Mechanical Engineering Vocabulary: 100 Key English Terms
Mechanical engineers read English every day: drawings, datasheets, standards, supplier catalogs, test reports and maintenance manuals are very often written in it. Knowing the core vocabulary of mechanics, machine elements, manufacturing, thermodynamics and maintenance helps you talk to suppliers and customers, follow international projects and explain a design or a failure clearly.
100 terms
10 topics
47 core terms
204 example sentences
Read, understand, keep going
No account needed. Read the meaning, see where the term is used, then study the examples. Click any word in the lesson for help. You can also select a word and press Alt + Enter.
Mechanics and Materials
stress
noun
Meaning
The internal force inside a material divided by the area it acts on. It shows how hard a part is being pulled, pushed, bent or twisted and is measured in MPa or psi.
Where you use it
Used constantly in design reviews and calculations. Engineers calculate, check and reduce stress, and talk about tensile, compressive, shear and bending stress. A stress concentration is a local peak, for example at a sharp corner or a hole.
Examples
The maximum stress in the bracket is 180 MPa, well below the yield strength of the steel.
Add a fillet here to reduce the stress concentration at the corner.
Usage note
In mechanical engineering stress means gerilme, not psychological 'stres'. Turkish speakers also mix it up with 'gerilim', which in engineering Turkish usually means electrical voltage.
How much a material stretches or shortens compared with its original length. It is a ratio with no unit and is often given in percent or in microstrain.
Where you use it
Used in materials testing, stress analysis and measurements. Strain is measured with strain gauges glued to the part, and engineers talk about elastic strain, plastic strain and the stress-strain curve.
Examples
We bonded two strain gauges to the beam to measure the strain under load.
At this point the strain is no longer elastic, so the part will not return to its original shape.
Usage note
Stress is the cause (force per area) and strain is the result (change in length). Mixing the two up is a common mistake in reports.
A force, weight or pressure that acts on a part or structure. Loads can be steady or changing and are the starting point of most strength calculations.
Where you use it
One of the most common words in design and testing. Engineers apply, carry and withstand loads, and distinguish static, dynamic, axial, radial and cyclic loads. It is also used for motors and machines: full load, part load, no load.
Examples
The bearing has to carry a radial load of 12 kN.
The frame failed under cyclic load after about 200,000 cycles.
Run the pump at full load for two hours and record the temperatures.
Common phrases
apply a load · axial load · radial load · load capacity · under load
A turning force that makes something rotate around an axis, such as a shaft or a bolt. It equals force times distance and is measured in newton meters (N·m).
Where you use it
Used for motors, gearboxes, shafts and fasteners. A motor produces torque, a gearbox increases it, and bolts are tightened to a specified torque with a torque wrench. In the US it is often given in pound-feet (lb-ft).
Examples
Tighten the flange bolts to a torque of 45 N·m in a cross pattern.
The motor produces its maximum torque at low speed.
Usage note
Many Turkish texts translate both torque and moment as 'moment'. In English, torque usually describes twisting (a shaft, a bolt), while bending moment is used for beams.
The stress at which a material stops behaving elastically and starts to deform permanently. Designers usually keep working stresses well below this value.
Where you use it
Appears on every material datasheet and in strength calculations, usually next to tensile strength. For metals without a clear yield point, the 0.2% offset value is used. Engineers say a part 'yielded' when it bent permanently.
Examples
S355 steel has a minimum yield strength of 355 MPa for thin sections.
The calculated stress is close to the yield strength, so we need a thicker section.
Common phrases
minimum yield strength · exceed the yield strength · yield point · 0.2% offset · yield and tensile strength
Gradual damage and cracking of a material caused by loads that are applied and removed many times, even when each load is below the material's static strength.
Where you use it
A key term in machine design, especially for shafts, springs, welds and rotating parts. Engineers talk about fatigue life, fatigue strength, fatigue cracks and the S-N curve. A part 'fails in fatigue' and often shows typical beach marks on the fracture surface.
Examples
The shaft broke due to fatigue, not overload; you can see the beach marks on the fracture surface.
We need to check the fatigue life of the welds for ten million cycles.
Usage note
Pronounced 'fuh-TEEG', with the stress on the second syllable. In everyday English the same word means tiredness.
Common phrases
fatigue life · fatigue strength · fatigue crack · fatigue failure · metal fatigue
How far a beam, shaft or other part bends or moves away from its original position when a load is applied, usually measured in millimeters.
Where you use it
Used in structural and machine design. Engineers calculate, limit and measure deflection; a design may be strong enough but still unusable because it deflects too much. Limits are often written as a fraction of the span, such as L/500.
Examples
The maximum deflection of the beam under full load is 1.8 mm.
The shaft deflection is too high, and it is affecting the gear mesh.
The turning effect of the loads that makes a beam or shaft bend at a certain point. It equals force times distance and is given in N·m or kN·m.
Where you use it
Used in strength of materials, structural design and shaft calculations. Engineers draw a bending moment diagram, find the maximum bending moment and use it to calculate bending stress. For a simply supported beam with a central load P and span L, the maximum is PL/4.
