MMAW NC II cheat sheet

PPE hierarchy for mechatronics work: safety glasses under a face shield when grinding; insulated gloves rated to the measured voltage for live testing; safety shoes with toe caps in assembly areas; hearing protection above 85 dBA TWA.

Lockout/tagout sequence: notify, shut down, isolate all energy sources (electrical, pneumatic, hydraulic, gravity, stored spring), dissipate residual energy, verify zero energy, apply personal lock and tag; only the person who applied a lock removes it.

Five steps of 5S: Seiri (sort), Seiton (set in order), Seiso (shine), Seiketsu (standardize), Shitsuke (sustain); audit scores below target trigger corrective action, not blame.

Color tags in 5S sorting: red tag = remove/redesignate item; yellow tag = relocate or reassign; the red-tag holding area has a defined review date.

Electrical safe work: treat circuits as energized until tested with a proven meter; test the meter on a known live source before and after the zero-energy check.

Arc flash boundary and approach boundaries are set from the incident energy label; unqualified persons stay outside the arc flash boundary, qualified persons use rated PPE inside.

Environmental rules: spent solvents, oily rags, and used filters are hazardous waste, never general trash; waste containers stay closed and labeled with contents and date.

Emergency response order: raise alarm, de-energize if safe, evacuate or isolate, then report; an incident report is filed even for a near miss.

Confined space and hot work require a permit; a fire watch stays in place at least 30 minutes after hot work ends unless site rules state longer.

First-angle projection: the view placed below the front view is the top view; third-angle: the view below the front view is the bottom view. Check the projection symbol (truncated cone) on the drawing.

Line conventions: visible outline = continuous thick; hidden feature = dashed; center line = long-short chain; cutting plane = thick chain with arrows showing view direction.

Scale notation 1:2 means drawing is half size; a dimension printed on the drawing always overrides a scaled measurement taken from the paper.

Tolerance stack: limit dimensions give the max and min directly; bilateral tolerance ±x gives a total zone of 2x; fit designation H7/g6 is a clearance fit (hole letter uppercase, shaft lowercase).

GD&T symbols: flatness, straightness, circularity, cylindricity are form (no datum); perpendicularity, parallelism, angularity are orientation (datum required); position, concentricity, symmetry are location.

Pneumatic symbol reading: box = directional valve, number of boxes = positions, number of ports per box = ways; external pilot lines are dashed, working lines solid.

Electrical schematic: normally open contacts drawn in de-energized state; a component's reference designator (K1, Q1, M1) links the coil to its contacts across sheets.

Work instruction structure: sequence of steps, tools and torque values, quality checkpoints, and safety notes; a revision block change must be verified before starting the job.

Vernier caliper resolution: main scale division / number of vernier divisions; a 0.02 mm caliper has 50 vernier divisions over 49 mm. Read main scale at the vernier zero, then add the coinciding vernier line × 0.02 mm.

Micrometer reading: barrel scale in 0.5 mm increments plus thimble reading × 0.01 mm; a 0-25 mm micrometer has one full thimble turn = 0.5 mm.

Zero error check: close the jaws/faces on a clean gauge; a caliper that reads other than 0.00 has zero error to be added or subtracted from every reading.

Torque wrench: applied torque = set torque; never use a torque wrench as a breaker bar; recalibrate after drops or per interval, and store at the lowest scale setting.

Hacksaw and file: cut on the forward stroke, keep the blade tensioned, use a file card to clean the file; never use a file without a handle.

Measurement accuracy rules: choose an instrument with resolution about 1/10 of the tolerance; measure at 20 °C reference temperature; avoid parallax by reading scales straight on.

Dial indicator: one revolution of the pointer equals the spindle travel of the chosen tip; use for runout, concentricity, and shaft alignment (rim and face readings).

Feeler gauge and straightedge check flatness and clearance; a feeler gauge must drag slightly, not pass freely, to indicate the correct clearance.

Ohm's law: V = I × R; power P = V × I = I²R = V²/R.

Series circuit: R_total = R1 + R2 + …; current is common; voltage divides in proportion to resistance.

Parallel circuit: 1/R_total = 1/R1 + 1/R2 + …; voltage is common; current divides inversely with resistance.

Kirchhoff's laws: sum of currents at a node = 0; sum of voltages around a closed loop = 0.

Three-phase: line voltage = √3 × phase voltage in star (wye); line current = √3 × phase current in delta; power = √3 × V_line × I_line × power factor.

Diode: forward drop about 0.7 V (silicon) or 0.3 V (germanium); a rectifier bridge converts AC to pulsating DC; a Zener regulates in reverse breakdown.

Transistor as switch: base-emitter about 0.7 V to conduct; NPN conducts when base is positive relative to emitter; PNP when base is negative.

Capacitor and inductor behavior: capacitor opposes voltage change (open at DC steady state); inductor opposes current change (short at DC steady state); time constant τ = RC or L/R.

Continuity and insulation testing: a good conductor reads near 0 Ω; insulation resistance is measured with a megohmmeter at the rated test voltage, never on an energized circuit.

Boyle's law for pneumatics at constant temperature: P1V1 = P2V2; free air consumption = cylinder volume × (working pressure + 1) / atmospheric pressure, in bar absolute.

Cylinder force: F = P × A; retract force uses the annulus area A = π(D² − d²)/4, extend force uses the bore area πD²/4.

