Free NCCER Millwright Exam Flashcards

A micrometer measures an absolute dimension (a part's actual size in thousandths of an inch). A dial indicator measures relative displacement — how far a surface moves or wobbles compared to a zero reference — which is why it's used for runout and alignment, not for reading a part's true dimension.

The ratchet stop slips at a fixed, repeatable measuring force once the anvils contact the part, so every technician gets the same reading regardless of hand strength. Cranking the thimble directly risks over-tightening, which springs the frame and gives a false, too-small reading.

The barrel and thimble alone read to 0.001 in. The vernier scale on the sleeve adds a third set of graduations that lets you interpolate one more digit, resolving measurements down to 0.0001 in for tighter tolerance work.

Feeler gauges (stacked thin steel leaves) check a physical gap you can slide a blade into, such as soft-foot clearance, valve lash, or coupling gaps. A dial indicator instead tracks movement or runout over a rotation, not a static gap.

It measures internal bore diameters, such as bearing housings or cylinder bores, from the inside out. An outside micrometer only spans external dimensions like shaft diameters, so the two tools aren't interchangeable.

An optical level with a target rod establishes a true horizontal plane across a room, used to compare elevations of multiple baseplates or foundations. A laser alignment system instead measures the offset and angle between two coupled shafts — it does not establish a room-wide reference plane.

Flatness of a baseplate, soleplate, or machined mounting surface, usually checked with a feeler gauge slid underneath. A warped or non-flat mounting surface causes soft foot and defeats alignment no matter how carefully the shafts are indicated afterward.

Bolting down a machine with soft foot twists the frame the moment the bolts are torqued, which shifts the shaft centerline and undoes the alignment just dialed in. Soft foot must be shimmed out before final alignment, not after.

A star pattern applies clamping force evenly across the base in progressive passes, letting the machine settle uniformly onto the foundation. Tightening bolts sequentially from one end can rock or warp the base before the far bolts are even snug.

They provide fine, controlled vertical or horizontal adjustment of a machine's position before final bolt-down, moving the frame a few thousandths at a time so the millwright isn't prying on the casing with a bar to nudge it into rough position.

Dowel pins lock a machine's exact aligned position so it can be removed for maintenance and reinstalled in the identical spot without re-aligning from scratch. Installing them earlier would just fix a wrong position permanently in place.

A Woodruff key is a semicircular key that seats in a curved keyseat, self-aligning on tapered or smaller-diameter shafts in light-to-moderate torque applications. A straight rectangular key is used on larger, higher-torque shaft sections and doesn't accommodate shaft taper the way a Woodruff key does.

A gib-head key has an angled, protruding head so it can be driven out with a hammer and drift from the accessible side, useful where the far end of the keyway is blocked by a hub or housing and can't be pushed through.

Offset misalignment means the two shaft centerlines stay parallel but are displaced side to side. Angular misalignment means the centerlines intersect at an angle instead of running parallel. Most real-world misalignment is a combination of both, which is why alignment methods solve for each independently.

Misalignment forces the coupling and bearings to absorb cyclic bending loads on every rotation instead of just transmitting torque. That constant flexing shows up as vibration, accelerated bearing wear, coupling failure, seal leakage, and higher energy draw long before it's visible without instruments.

Machine casings and shafts grow as they heat up in operation. The millwright calculates expected thermal growth and sets the cold, shutdown alignment numbers off-center by that amount, so once the machine reaches operating temperature the shafts settle into true alignment.

Reverse-indicator mounts one indicator on each shaft, each reading the other shaft's OD at two axial points, so no face (thrust-surface) reading is needed. Rim-and-face instead reads one shaft's rim and its own coupling face, which can introduce error if that shaft has axial float — reverse-indicator avoids that error source.

The bracket bridging across the coupling to hold the indicators deflects slightly under its own weight, adding a small constant error to every reading. Millwrights measure this sag on a test stand beforehand and subtract it from field readings so it isn't mistaken for real misalignment.

Rotating both shafts together and capturing readings at four points around the coupling separates vertical misalignment (top vs. bottom readings) from horizontal misalignment (side vs. side readings), giving the two correction values needed to shim and move the machine.

Precut thin metal shims are added under, or removed from, a machine's feet to make vertical corrections only. Horizontal correction is made by moving the machine sideways on the baseplate — shims can't fix a side-to-side offset, only up-and-down position.

A dominant vibration peak at 1X running speed typically points to rotor unbalance. A strong peak at 2X running speed is the classic signature of shaft misalignment. Reading which frequency dominates lets a millwright narrow down the likely cause before opening up the machine.

An anti-friction bearing uses rolling elements, balls or rollers, between the races so contact is rolling, not sliding. A plain/sleeve bearing instead relies on a thin hydrodynamic film of oil between the shaft and a smooth sleeve — no rolling element at all, just a fluid wedge carrying the load.

Controlled heating with an induction heater or oil bath expands the bearing bore just enough to slide it onto the shaft with no impact force, avoiding brinelling of the races. Heating is kept below roughly 250°F, since higher temperatures can alter the bearing steel's hardness and shorten its life.

L10 is the statistical revolution or hour count at which 90% of a group of identical bearings, run under the same load and speed, are still surviving — meaning up to 10% could fail before reaching that point. It's a probability rating, not a guaranteed lifespan for any single bearing.

True brinelling is permanent race indentation from a static overload or impact. False brinelling looks similar but comes from fretting: small vibratory movement while the bearing sits stationary, such as during shipping, which wears a pattern into the race without any single overload event.