Examples
The maximum bending moment occurs at the middle of the span.
Draw the shear force and bending moment diagrams before you size the beam.
Common phrases
bending moment diagram · maximum bending moment · shear force · bending stress
A material property that shows how stiff a material is: the ratio of stress to strain in the elastic range. It is about 200 GPa for steel and 70 GPa for aluminum.
Where you use it
Used in material selection, deflection calculations and FEA. Often called Young's modulus and written E. A higher modulus means less deflection under the same load, but it does not mean higher strength.
Examples
Aluminum's modulus of elasticity is about one third of steel's, so the same bracket in aluminum will deflect about three times as much.
Enter the modulus of elasticity and Poisson's ratio of the material before you run the simulation.
Common phrases
Young's modulus · elastic modulus · modulus of elasticity of steel · Poisson's ratio
The ratio between the load or stress a part can withstand and the load or stress it actually carries in use. A value of 2 means the part is twice as strong as needed.
Where you use it
Used in every strength calculation and design review. Also called safety factor and written FoS or SF. The value chosen depends on how well the loads and materials are known and on how serious a failure would be.
Examples
With a yield strength of 355 MPa and a maximum stress of 142 MPa, the factor of safety is 2.5.
Lifting equipment needs a higher factor of safety than a simple machine cover.
Common phrases
safety factor · minimum factor of safety · apply a factor of safety · design factor
How well a material resists being scratched, dented or worn at its surface. It is measured with tests such as Rockwell (HRC), Brinell (HB) or Vickers (HV).
Where you use it
Used on drawings, heat treatment specifications and inspection reports. Engineers specify, measure and check hardness, and parts are hardened to increase it. It is written with its scale, for example 58–62 HRC, and is closely linked to wear resistance.
Examples
The drawing calls for a surface hardness of 58–62 HRC after heat treatment.
We measured the hardness at five points and all values were within the range.
Usage note
Do not confuse hardness (resistance to surface damage) with stiffness (resistance to bending) or toughness (resistance to breaking under impact).
Common phrases
surface hardness · hardness test · Rockwell hardness · hardness value · core hardness
The force that resists one surface sliding or rolling over another. It causes heat and wear, but it is also needed, for example in brakes and bolted joints.
Where you use it
Used in machine design, tribology and maintenance. Engineers reduce friction with lubrication and bearings and use the coefficient of friction (μ) in calculations. Static friction acts before movement starts, kinetic friction during movement.
Examples
We used a coefficient of friction of 0.15 in the bolted joint calculation.
Too much friction in the guide rails was making the slide stick.
Common phrases
coefficient of friction · reduce friction · friction loss · static friction · friction force
How much a part or structure resists bending, stretching or twisting under load. A stiff part deflects only a little; a flexible one deflects a lot.
Where you use it
Used for machine frames, shafts, brackets and in FEA. Stiffness depends on both the material (its modulus of elasticity) and the shape. Engineers add ribs or change the section to increase it. It is given in N/mm or N·m/rad.
Examples
Adding two ribs doubled the stiffness of the bracket without adding much weight.
The machine frame needs high stiffness to keep the cutting tool accurate.
Usage note
Stiffness is not strength: a part can be stiff but brittle, or strong but flexible. The adjective is stiff.
Common phrases
high stiffness · increase stiffness · torsional stiffness · bending stiffness · stiffness-to-weight ratio
Able to stretch and bend a lot before breaking. Most steels, copper and aluminum are ductile; glass and gray cast iron are not.
Where you use it
Used in materials science, failure analysis and design. Ductile materials give a warning by deforming before they fail, while brittle materials break suddenly. Engineers describe a ductile fracture or ductile behavior and measure ductility as elongation in a tensile test.
Examples
The fracture surface shows that the bolt failed in a ductile way, probably from overload.
Many steels become less ductile at very low temperatures.
Usage note
Ductile iron is a cast iron with round graphite particles; in Turkish it is 'küresel grafitli dökme demir' or 'sfero döküm'.
Common phrases
ductile material · ductile fracture · ductile iron · ductile behavior
A metal made by mixing a base metal with other elements to improve properties such as strength, hardness or corrosion resistance. Steel and brass are alloys.
Where you use it
Used in material selection, on drawings and in purchasing. An alloy is specified by its standard grade, for example 6061-T6 aluminum or 42CrMo4 steel. Alloy steel contains extra elements such as chromium or nickel.
Examples
We changed the housing from cast iron to an aluminum alloy to save weight.
This alloy has good corrosion resistance, but it is difficult to weld.
A long, round rotating part that carries gears, pulleys or wheels and transmits power and torque from one component to another.
Where you use it
Used in design, machining and maintenance. A shaft is supported by bearings, connected with couplings and has features such as shoulders, keyways and splines. Common phrases: drive shaft, output shaft, shaft diameter.
Examples
The output shaft is supported by two deep groove ball bearings.
