H Is for Heat Treatment

Metalworking Glossary for the Letter H

See the index to the Glossaries here:


  • Hacksaw. A metal blade of hardened steel with small, close teeth on one edge. The term hacksaw also refers to the U-shaped frame mounted on a handle that holds such us blade under tension.
  • Hammer. Along with an anvil, the hammer is one of the basic tools of a blacksmith. A variety of handheld hammers are used by blacksmiths in shaping metal, including ball-peen hammers, cross-peen hammers, straight-peen hammers, and sledgehammers. The term hammer can also refer to different powered machines used in forging, like air-lift hammers, drop hammers, and gravity hammers.
  • Hand Forging. A forging made by hand on an anvil or by using a power hammer with dies that are generally flat. Also known as smith forging, flat die forging, or open die forging.
  • Hand Grinder. The predecessor of the bench grinder, having a similar design, but is hand powered instead of using an electric motor.
  • Handwheel. Any adjusting or feeding mechanism shaped like a wheel and operated by hand. Handwheels are used to manually position or feed components on machines like mills and lathes, such as the carriage in the Z-axis or the compound rest in the X-axis of a lathe.
  • Hardening. The process of making a metal harder, whether by quenching and tempering, hammering, or adding alloys to change its chemical makeup.
  • Hardness. How resistant a metal is to indentation or penetration. It is measured by a hardness test, such as Brinell, Rockwell, Scleroscope, or Vickers.
  • Hardy. Any type of tool with a square shank that fits in a hardy hole in an anvil. Examples include a fuller tool—used for drawing out metal and making grooves—and a hot cut hardy that can cut hot metal on the anvil.
  • Head. In milling, the term “head” specifically refers to the upper section of a vertical milling machine, containing the spindle, drive motor and some controls.
  • Headstock. The headstock of a lathe is the powered end of the machine that houses the main spindle and the controls and gears for changing speed.
  • Hearth. A place in a forge where burning fuel can be contained near the tuyere, the opening through which air is supplied to the fire.
  • Heat Treatment. An operation that combines heating and cooling of a metal or alloy in a solid state to produce specific properties in the structure of the material, like making metal more malleable.
  • Heat-resistant Steel. An alloy steel designed for use in applications at elevated temperatures.
  • Height Gauge. Used for vertical measurement, a height gauge has a scale that extends upward from a reference surface, such as a precisely ground base. A vernier height gauge has a sliding vernier scale on the longer main scale. Height gauges can be analog or digital.
  • Helical Gears. Gears that have angled teeth that help them run more smoothly than spur gears.
  • Helix. An advancing spiral path, such as the thread running down the length of a screw.
  • Helix Angle. The angle between a helix and an axial line, such as in helical and worm gears or screws. On an end mill, the helix angle is the angle of the cutting edge of the teeth (flutes) as they wrap around the shaft. The degree of the angle affects speed of cutting, so a lower angle like 35° would cut slower and stronger, while a higher angle like 45° would cut faster and finer. Some end mills will employ variable helix angles with different teeth that help dampen vibrations.
  • Hex. An abbreviated term for anything shaped like a hexagon, such as a hex wrench (or key) or hex bar stock.
  • High-density Cutter. A cutter containing many inserts per inch of diameter. Also known as a fine-pitch cutter.
  • High-speed Steel. Types of alloy tool steel which are designed specifically to maintain extreme hardness when subjected to intense temperatures due to high cutting speeds. Tools made of tool steel can remove metal at a much faster rate than tools made of carbon steel.
  • Hob. A cylindrical tool used to cut gears. The process of cutting gears with a hob is called hobbing.
  • Hobbing Grinder. Another term for a gear grinder.  
  • Hole Drilling EDM Machine. A type of electrical discharge machine that uses a rotating tube as the electrode which sprays a pressurized jet of dielectric fluid as it goes. It is ideal for making holes in materials too hard for standard drilling and is regularly used in the aerospace industry. It can also be used to prep a workpiece so a wire EDM can cut a shape inside of it, where normally it would have to start cutting on the outside and work its way in.
  • Hollow Forging. The process of forging seamless tubes, rings, or other circular hollow parts by expanding or lengthening the hot workpiece over a mandrel. 
  • Honing. A process for finishing ground surfaces to a high degree of accuracy and smoothness, such as honing a knife to make it sharper.
  • Horizontal Milling Machine. A mill with a horizontal spindle that is parallel to the table.
  • Horizontal Shaper. A shaper that is named for the horizontal movement of the ram. The most common configuration of shaper.
  • Horizontal Spindle Surface Grinder. A type of rotary surface grinder that uses the face of its grinding wheel to process the workpiece, usually leaving a very flat, fine, precision ground finish.
  • Hot Roll. A piece of metal that is heated and then rolled under high pressure to reduce its thickness, usually to make it finished size. Hot-rolled steel is identified by a dark oxide scale left on the surface.
  • Hot Trimming. Removing excess metal from a hot part, like a forging.
  • Hot Working. As opposed to cold working or warm forging, hot working is plastically deforming an alloy at a temperature above its recrystallization point to avoid strain hardening, allowing recrystallization to take place simultaneously with the deformation. Hot working is also known as hot forging and hot forming.
  • Hot-die Forging. A process used with difficult-to-forge alloys, where the dies themselves are heated to nearly the forging temperature of the alloy being forged.
  • Hybrid Press Brake. A hydraulic press brake supplemented with electric servo motors is considered a hybrid press brake. While the hydraulic power is utilized to perform bending, the pumping system doesn’t run when the brake is in stand-by mode, saving energy and making the shop environment less noisy.
  • Hydraulic Press Brake. The most common type of press brake currently operating in the market is the hydraulic press brake. Hydraulic brakes make use of a hydraulic system that actuates the ram by transferring fluid under high pressure into one or more cylinders. CNC hydraulic brakes will usually feature two independently controlled cylinders positioned at either side of the ram for very precise movement, allowing both sides to stay parallel to the bottom tooling. They are safer than mechanical press brakes, as they can be stopped instantly while in motion, something not possible with the older flywheel driven brakes.
  • Hydraulic Shaper. A shaper that is driven by hydraulics.
  • Hydro-mechanical Press Brake. A mechanical brake that uses a flywheel to force hydraulic fluid into a cylinder to drive the ram is known as a hydro-mechanical press brake. The hydraulic cylinder provides even tonnage throughout the stroke, unlike traditional mechanical brakes.