Speed control: meter-out (exhaust throttling) gives stable control of a running-away load; meter-in suits loads that resist motion; both use a flow control valve with check.

5/2 double-solenoid valve has memory (stays in last position on power loss); 5/2 single-solenoid with spring return goes to the home position when de-energized.

Hydraulic pressure is set by the relief valve, not the pump displacement; the pump delivers flow, the load creates pressure.

Accumulators store energy and must be pre-charged and depressurized before maintenance; hydraulic fluid is incompressible so pressure builds almost instantly.

Air preparation unit order (FRL): filter, regulator, lubricator; the regulator sets downstream pressure and needs a relief path to reduce setting.

Symbol rules: dashed line = pilot/leakage, solid = main flow; a triangle with a point shows flow direction; a spring on the valve end indicates default position.

Actuator sizing check: rod buckling, cushioning at end of stroke, and air consumption per cycle are verified against the duty cycle, not just force.

Sensor output types: PNP (sourcing) switches the positive supply to the load; NPN (sinking) switches the load to 0 V; PLC input common must match the sensor type.

Inductive sensors detect metal only, short range, no moving parts; capacitive sensors detect most materials including liquids; photoelectric types are through-beam, retro-reflective, and diffuse.

NPN/PNP naming refers to the transistor inside the sensor, not to the load; a 3-wire sensor has supply +, supply −, and output.

Encoder: incremental gives pulses per revolution and needs a home reference; absolute gives position directly after power-up; quadrature A/B channels give direction and ×4 resolution.

Relay and contactor: coil voltage separate from contact rating; contactor for motor loads with overload relay; interlock so forward and reverse coils cannot energize together.

Proximity sensor mounting: respect the correction factor for non-ferrous targets (about 0.7 for brass/aluminum) and keep a safety distance from the sensing face.

Actuator types: solenoid, motor, and pneumatic cylinder; a stepper motor position is set by pulse count, a servo by closed-loop feedback.

Analog signal standards: 4-20 mA (live zero detects broken wire), 0-10 V, and RTD/thermocouple for temperature; 4 mA = 0 % and 20 mA = 100 % of span.

PLC scan cycle: read inputs, execute program, update outputs, housekeeping; scan time affects response to fast pulses, so use interrupt or high-speed counter inputs.

Ladder logic: XIC = examine if closed (normally open), XIO = examine if open (normally closed), OTE = output energize, OTL/OTU = latch/unlatch, TON/TOF/RTO timers, CTU/CTD counters.

Sinking input module expects the field device to supply +V (PNP sensor); sourcing input module expects the device to pull to 0 V (NPN sensor).

Digital output types: relay (AC/DC, slow), transistor (DC, fast, no inrush tolerance), triac (AC only); never connect a triac output to a DC load.

Troubleshooting order: check power and module indicators, then input LEDs with a forced test, then the program rung state, then output device and wiring.

A forced output stays forced through run mode and is dangerous; forces must be removed and recorded before handover.

Analog scaling: engineering value = ((raw − raw_min)/(raw_max − raw_min)) × (eng_max − eng_min) + eng_min.

Communication: RS-485/Modbus and Ethernet/IP are common; verify baud rate, node address, and termination resistor before blaming the program.

Bolt preload: torque is a proxy for preload; about 90 % of applied torque goes to friction; use the specified lubricant because it changes the torque-preload relationship.

Thread and fastener rules: right-hand thread tightens clockwise; grade marking (e.g., 8.8) gives tensile strength; use the correct thread pitch gauge before chasing a damaged thread.

Bearing installation: press on the race that carries the interference fit (inner race on a shaft); never transmit mounting force through the rolling elements.

Shaft alignment: rim and face or reverse dial indicator method; acceptable misalignment is typically under 0.05 mm; check soft foot before alignment.

Belt tension: measure deflection at the mid-span with a specified force; too tight damages bearings, too loose causes slip and heat.

Gear and coupling checks: backlash, tooth contact pattern, and coupling gap are recorded; a worn coupling causes vibration at 2× running speed.

Preventive maintenance schedule: lubrication interval, filter change, vibration trend, thermography, and torque re-check; condition-based tasks trigger on trend limits, not calendar alone.

Vibration analysis: unbalance shows 1× running speed, misalignment 2×, looseness harmonics, bearing defect at high-frequency multiples.

Fault-finding sequence: observe the symptom, gather history, form a hypothesis, test by half-split, confirm the root cause, repair, then verify the whole system.

Half-split method reduces the search: test at the mid-point of the signal chain, then work toward the faulty half; each test must be able to confirm or eliminate.

Commissioning order: mechanical check, electrical insulation and continuity, power-up without load, I/O check, manual jog, then automatic cycle and safety function test.

Safety function verification: test the emergency stop, guard interlock, and light curtain by actually tripping them and confirming the hazardous motion stops.

Intermittent faults: check connectors, cable routing near drives, grounding, and thermal effects; log time-stamped events to correlate with machine state.

Signal tracing: verify supply at the source, then at each terminal; a voltage present at the load with no current flow indicates an open return path.

Test record content: instrument used and calibration date, measured value versus specification, ambient condition, and pass/fail with signature.

After repair, re-run the full cycle and update the drawing and maintenance record; an undocumented change becomes the next fault.