We found wear marks on the shaft where the seal runs.
Usage note
An axle is mainly the part that wheels turn on or are fixed to; shaft is the general word for a rotating part that transmits torque. Turkish 'aks' is axle, not shaft.
A machine element that supports a rotating or sliding part, such as a shaft, and reduces friction between the moving surfaces. Ball and roller bearings are the most common types.
Where you use it
One of the most common words in machine design and maintenance. Bearings are selected, mounted, lubricated and replaced; engineers talk about bearing life, load rating and bearing failure. Rolling bearings are rulman in Turkish, plain bearings are kaymalı yatak or burç.
Examples
The noise is coming from the motor bearing on the non-drive end.
We replaced both bearings and checked the shaft for wear.
Usage note
In maintenance, DE (drive end) and NDE (non-drive end) tell you which bearing of a motor or pump is meant.
Common phrases
ball bearing · roller bearing · replace a bearing · bearing housing · bearing life
A toothed wheel that meshes with another toothed wheel to transmit rotation and torque, often changing speed or direction at the same time.
Where you use it
Used in machine design, gearboxes and maintenance. Gears mesh with each other; engineers talk about the gear ratio, the module, backlash and tooth wear. The main types are spur, helical, bevel and worm gears.
Examples
The small gear has 18 teeth and the large one has 54, so the gear ratio is 3:1.
Helical gears run more quietly than spur gears at high speed.
Usage note
Gear can also mean equipment ('safety gear') and, in cars, a gear position ('change gear'). In a machine design text it almost always means the toothed wheel.
Common phrases
gear ratio · spur gear · helical gear · gear teeth · mesh with
Any small part used to join two or more parts together, such as a bolt, screw, nut, washer, rivet or pin.
Where you use it
Used on drawings, in bills of materials, purchasing and assembly instructions. Engineers specify the fastener size, grade and coating; quality teams report loose or missing fasteners. It is mostly used in the plural.
Examples
All fasteners must be stainless steel because the unit is installed outdoors.
During the audit we found two loose fasteners on the machine guard.
A threaded metal fastener with a head, used with a nut or a threaded hole to clamp parts together. It is described by its diameter, length, thread and strength class.
Where you use it
Used in assembly, design and maintenance. Bolts are tightened, torqued, loosened and replaced. A metric bolt is written like M12 × 40, 8.8 (diameter, length, property class). Common types are hex bolts, socket head cap screws and anchor bolts.
Examples
Use M10 bolts, class 8.8, with washers on both sides.
One of the mounting bolts had come loose, and that was causing the vibration.
Usage note
Strictly, a bolt goes through the parts and takes a nut, while a screw goes into a threaded hole. Turkish speakers often call both 'vida', but the difference matters on English drawings and orders.
An elastic machine element that stores energy when it is compressed, stretched or twisted and pushes back when released. Most are made of coiled spring steel wire.
Where you use it
Used in machine design, valves, vehicles and mechanisms. The main types are compression, extension (tension) and torsion springs. Engineers specify the spring rate (force per unit of deflection), the free length and the wire diameter.
Examples
The valve is held closed by a compression spring with a rate of 15 N/mm.
Replace the return spring if it has lost its tension.
Common phrases
compression spring · spring rate · spring force · return spring · spring steel
A device that connects two shafts, for example a motor and a pump, so that torque is transmitted between them. Flexible types also allow a small amount of misalignment.
Where you use it
Used in machine design, installation and maintenance. Couplings are rigid or flexible; common types include jaw, gear, disc and grid couplings. Technicians check coupling alignment and replace worn rubber elements.
Examples
Check the alignment of the coupling between the motor and the pump after installation.
The rubber insert in the coupling was cracked, so we replaced it.
Usage note
Do not translate kaplin as 'clutch'. A clutch (kavrama, debriyaj) can connect and disconnect shafts during operation; a coupling keeps them connected.
A part that stops liquid, gas or dirt from leaking between two surfaces, especially where one part moves, such as a rotating shaft or a sliding piston rod.
Where you use it
Used for pumps, gearboxes, hydraulics and pneumatics. Common types are lip seals (oil seals), O-rings and mechanical seals. Seals leak, wear and are replaced, and their material is chosen for the fluid and temperature. It is also a verb: to seal a joint.
Examples
The mechanical seal on pump 3 is leaking and needs to be replaced.
Use an FKM seal because the oil temperature is above 120 °C.
Common phrases
oil seal · mechanical seal · shaft seal · seal leak · replace the seal
A closed unit of gears, shafts and bearings in a housing that changes the speed and torque between a motor and the machine it drives.
Where you use it
Used in industrial drives, conveyors, vehicles and wind turbines. A gearbox has a ratio, a rated torque and a specified oil type and level. Technicians check the oil, listen for noise and look for leaks. A gearbox that lowers the speed is also called a speed reducer.
Examples
The conveyor is driven by a 4 kW motor through a 25:1 gearbox.
Change the gearbox oil after the first 500 hours of operation.
