P Is for Pitch

Metalworking Glossary for the Letter P

See the index to the Glossaries here:

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• Pancake Forging. A quickly and easily created rough forged shape that is usually flat.
• Parallels. A pair of accurately ground hardened steel bars made to an exact size to support work in a precision setup.
• Parting Line. The point where the dies meet on the surface of a forging and flash is formed.
• Parting. A lathe function that cuts off a section or part from the end of an overall workpiece by plunging a blade-like cutting tool all the way to the center of the spinning metal. 
• Pedestal Grinder. Essentially a bench grinder that is mounted on a pedestal to be freestanding in a shop. They are sometimes larger than bench grinders.
• Peripheral Milling. Also called plain milling, it is a milling process in which the outside of the cutting tool removes material from the workpiece. The axis of the cutting tool is parallel to the surface being machined.
• Peripheral Surface Grinder. Another name for a horizontal spindle surface grinder.
• Pickling. The process of using a heated acid bath to removing oxide scale from a forging.
• Pig Iron. A crude, high-carbon iron formed from smelting. It gets its name from the traditional arrangement of the molds used to create ingots. A shape is formed in sand, with the individual ingot molds arranged in a branching structure at right angles to a central channel called a runner. Someone observed that the configuration resembled rows of piglets being nursed by a sow, and the name stuck.
• Pilot. In drilling and similar operations, it is a guide at the end of a tool such as a counterbore to keep it aligned with the hole.
• Pilot Hole. In drilling operations, a pilot hole is a smaller hole drilled prior to the final larger hole. It helps guide the secondary drilling for accuracy and to reduce resistance.
• Pin Gauge. A pin gauge is used to inspect the features of a bored hole, such as straightness. It doesn’t check a measurement so much as whether the hole is within tolerance. Two pin gauges can be used in combination as a “go/no-go gauge” to see if a part is either acceptable or unacceptable.
• Pinion. A round gear that is usually the smaller of two meshed gears. Its larger counterpart is called a bull gear. It can also be found in a rack and pinion system mated with a linear gear called a rack, or in a drivetrain.
• Pit Lathe. A pit lathe is a lathe built for short, large diameter work, intended to sit in a pit in a shop floor so that the toolrest will be waist high to the operator.
• Pitch. The term pitch in machining usually refers to spacing, either of cutting teeth or machined threads. In thread operations it is the distance from any point on a thread to the same point on an adjacent thread. In band saw blades, “tooth pitch” refers to the number of teeth per inch (abbreviated as TPI). In milling, pitch is the angular measure between teeth. Pitch can also refer to the number of inserts in a cutter (also called density).
• Pitch Diameter. The diameter of a thread at a point where both the width of the thread and the groove are the same.
• Plain Cutter. A type of milling cutter that only has cutting teeth on its outside edge.
• Plain Milling Machine. Another name for a horizontal mill.
• Planer Type Milling Machine. A large, heavy-duty mill that resembles a planer but has a milling spindle instead of a planing head. Planer-style mills are also called “plano millers.”
• Plug Gauge. A type of go/no-no gauge.
• Plunge Grinder. A type of outside diameter cylindrical grinder where the grinding wheel stays in contact with a single point on the workpiece, rather than traversing the length of it. 
• Plunge Milling. Also called Z-axis milling, it involves “plunging” the rotating cutting tool straight down into the workpiece to remove a large amount of material.
• Plunger Dial Gauge. Usually referred to as simply a “dial gauge,” it is a device that measures the amount its plunger or spindle is pushed up inside its casing.
• Pneumatic Press Brake. Sometimes called an air brake, a pneumatic press brake is a small machine that runs using shop air to move the ram for light gauge bending.
• Polishing. A finishing process that makes the surface of the part or material smooth and shiny through repeated rubbing or application of a chemical solution.
• Portable Drill. A portable drill is easily moveable around a worksite and is usually a handheld pistol-grip drill that is either plugged in or cordless with battery power.
• Portable Grinder. Another term for an angle grinder.
• Positive Rake Angle. A tool has a positive rake when the face of the cutting tool slopes away from the cutting edge at inner side. Tools with positive rake angles are usually sharper and more pointed than other styles, and they have lower power requirements. They can help avoid the formation of a built-up edge and as well as helping with the creation of continuous chips in ductile material. The strength of the tool may be compromised since the small angle of the tip makes it more susceptible to breakage.
• Power Screw. Another term for leadscrew.
• Precision Forging. A forging produced to closer tolerances than normally considered standard by the industry, eliminating most or all post-forging machining. Also known as close-tolerance forging.
• Profile. The side view of something is called its profile. In metalworking, it can refer to the shape of the end of a cutting tool or the shape of a long piece of metal when viewed from the end. An end mill with a “square profile” would have sharp cornered teeth at a 90° angle at the end, giving it a flattened appearance, while a cutter with a rounded end can be referred to as a “ball profile.” A piece of angle iron has a profile that looks like the letter “L,” while a pipe has a round profile. A profile roll, often called an angle roll, is a machine that can be adjusted to roll different profiles of long metal.
• Profile Gauge. Also called a contour gauge, a profile gauge uses a set of tightly grouped parallel pins that can independently move within a framework to make a cross-sectional impression of a surface when the pins are pushed up against it. The profile that has been captured in the arrangement of the pins can then be copied to another surface.
• Profile Projector. Another name for an optical comparator.
• Profile Roll. Commonly called an angle roll for its frequent use in bending angle iron, a profile roll is a machine used for bending different profiles of metal into curved shapes. The word profile can mean to look at something from the side, and the types of long metal pieces rolled by these machines have different shapes when seen end-on, such as angle iron with its L-shape. With the right tooling and high enough power, virtually any profile can be rolled, including C-section, flat bar, H-section, I-section, pipe, rectangular bar, round bar, round tube, square bar, square tube, and T-section.
• Profilometer. A type of surface roughness tester that can determine specifications such as curvature, flatness, and step by analyzing the topography of the part’s surface.
• Protractor. Protractors are tools for measuring angles. A simple protractor is a half-circle of transparent plastic or glass with marked angles that can be placed over a workpiece or layout. A bevel protractor is a metal tool with a straight-edge arm that can pivot away from the main arm or base and measure an angle between two sides of a workpiece.
• Punchout. The metal removed from a forging when a hole is punched in it.
• Push-cut Shaper. A shaper named after the direction of its cutting stroke.
• Pyramid 3-Roll Machine. The original type of sheet metal roll, a pyramid 3-roll has a symmetrical arrangement of one top roll centered over two bottom rolls. The other common type of 3-roll sheet metal roll is an initial pinch roll, which is an asymmetrical roll with two pinch rolls on one side and an adjustable roll on the other.
• Pyrometer. A device used in a heat-treating furnace to measure high temperatures.