G Is for Gearhead

Metalworking Glossary for the Letter G

See the index to the Glossaries here:


  • G-code. The most common coding language used with a CNC machine to direct the movement, speed, and other functions of the machine in a specific operation.
  • Gang Drill. A gang drill has several independently driven vertical spindles lined up in a row. It is used for drilling holes in a workpiece consecutively.
  • Gang Milling Machine. A horizontal mill with two or more cutters mounted to its spindle for simultaneous cutting in the same operation.
  • Gang Milling. A type of milling where several cutters are used to machine several surfaces at the same time.
  • Gang-tool Lathe. A gang-tool lathe has a row of tools set up on its cross-slide that can be switched for one another during an operation to perform different functions.
  • Gantry Milling Machine. A large-scale mill with a head mounted on a structure that runs along two rails (a gantry) over a long table. Also called a movable bridge mill.
  • Gas Forge. A forge that is easier to operate than a coal forge, making it ideal for use by a beginning blacksmith. Gas forges generally used propane or natural gas as their fuel source and produce a clean, consistent flame.
  • Gauge. The term gauge can refer to a standard measure for the size or capacity of something, such as the thickness of a sheet of metal. The term can also refer to an instrument used to measure and display the amount of something.
  • Gauge Block. Gauge blocks are precision ground and lapped blocks of metal or ceramic. Each block has a specific thickness and is used for measuring lengths or heights, either individually or stacked with other gauge blocks.
  • Gear Blank. A piece of material to be machined to produce a gear.
  • Gear Grinder. Any machine that is used to machine or finalize a gear, such as a mill, hobbing machine, or a specialized grinder. Gear grinders are also used for removing material from the center of shafts.
  • Geared Head Drill. A geared head drill is a type of drill press that is designed for drilling larger holes than a belt driven machine can. Power is transmitted from the motor to the spindle through spur gearing inside the head.
  • Geared Shaper. A shaper that is named after its type of drive mechanism.
  • Gearhead. A mechanical device used to increase the torque of gears by converting high-speed, low-torque energy into a low-speed, high-torque output. “Gearhead” is also slang for someone who is knowledgeable and enthusiastic about machines and how they work, traditionally referring to those interested in automobiles, but more recently it has also come to refer to those interested in computers and other electronic devices.
  • Gib. A strip of metal or other material inserted between the surfaces of two parts of a machine to take up slack. It will be tapered (slightly wedge-like) so the further it is inserted into the space, the wider it becomes and the snugger it fits.
  • Go/No-Go Gauge. The oddly named go/no-go gauges are inspection devices with dual measurements, one section being a “go” measurement that should fit the finished workpiece, the other being a “no-go” measurement that shouldn’t fit it. A go/no-go gauge is used to test a part to make sure that it is within designated tolerances.  A plug gauge is one type of go/no-go gauge. Plug gauges have two ends, one “go” and the other “no go” and are used by—as the name implies—either plugging or screwing them into a part to test its tolerance. A snap gauge is another type of go/no-go gauge. It has two pairs of jaws, with the first set to the upper limit of the part and the second set to the lower limit. A part machined to the correct tolerance will fit the first but not the second set of jaws. Two pin gauges can also be used in tandem to form a go/no-go gauge.
  • Grain. The individual crystal or unit of the crystalline structure of a metal or alloy.
  • Granite Inspection Table. A common type of surface plate used to check flatness or squareness. Many metalworkers prefer granite inspection tables because they aren’t magnetic, don’t rust, and have non-glaring surfaces.
  • Gray Cast Iron. Often called gray iron, it is a type of cast iron contains flake graphite and produces a gray tinted fracture because of it.
  • Grinding. The use of abrasion to remove material from a workpiece, often as a finishing operation. As a lathe function, it is usually accomplished with the use of a cylindrical grinding attachment mounted to the lathe.
  • Grooving. Cutting or forming a narrow cavity or groove of a certain depth and length in a workpiece.
  • Gullet. In sawing, it refers to the space between two consecutive teeth on a bandsaw blade.
  • Gullet Capacity. In sawing, it refers to the amount of chip that can curl up into a gullet between the teeth on a blade before the chip becomes distorted and no longer is a smooth curl.
  • Gullet Depth. In sawing, it is the distance from the tip of a blade tooth to the bottom of the adjoining gullet.
  • Gun Drilling. A type of drilling process used to produce deep holes in metal a high depth-to-diameter ratios. It makes used of a long, usually thin cutting tool.