Usage note
In Turkish, an industrial gearbox is usually 'redüktör' and a vehicle gearbox is 'şanzıman'. In American English a car gearbox is usually called a transmission.
A flat sealing piece placed between two fixed surfaces, such as pipe flanges or a cover and a housing, to stop leaks when they are bolted together.
Where you use it
Used in piping, engines, pumps and pressure equipment. Gaskets are made of rubber, fiber, graphite or metal and are normally replaced whenever a joint is opened. Engineers choose the gasket material and specify the bolt torque needed to compress it.
Examples
Always fit a new gasket when you reassemble the flange.
The leak was caused by a damaged gasket on the pump cover.
Usage note
A gasket seals between surfaces that do not move (conta); a seal is often used where a part moves, such as a rotating shaft (keçe).
Common phrases
flange gasket · replace the gasket · gasket material · head gasket · rubber gasket
A slot cut along a shaft or inside a hub into which a key fits, so that a gear, pulley or coupling turns together with the shaft.
Where you use it
Used in shaft design, machining and assembly. Keyways are milled in shafts and broached or slotted in hubs, and their sizes follow standards such as DIN 6885. A keyway weakens the shaft and creates a stress concentration, which designers must take into account.
Examples
The key was loose in the keyway, so the pulley was slipping.
The fatigue crack started at the end of the keyway.
Usage note
The key is the part itself (kama); the keyway is the slot it sits in. Do not use keyway for the key.
Common phrases
shaft keyway · parallel key · keyway dimensions · cut a keyway · key and keyway
To turn a bolt, nut or screw so that it holds parts together more firmly, often up to a specified torque. The opposite is loosen.
Where you use it
Used in assembly instructions, maintenance procedures and on the shop floor. Bolts are tightened to a torque and in a sequence, for example in a cross pattern, and care is taken not to over-tighten them. A drawing note may say 'tighten to 25 N·m'.
Examples
Tighten the cylinder head bolts in three steps to the final torque.
Don't over-tighten the plastic cover, or the threads will strip.
Usage note
Turkish workshops often say 'torklamak'; in English say 'tighten to the specified torque' or simply 'torque the bolts'.
Common phrases
tighten to torque · tighten in a cross pattern · over-tighten · hand-tighten · re-tighten
The movement of thermal energy from a hotter place to a colder one. It happens in three ways: conduction, convection and radiation.
Where you use it
A core university subject and a daily topic in thermal design, HVAC and the cooling of machines and electronics. Engineers calculate the heat transfer rate in watts and try to increase it in heat exchangers or reduce it with insulation.
Examples
Adding fins increases the surface area and improves heat transfer.
Scale on the tubes is reducing heat transfer in the boiler.
Common phrases
heat transfer rate · heat transfer coefficient · improve heat transfer · heat transfer area
The ratio of useful output to input, usually given as a percentage. A pump with 75% efficiency turns three quarters of its input power into useful work.
Where you use it
Used for motors, pumps, fans, boilers, gearboxes and whole plants. Engineers calculate, improve and compare efficiency, often on an efficiency curve. Energy efficiency describes buildings and equipment that use less energy for the same job.
Examples
The new motor has an efficiency of 95%, compared with 89% for the old one.
We improved the efficiency of the pump system by replacing the throttling valve with speed control.
Usage note
In engineering Turkish efficiency is usually 'verim'. 'Verimlilik' often means productivity, which is a different word in English.
Common phrases
energy efficiency · thermal efficiency · improve efficiency · efficiency curve · high-efficiency motor
The branch of physics and engineering that studies heat, work and energy and how they change from one form to another, for example in engines, turbines and refrigerators.
Where you use it
A core course for every mechanical engineer and the basis of power plants, engines, HVAC and refrigeration. People refer to the first law (energy is conserved) and the second law (heat flows from hot to cold; entropy). It takes a singular verb: thermodynamics is.
Examples
According to the first law of thermodynamics, the energy entering the system equals the energy leaving it plus the change in stored energy.
Thermodynamics was the hardest course in my second year.
Common phrases
first law of thermodynamics · second law of thermodynamics · engineering thermodynamics · thermodynamic cycle
A device that transfers heat from one fluid to another without mixing them, for example from hot oil to cooling water through metal plates or tubes.
Where you use it
Used in HVAC, process plants, power plants and machine cooling. Common types are plate and shell-and-tube heat exchangers. Engineers size, clean and inspect them and watch for fouling, which reduces their performance.
Examples
The plate heat exchanger needs cleaning; the outlet temperature is five degrees higher than usual.
Hot water from the boiler passes through a heat exchanger to heat the building circuit.
The increase in size of a material when its temperature rises. Each material expands by a different amount, given by its coefficient of thermal expansion.
Where you use it
Used in the design of pipes, engines, molds and precision parts. Engineers allow for thermal expansion with gaps, expansion joints or sliding supports. Steel expands about 12 µm per meter for each °C, aluminum about twice as much.
Examples
The steam line needs an expansion loop to take up the thermal expansion between cold and operating conditions.
