NCCER Millwright key terms

A safety procedure in which energy-isolating devices are locked and tagged so equipment cannot be started or energized while workers service it. Only the person who applied the lock removes it.

Specialized clothing and gear such as hard hats, safety glasses, gloves, and hearing protection worn to reduce exposure to workplace hazards. Employers select PPE based on the hazards identified for each task.

A step-by-step review of a task that identifies hazards in each step and lists controls to reduce risk before work begins. It is also called a job safety analysis.

An enclosed area with limited entry and exit that is not designed for continuous occupancy, such as a tank or pit. Entry may require testing, ventilation, an attendant, and a permit.

A hand tool that applies a measured twisting force to a fastener and signals when the preset value is reached. It is used where fasteners must be tightened to a specified torque.

A lifting device with a chain and hook that uses hand or power to raise and lower loads. A ratchet or friction brake holds the load when the operator releases the pull chain.

A lifting tool that uses pressurized fluid in a cylinder to raise heavy loads with little effort. It must sit on a firm, level surface and be rated above the load being lifted.

A drawing method that shows an object from multiple views, usually front, top, and side, arranged on one sheet. Each view shows true shape and size for the dimensions it faces.

A three-dimensional style of drawing in which the three axes are drawn 120 degrees apart. It shows length, width, and height in one view and is common for piping layouts.

A schematic that shows process piping, equipment, valves, and instruments using standard symbols and tag numbers. It is the main reference for tracing and troubleshooting a process system.

A list, usually on the drawing or attached to it, that identifies each part, its quantity, and often its material or part number. It is used to order and verify components.

A precision measuring instrument with a calibrated screw that measures outside or inside dimensions to thousandths of an inch or hundredths of a millimeter. The spindle closes on the part and the thimble is read.

A measuring instrument with a spring-loaded plunger and a graduated dial that shows small movements or variations. It is used for checking runout, flatness, and alignment.

A measuring tool with a fixed and sliding jaw and a vernier scale that reads outside, inside, and depth dimensions. It is versatile but generally less precise than a micrometer.

The total amount a dimension is allowed to vary from its stated value, expressed as a plus and minus range or as limits. Parts must fall within tolerance to fit and function correctly.

A reference point, line, or surface from which measurements and dimensions are taken. Datums establish a common starting point so drawings, layouts, and parts agree with one another.

The point at which the weight of an object is considered to act as if concentrated. The hoist hook must be directly above it for a level, stable lift.

The angle between a sling leg and the horizontal. As the angle gets smaller, the tension in the sling increases, so the rated capacity of the sling is reduced.

A U-shaped rigging fitting with a pin or bolt that connects slings to loads or lifting points. It must be rated for the load and pulled only along its intended axis.

A manufacturer's table or graph listing the maximum load a crane or hoist can lift at a given radius, boom length, and configuration. It must be consulted before every lift.

A rope attached to a load so a worker can control its rotation and swing from a safe distance. It keeps hands off the load while guiding it into place.

A condition in which one foot of a machine does not sit flat on its base, causing the frame to distort when the bolt is tightened. It must be corrected before alignment begins.

A cementitious or epoxy material poured under a baseplate to fill gaps, spread load, and damp vibration. It is placed after the machine is leveled and before final alignment.

A bolt embedded in concrete or masonry that holds a baseplate or machine to its foundation. It is fitted with a nut and washer and tightened after the machine is aligned.

A shaft alignment method using dial indicators to measure runout on the coupling rim and face. Readings show parallel and angular misalignment, which are corrected by shimming and moving the machine.

A shaft alignment technique in which two dial indicators are mounted on opposite shafts and rotated together. The readings, combined with measured dimensions, give the shim and move corrections.

A method using laser transmitters and receivers mounted on the two shafts to measure offset and angularity electronically. It calculates the corrections needed and is fast and accurate.

A condition in which the centerlines of two shafts meet at an angle rather than running parallel. It shows up as a coupling gap that changes across the face.

A condition in which two shaft centerlines are parallel but offset from each other, so the coupling rims do not line up. It is corrected by moving or shimming the machine.

A bearing that uses rolling elements such as balls or rollers between inner and outer rings to carry load with low friction. It requires proper lubrication and correct fitting.

A plain bearing in which a shaft rotates on a film of oil inside a sleeve or split housing. It carries heavy loads and requires a continuous supply of lubricant.

A flexible sealing ring with a lip that presses against a rotating shaft to keep lubricant in and dirt out. It is also called a radial shaft seal.

A sealing assembly with two flat, lapped faces, one rotating with the shaft and one stationary, held together by spring pressure. It prevents leakage where a pump shaft passes through the casing.

A measure of a fluid's resistance to flow, which changes with temperature. Selecting the correct viscosity ensures the lubricant forms a film that protects the bearing surfaces.

A valve that opens automatically to release fluid when pressure exceeds a set value, protecting the system from damage. It is a safety device and is not used to control flow.

A pressure vessel that stores hydraulic fluid under gas pressure and releases it to absorb shock or supply extra flow. It must be discharged before any maintenance is done.

A combination of filter, regulator, and lubricator used in a compressed-air line to clean the air, set the pressure, and add oil mist. It is installed ahead of pneumatic components.

A predictive maintenance technique that measures machine vibration to detect imbalance, misalignment, and bearing wear before failure. Trends and frequency patterns point to the specific fault.

A predictive maintenance method that uses an infrared camera to find abnormal temperature patterns in equipment. Hot spots can indicate loose connections, excess friction, or failing bearings.

A predictive maintenance practice in which lubricant samples are tested for wear particles, contamination, and additive depletion. Results guide oil changes and warn of internal wear.