J Is for Jig Grinder

Metalworking Glossary for the Letter J

See the index to the Glossaries here:


  • Jacobs Chuck. A common term for the modern drill chuck, it is so named because the original was invented in 1902 by Arthur Irving Jacobs. It was the first drill chuck with a toothed sleeve and key, and after patenting it, A. I. Jacobs founded what would later become The Jacobs Chuck Manufacturing Company. Off-brand chucks built after that design are usually called Jacobs-style chucks and often just Jacobs chucks for short, even though they aren’t built by the Jacobs company.
  • Jeweler’s Mill. Not a traditional milling machine, a jeweler’s mill uses a hardened steel roller to imprint a design into copper or another softer metal.
  • Jig. A device that holds a workpiece in a precise location and guides the tools that cut or otherwise work on it.
  • Jig Grinder. Used almost exclusively by tool and die makers to create jigs (templates used for accuracy in fabrication), as well as dies and fixtures.
  • Jo Block. Another name for a highly precise gauge block, a Jo block is used for making very accurate measurements. The name Jo block is short for a Johansson gauge block, named after its developer, the Swedish inventor Carl Edvard Johansson.