We measure precision parts at 20 °C so that thermal expansion does not affect the results.
Usage note
Coefficient of thermal expansion is often shortened to CTE.
Common phrases
coefficient of thermal expansion · allow for thermal expansion · expansion joint · thermal growth
Heat transfer between a surface and a moving fluid such as air or water, or within the fluid as it flows. It can be natural, or forced by a fan or pump.
Where you use it
Used in heat transfer calculations, HVAC and electronics cooling. Natural (free) convection happens because warm fluid rises; forced convection uses a fan or pump. Engineers use the convection heat transfer coefficient h, in W/(m²·K).
Examples
Natural convection is not enough to cool the cabinet, so we added a fan.
Forced convection over the fins removes most of the heat from the motor.
A material property that shows how easily heat passes through a material by conduction, measured in W/(m·K). Copper conducts heat very well; insulation foam does not.
Where you use it
Used in material selection, heat sink design, insulation and heat transfer calculations. It is written with the symbol k or λ (lambda). Engineers choose high-conductivity materials for heat sinks and low-conductivity materials for insulation.
Examples
Aluminum is used for heat sinks because of its high thermal conductivity and low weight.
The insulation has a thermal conductivity of 0.035 W/(m·K).
Common phrases
high thermal conductivity · low thermal conductivity · thermal conductivity value · thermal resistance
A closed vessel in which water is heated by burning fuel or by electricity, to produce hot water or steam for heating buildings or for industrial processes.
Where you use it
Used in building services, power plants and industry. Boilers are fired, started, shut down and inspected. Common types are hot water, steam, fire-tube and water-tube boilers; condensing boilers recover heat from the flue gas. As pressure equipment, boilers need regular safety inspections.
Examples
The steam boiler produces 5 tons of steam per hour at 10 bar.
We replaced the old boiler with two condensing units to improve efficiency.
Usage note
A combi boiler (kombi) heats both the central heating water and the tap water. A boiler room is a kazan dairesi.
Common phrases
steam boiler · condensing boiler · boiler room · boiler efficiency · hot water boiler
The amount of heat needed to raise the temperature of 1 kg of a material by 1 °C (1 K). Water has a high value, about 4.18 kJ/(kg·K).
Where you use it
Used in heat balance, HVAC and process calculations, and usually written c or cp. Engineers use Q = m · c · ΔT to find the heat needed to warm or cool a fluid. The full name is specific heat capacity.
Examples
Because water has a high specific heat, it is a good fluid for carrying heat in heating systems.
Use the specific heat of the oil, not of water, in this calculation.
Common phrases
specific heat capacity · specific heat of water · cp value · heat balance
The force with which a liquid or gas pushes on each unit of area. It is measured in pascals, bar or psi.
Where you use it
Used constantly with pumps, compressors, piping, hydraulics and HVAC. Pressure rises, drops, builds up and is relieved; it is read on a pressure gauge. Gauge pressure is measured relative to the atmosphere, absolute pressure relative to a vacuum.
Examples
The system pressure dropped from 6 bar to 4 bar when the second line was opened.
Check the pressure on the gauge before you open the valve.
Usage note
Psig and psia mean gauge and absolute pressure in psi. Writing only 'bar' can be unclear, so many datasheets write 'barg' or 'bar(g)' for gauge pressure.
Common phrases
operating pressure · pressure gauge · pressure relief valve · high pressure · pressure test
The amount of fluid that passes a point in a given time, given as a volume (for example m³/h or L/min) or as a mass (kg/s).
Where you use it
Used for pumps, fans, pipes and HVAC systems. Engineers measure, set and adjust the flow rate and read it from a flow meter. A pump curve shows head against flow rate. Calculations separate volumetric and mass flow rate.
Examples
The pump delivers a flow rate of 40 m³/h at 30 m head.
The cooling water flow rate is too low, so the oil temperature keeps rising.
Usage note
Flow rate is an amount per time (debi); flow velocity is a speed in m/s (akış hızı). Translating debi as 'flow speed' is a common mistake.
Common phrases
volumetric flow rate · mass flow rate · design flow rate · measure the flow rate · flow meter
A machine that moves liquid through pipes by adding energy to it, raising its pressure or lifting it to a higher level.
Where you use it
Used in plants, buildings and machines. A pump is started, stopped, primed and sized; engineers read its pump curve and watch for cavitation. Common types are centrifugal and positive displacement pumps. It is also a verb: to pump water.
Examples
The pump is making a rattling noise, which may be a sign of cavitation.
We need a centrifugal pump that can deliver 25 m³/h at 4 bar.
Common phrases
centrifugal pump · pump curve · start the pump · pump seal · pump capacity
A device that starts, stops or controls the flow of a liquid or gas in a pipe by opening, closing or partly blocking the passage.
Where you use it
Used everywhere in piping, HVAC, hydraulics and process plants. Valves are opened, closed and throttled. Common types are ball, gate, globe, butterfly, check and pressure relief valves. A control valve is moved automatically by an actuator.