Grease stays in place with minimal sealing and needs less maintenance, making it the default for moderate speeds and hard-to-seal locations. Oil dissipates heat better and can be circulated, filtered, and cooled, so it's favored for high-speed or high-temperature applications where grease would break down.

Packing a bearing housing completely full leaves no room for the grease to churn and circulate, so it overheats and can push past seals under pressure. The correct fill is typically only about one-third to one-half of the housing's free space, not 100%.

Spalling, flaking or pitting of the race surface, indicates subsurface metal fatigue from repeated cyclic loading over time, not a single contamination event. It points toward normal fatigue life being reached or overload, distinct from the scoring or discoloration you'd see from contamination or lubrication failure.

A centrifugal pump's flow rate varies with discharge pressure — throttling a valve changes how much it delivers. A positive-displacement pump moves a fixed volume per revolution regardless of pressure, which is why it needs a relief valve: a blocked discharge builds pressure rather than just reducing flow.

NPSH required (NPSHr) comes from the pump manufacturer's curve: the minimum suction-side pressure margin that specific pump needs to avoid cavitation. NPSH available (NPSHa) is calculated from the actual system layout. You must keep NPSHa above NPSHr, not the other way around.

Cavitation happens when local pressure at the impeller drops below the fluid's vapor pressure, forming vapor bubbles that collapse violently and pit the impeller. Gas binding happens when entrained air or gas physically displaces liquid at the impeller eye, causing the pump to lose prime, with no vapor-bubble collapse or pitting involved.

A mechanical seal uses two flat, lapped faces, one rotating and one stationary, pressed together to create a near-zero-leakage barrier. A packing gland instead compresses rings of packing material around the shaft and is designed to allow a small, controlled drip — that leakage is what lubricates and cools the packing.

It circulates clean, compatible fluid across the seal faces to cool them, lubricate them, and flush away abrasive particles from the process fluid. Without a flush plan, dirty or hot process fluid reaching the seal faces directly can score them and cause early seal failure.

With no flow moving through the casing, the trapped fluid keeps recirculating past the impeller and heats up rapidly. That heat can flash the fluid to vapor, damaging the mechanical seal and bearings and causing severe vibration, even though the pump isn't visibly doing anything from outside.

It sets how much high-pressure fluid can recirculate internally from the pump's discharge side back to the low-pressure suction side. As wear rings wear and the clearance opens up, more fluid recirculates internally and the pump loses head and efficiency even though nothing else about it has changed.

A V-belt wedges into a grooved pulley, using that wedging action to boost friction and torque capacity. A flat belt relies on plain surface friction with lower torque capacity. A timing belt has teeth that engage a toothed sprocket, giving a positive, slip-free drive that keeps exact rotational synchronization.

An over-tensioned belt overloads the bearings and shafts, showing up as premature bearing failure even though the belt itself may look fine. An under-tensioned belt instead slips, glazes, overheats, and can whip — power loss and belt wear are the tell, not bearing wear.

The chain doesn't literally stretch — wear at the pin-and-bushing joints lets each link grow slightly longer, and that adds up across the chain's full length. Beyond a manufacturer's elongation limit, the chain no longer meshes correctly with the sprocket teeth and can jump or skip.

It reduces rotational speed in the same proportion that it increases torque, so the motor can run at its efficient rated speed while the driven equipment gets the lower speed and higher torque it actually needs.

Belt tracking problems usually trace to uneven tension side-to-side, pulleys that aren't crowned or aligned correctly, or material buildup on a pulley face that's effectively changing its diameter on one side. It's rarely the belt itself that's at fault.

It allows the conveyor to run forward normally but mechanically prevents it from reversing if drive power is lost. On an incline, a loaded belt without a backstop would run backward under gravity, which can damage equipment and endanger anyone near the discharge end.

A reciprocating compressor uses a piston moving in a cylinder to compress gas in discrete pulses per stroke. A rotary screw compressor uses two meshing helical rotors to compress gas continuously, giving smoother, less pulsating discharge flow.

Compression heats the gas and increases its volume; removing that heat between stages shrinks the gas back down before the next stage compresses it further. This improves overall efficiency and protects downstream seals and lubricants from excess heat buildup.

It senses the turbine's shaft speed and automatically adjusts the steam admission valve to hold the desired speed as load changes, preventing the turbine from overspeeding if load drops suddenly.

Tighter clearances between blades and the casing reduce gas or steam bypass, directly improving efficiency. But that same tightness means even a small misalignment or imbalance can cause a rub at high rotational speed, with far more severe consequences than on lower-speed equipment.

Pressure differences across the rotating stages push the rotor along its axis (axial thrust). A thrust bearing absorbs that force, holding the rotor in its correct axial position so rotating and stationary parts don't come into contact.

The sling or rope used must have a rated breaking strength at least 6 times the maximum load it will actually lift. That margin covers wear, minor shock loading during the lift, and the gap between periodic inspections; it isn't extra capacity for lifting heavier loads.

As the angle between a sling leg and the horizontal gets shallower (legs spread wider), the tension carried by each leg increases sharply, well beyond the load's actual weight. Rigging capacity charts specify a given angle because the same sling has much less capacity spread at a shallow angle than rigged near-vertical.

Lift points have to be positioned so the load's center of gravity hangs directly under the hook, keeping it level and stable in the air. Misjudging center of gravity on an odd-shaped load risks it tipping or sliding during the lift, not just hanging crooked.

Switching off a control doesn't stop someone else from switching it back on. LOTO physically locks each energy source, electrical, hydraulic, pneumatic, or mechanical, in the isolated position and tags it, so the machine can't be re-energized while a millwright is inside or working on it.