor improvements he again applied for a patent in 1912. The drawings show the sleeve with a diamond knurl pattern while the many older style Jacobs Super Chucks with straight sleeve splines mechanically identical. Some minor aesthetic changes have occurred over time, but the original (nearly 120-year old) idea from 1902 has proven to be a great one.

To truly experience Jacobs design, we recommend taking the time and disassembling one. It's also a great time to perform some preventative maintenance and give some life and lubrication to an often neglected piece of shop equipment.

Get a service ring and press the sleeve off the arbor with an arbor press. Fully remove the sleeve over a lunch tray and take it all apart. Check out our video of the whole process. Shops are dirty and over time, lack of lubrication coupled with a buildup of sawdust or metal chips can bring your chuck to a halt. All the parts are available to make it new, all of our videos are there to help with the most common repair problems. This is a great project for an apprentice to learn and at the same time improve your shop's productivity and performance.

We've built up a bit of a collection — I think you could say we're fans.