Examples
Close the isolation valves on both sides before you remove the pump.
A check valve on the discharge line stops the water from flowing back.
Usage note
Turkish says vana for pipeline valves, valf for hydraulic and pneumatic valves and supap for engine valves. English uses valve for all of them.
Common phrases
ball valve · check valve · isolation valve · control valve · open the valve
A machine that increases the pressure of a gas, such as air or a refrigerant, by reducing its volume. It is driven by an electric motor or an engine.
Where you use it
Used in compressed air systems, refrigeration, HVAC and gas plants. Common types are screw, reciprocating (piston), scroll and centrifugal compressors. People talk about a compressor's capacity, discharge pressure, load and unload cycles and energy use.
Examples
The screw compressor supplies compressed air to the whole plant at 7 bar.
Leaks in the air lines make the compressor run much longer than necessary.
Common phrases
air compressor · screw compressor · compressed air · compressor capacity · discharge pressure
A measure of how thick a fluid is and how strongly it resists flowing. Honey has a high viscosity and water has a low one.
Where you use it
Used for oils, hydraulic fluids and lubricants and in pump and pipe calculations. Viscosity falls as temperature rises. Oils are specified by viscosity grade, such as ISO VG 46. Dynamic viscosity is given in Pa·s and kinematic viscosity in mm²/s (cSt).
Examples
In winter the oil viscosity is too high, and the hydraulic system responds slowly until it warms up.
Use an oil with a viscosity grade of ISO VG 68 for this gearbox.
The loss of pressure as a fluid flows through a pipe, filter, valve or other component, caused by friction and by changes in direction or cross-section.
Where you use it
Used in pump and fan selection, pipe and duct design and filter maintenance. Engineers calculate the pressure drop of a system to size pumps and fans; a rising pressure drop across a filter shows that it is getting clogged.
Examples
The pressure drop across the filter has reached 250 Pa, so it's time to replace it.
A larger pipe diameter will reduce the pressure drop and the pump energy.
Common phrases
pressure drop across · calculate the pressure drop · high pressure drop · pressure loss · differential pressure
Fluid flow in which the particles move in irregular, mixing paths. It happens at higher speeds and is the opposite of smooth, layered laminar flow.
Where you use it
Used in fluid mechanics, pipe and duct design and CFD. The Reynolds number tells whether flow is laminar or turbulent: in pipes, flow is usually laminar below about 2,300 and turbulent above about 4,000. Turbulent flow increases both heat transfer and pressure drop.
Examples
At this velocity the Reynolds number is about 50,000, so we have fully turbulent flow.
Turbulent flow inside the tubes improves heat transfer in the exchanger.
Common phrases
laminar flow · Reynolds number · fully turbulent · turbulence model
Short for computational fluid dynamics: computer simulation of how liquids and gases flow, together with the pressure, temperature and heat transfer that come with the flow.
Where you use it
Used for pumps, fans, valves, HVAC spaces, heat exchangers and vehicle aerodynamics. Engineers build a mesh, choose a turbulence model, set boundary conditions and run the simulation. Common tools include ANSYS Fluent and OpenFOAM. Said letter by letter.
Examples
The CFD results show a dead zone behind the baffle where the air hardly moves.
We ran a CFD simulation to check the pressure drop through the new valve.
Shaping a part by cutting away material with tools, for example by turning, milling, drilling or grinding, usually on a lathe or a CNC machine.
Where you use it
Used in manufacturing, quoting and design reviews. Parts are machined from bar stock, castings or forgings; engineers talk about machining time, machining cost and machining allowance. A workshop that does this work is a machine shop.
Examples
Machining this housing from solid aluminum takes about 40 minutes per part.
Joining metal parts permanently by melting them at the joint, often with a filler metal, so that they become one piece when they cool.
Where you use it
Used in fabrication, steel structures, piping and repair. Common processes are MIG/MAG, TIG, stick and spot welding. The verb is weld, and a weld is the joint itself. A WPS (welding procedure specification) describes exactly how a weld must be made.
Examples
TIG welding gives a cleaner finish on thin stainless steel.
After welding, the frame must be stress-relieved and checked for distortion.
Usage note
In Turkish workshops 'argon kaynağı' usually means TIG and 'gazaltı kaynağı' means MIG/MAG. In English, use the process names.
A group of parts joined together to form a unit, or the process of putting parts together. A smaller unit inside it is called a subassembly.
Where you use it
Used in CAD, production and documentation. In CAD you build an assembly from part files; in the plant, parts go to the assembly line. Assembly drawings show how parts fit together, and assembly instructions give workers the order of work.
Examples
The gearbox assembly weighs about 85 kg, so use the crane.
When we checked the assembly in CAD, we found an interference between the bracket and the cover.
Usage note
The verb is assemble (monte etmek) and the opposite is disassemble (sökmek). Mount is used for fixing a unit in place: 'mount the motor on the base'.
Common phrases
assembly line · assembly drawing · subassembly · final assembly · assembly instructions
Short for computer numerical control: machine tools such as lathes, mills and routers whose movements are controlled by a program instead of by hand.
