NCCER Millwright flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Zero Energy Verification

After isolating and locking out all energy sources, attempt a normal start and test for residual voltage or pressure; the machine must not move or energize.

Permit Space Oxygen Limits

A permit-required confined space may be entered only when oxygen is between 19.5 and 23.5 percent by volume and other atmospheric hazards are within accepted limits.

Fall Protection Heights

OSHA requires fall protection at 4 feet in general industry workplaces and at 6 feet in construction, using guardrails, nets, or personal fall arrest systems.

Torque Formula

Torque equals force multiplied by lever arm length; 100 pounds applied two feet from a fastener develops 200 foot-pounds of torque.

Micrometer Least Count

A standard inch micrometer reads to 0.001 inch because the thimble has 25 divisions spanning a 0.025 inch barrel graduation; metric micrometers typically read 0.01 millimeter.

Crowfoot Extension Correction

An adapter at 90 degrees to the wrench handle requires no setting change, but an in-line extension increases effective length and requires a lower wrench setting.

Third-Angle Projection Layout

In third-angle projection the top view is drawn above the front view and the right side view is drawn to the right, the standard convention in North American drawings.

Drawing Scale Ratio

A scale of one-quarter inch equals one foot means one quarter inch on paper represents twelve inches of the part, a ratio of 1:48.

Hidden Line Convention

Hidden edges are drawn as medium-weight dashed lines; centerlines use a long-short-long pattern to mark axes, bolt circles, and symmetry.

Sine Bar Formula

The sine of the set angle equals the gage block stack height divided by the center distance between the bar's rolls, commonly 5 or 10 inches.

Total Indicated Runout Defined

TIR is the total spread between the highest and lowest dial indicator readings in one revolution, used to judge shaft straightness, hub eccentricity, and journal condition.

Standard Measurement Temperature

Precision dimensional measurements are referenced to 68 degrees Fahrenheit (20 degrees Celsius) because steel expands about 6.5 micro-inches per inch for each Fahrenheit degree.

Two-Leg Sling Tension

For a symmetric two-leg lift, tension per leg equals load divided by twice the cosine of the angle from vertical; at 60 degrees from horizontal each leg carries 0.577 times the load.

Sling Load Angle Factor

The multiplier found by dividing sling length by vertical lift height; a factor of 1.155 means each leg carries 1.155 times its share of the load.

Chain Sling Removal Criteria

Remove a chain sling from service when link diameter wears more than 10 percent, when the chain is stretched, or when cracks, nicks, or bent links are found.

Soft Foot Limit

A machine foot that does not sit flat distorts the frame when its bolt is tightened; the measured gap should not exceed 0.002 inch.

Pipe Strain Test

Mount a dial indicator on the shaft or coupling, loosen the pipe flange bolts, and check for movement; more than 0.002 inch indicates strain that must be corrected.

Shim Stack Rules

Place shims directly beneath the foot, use pre-cut stainless steel, and limit the stack to about four shims so the pack does not compress and lose bolt preload.

Angular Misalignment Definition

A condition where the gap between coupling faces changes across the diameter, expressed as a slope in thousandths of an inch per inch of coupling diameter.

Rim and Face Correction

Required shim change equals the face reading divided by coupling diameter, multiplied by the distance from the coupling to the foot being corrected.

Rotation During Alignment

Turn both shafts together while taking readings so that runout of the coupling hubs and shafts cancels out and does not appear as misalignment.

Bearing Bore Code

In a designation such as 6205, the last two digits multiplied by five give the bore in millimeters, so 05 means a 25 millimeter bore.

Grease Fill Percentage

Bearings and housings are typically filled to 30 to 50 percent of free space; overfilling causes churning, heat, and premature grease breakdown at high speed.

Lip Seal Orientation

The spring-loaded sealing lip faces the lubricant it retains and the spring side faces the medium; a second lip is added to exclude external contamination.

Bearing Heating Limit

Sealed or pre-greased bearings should not be heated above about 250 degrees Fahrenheit (120 degrees Celsius) because higher temperatures damage the lubricant and elastomer seals.

Cylinder Force Equation

Force equals hydraulic pressure multiplied by effective piston area; on the rod side, subtract the rod cross-sectional area from the piston area before multiplying.

Accumulator Precharge Gas

Bladder and piston accumulators are charged with dry nitrogen only, because oxygen or air mixed with hydraulic oil under pressure can ignite or explode.

Filter Regulator Lubricator Function

An FRL unit removes water and dirt from compressed air, regulates downstream pressure, and adds a controlled oil mist for pneumatic tools and valves.

One Times RPM Peak

A dominant vibration peak at shaft rotational frequency with few harmonics indicates unbalance; a strong two-times peak instead points to misalignment or a bent shaft.

Thermography Loose Connections

Infrared scanning performed under normal load reveals high-resistance electrical joints and overloaded circuits as hot spots before they fail or cause a fire.

Bathtub Curve Phases

Failure rate follows three phases: infant mortality from defects, a random constant-rate period, and a rising wear-out period that scheduled replacement targets.

Oil Analysis Wear Metals

Laboratory reports flag iron, copper, chromium, and lead along with viscosity, water content, and particle counts to reveal wear, contamination, and lubricant breakdown.