Where you use it
Said letter by letter. Used before other nouns: CNC machine, CNC lathe, CNC machining, CNC operator. Programs are written in G-code and are often generated by CAM software from the CAD model.
Examples
We can make these parts on our five-axis CNC machine in a single setup.
The CNC program has to be updated after the drawing change.
Making a part by pouring molten metal into a mold and letting it harden. The word also means a part made in this way.
Where you use it
Used in foundries, purchasing and design. Common processes are sand casting, die casting and investment casting. Engineers discuss casting defects such as porosity and shrinkage, draft angles, and machining a casting to its final size.
Examples
The pump housing is an iron casting that is machined on the flange faces.
X-ray inspection showed porosity in two of the aluminum castings.
Common phrases
sand casting · die casting · investment casting · casting defect · iron casting
Heating and cooling a metal part in a controlled way to change properties such as hardness, strength or ductility. Annealing, hardening and tempering are examples.
Where you use it
Used on drawings, in specifications and with heat treatment suppliers. Common processes are annealing, normalizing, quenching and tempering, case hardening and stress relieving. The drawing usually states the process and the required hardness.
Examples
After heat treatment, the gears are ground to their final size.
The parts cracked during heat treatment because of the sharp internal corners.
Common phrases
heat treatment process · after heat treatment · quenching and tempering · case hardening · stress relieving
A machining process in which a rotating cutting tool with several teeth removes material from a workpiece to make flat surfaces, slots, pockets and complex shapes.
Where you use it
Used in machine shops and CNC manufacturing. Parts are milled on a milling machine (a mill) or a machining center. Machinists talk about face milling, end milling, cutting speed, feed and depth of cut. In turning, by contrast, the workpiece rotates instead of the tool.
Examples
The pockets are finished by milling with a 10 mm end mill.
Milling the housing takes much longer than turning the shaft.
Common phrases
CNC milling · face milling · milling machine · end mill · milling cutter
Metal made into thin, flat sheets, usually less than about 6 mm thick, and the parts made from it by cutting, bending and joining.
Where you use it
Used for enclosures, panels, brackets, ducts and car bodies. Typical processes are laser cutting, punching, bending on a press brake and welding. Sheet metal parts are designed in CAD with a flat pattern, and the thickness and bend radius are specified.
Examples
The cover is made from 1.5 mm galvanized sheet metal.
Send the flat pattern to the sheet metal shop for laser cutting.
Usage note
In the US, sheet thickness is sometimes given as a gauge number (for example 16 gauge). A higher gauge number means a thinner sheet.
Common phrases
sheet metal part · sheet metal fabrication · bend radius · press brake · flat pattern
A process that makes plastic parts by injecting molten plastic under high pressure into a closed steel mold, where it cools and hardens.
Where you use it
Used for high-volume plastic parts such as housings, clips and caps. Engineers design parts with draft angles and even wall thickness, and discuss mold cost, cycle time and defects such as sink marks, flash and warpage.
Examples
Injection molding is only economical here if we make more than 10,000 parts a year.
Add a 1° draft to the walls so the part comes out of the injection molding tool easily.
Making parts by building them up layer by layer from a digital model, in plastic or metal. It is the industrial term for 3D printing.
Where you use it
Used for prototypes, jigs and fixtures, complex lightweight parts and small series. Common technologies are FDM, SLA, SLS and metal powder bed fusion. Engineers talk about build time, layer height, support structures and post-processing. Often shortened to AM.
Examples
Additive manufacturing let us combine six welded parts into one printed bracket.
Metal additive manufacturing is still too expensive for this volume.
Common phrases
metal additive manufacturing · 3D printing · build time · support structures · layer height
Making round holes in a workpiece with a rotating cutting tool called a drill or drill bit, on a drill press, on a CNC machine or by hand.
Where you use it
Used in machining and assembly. Holes are drilled and then often reamed for accuracy or tapped for threads. Machinists talk about drill size, pilot holes, through holes and blind holes. Deep, accurate holes may need special drilling methods.
Examples
Drilling and tapping the 24 holes takes longer than milling the whole face.
Use a pilot drill before drilling the 20 mm hole.
Common phrases
drilling machine · drill bit · pilot hole · through hole · blind hole
A precise drawing of a part or assembly that shows its shape, dimensions, tolerances, material and finish, so that it can be made and inspected.
Where you use it
Engineers usually just say 'the drawing'. A drawing is prepared, checked, released and revised; it has views, dimensions, notes and a title block with the part number, revision, scale and material. Engineering drawing means the same thing.
Examples
Please send me the latest revision of the technical drawing before you order the parts.
According to the technical drawing, the hole should be 12 mm, not 10.
The material and finish are given in the title block of the technical drawing.
Usage note
Turkey and most of Europe use first-angle projection, the US mostly third-angle. Always check the projection symbol before reading the views.
Common phrases
release a drawing · drawing revision · title block · assembly drawing · detail drawing
Short for computer-aided design: software used to create 3D models and 2D drawings of parts and assemblies, such as SolidWorks, CATIA, Siemens NX or AutoCAD.
Where you use it
Pronounced as one word, 'cad'. Used on its own and before other nouns: CAD model, CAD file, CAD software. Engineers model parts in CAD, export CAD files as STEP or STL and check designs in CAD reviews.
Examples
Can you send me the CAD model in STEP format?
I updated the bracket in CAD, but the drawing hasn't been revised yet.
Common phrases
CAD model · CAD file · CAD software · 3D CAD · CAD drawing
A document or list that states exactly what a product, material or process must do or meet, such as dimensions, performance, materials and standards.
Where you use it
Used in purchasing, design and quality. A product meets, complies with or deviates from a specification. People often shorten it to spec and say a part is 'in spec' or 'out of spec'. The plural can mean a product's technical data.
Examples
The customer's specification requires a surface hardness of at least 58 HRC.
These valves don't meet the pressure specification, so we can't install them.
Common phrases
technical specification · meet the specification · out of spec · customer specification · material specification
A view on a drawing that shows a part as if it were cut along a plane, so that inner features such as holes, grooves and walls can be seen clearly.
Where you use it
Used on drawings and in CAD. The cutting plane is shown with a line and arrows labeled A-A, and the cut surfaces are filled with hatching. A section view is added when hidden lines would make the drawing hard to read. Also called a cross-section.
Examples
Add a section view through the bearing seat so the machinist can see the groove.
Section view B-B shows the wall thickness of the casting.
A structured list of all the parts, materials and quantities needed to make a product or assembly, usually with part numbers and descriptions.
Where you use it
Used in design, purchasing, production planning and ERP systems. Usually shortened to BOM, said as one word or letter by letter. Engineers create, release and update the BOM; it can appear as a table on the assembly drawing or be exported from CAD.
Examples
Please check the bill of materials before we send it to purchasing.
The washer was missing from the bill of materials, so it was never ordered.
Common phrases
BOM · update the bill of materials · engineering BOM · multi-level BOM · BOM structure
A computer method that divides a part into many small elements, called a mesh, to calculate stress, deflection, temperature or vibration under given loads.
Where you use it
Used in design validation and usually shortened to FEA. Engineers build a mesh, apply loads and boundary conditions, run the analysis and check the results against hand calculations or tests. Common software includes ANSYS, Abaqus and the simulation tools inside CAD programs.
Examples
The finite element analysis shows a stress peak at the weld toe.
Refine the mesh around the hole and run the finite element analysis again.
Usage note
FEA results are only as good as the loads, boundary conditions and mesh behind them. Engineers often say 'garbage in, garbage out' about simulation.
Common phrases
FEA model · run an FEA · mesh · boundary conditions · FEA results
The allowed amount of variation in a dimension or property, for example ±0.05 mm. A part is acceptable if its measured value falls inside this range.
Where you use it
One of the most used words on the shop floor and in quality meetings. Parts are within or out of tolerance; a tolerance can be tight or loose. Engineers specify and hold tolerances, and tighter tolerances usually mean higher cost.
Examples
The bore diameter is 30 mm with a tolerance of plus 0.02, minus zero.
Three of the ten samples were out of tolerance on the hole position.
Can your shop hold a tolerance of ±0.01 mm on this length?
Usage note
English uses a decimal point: 0.05, not 0,05. ±0.05 is read 'plus or minus five hundredths' or 'plus or minus zero point zero five'.
Common phrases
tight tolerance · within tolerance · out of tolerance · hold a tolerance · tolerance band
A measurement of size or position on a part, such as a length, width, diameter or the distance between two holes, shown as a number on a drawing.
Where you use it
Used on drawings, in inspection and when quoting. Engineers add, check and measure dimensions; a critical dimension is one that affects function. As a verb, dimension means to put dimensions on a drawing. Overall dimensions give the outside size of a product.
Examples
Mark the critical dimensions on the drawing so the inspector checks them first.
The overall dimensions of the unit are 1200 × 800 × 950 mm.
The relationship between the sizes of two parts that go together, such as a shaft and a hole, which decides whether they slide freely or are pressed tightly together.
Where you use it
Used in design, drawings and assembly. There are clearance fits (there is always a gap), interference or press fits (the shaft is larger than the hole) and transition fits. ISO fits are written with codes such as H7/g6 or H7/p6.
Examples
The bearing has an interference fit on the shaft, so it has to be heated before mounting.
We changed the pin to a clearance fit because it was too hard to assemble.
Common phrases
clearance fit · interference fit · press fit · transition fit · H7/g6 fit
A hand measuring tool with two jaws that measures outside and inside sizes and depths, usually to 0.01 or 0.02 mm. It can be vernier, dial or digital.
Where you use it
Used every day on the shop floor and in quality control. People measure a part 'with a caliper' or 'with calipers'; both are common. For tighter tolerances a micrometer is used instead. The British spelling is calliper.
Examples
Measure the outside diameter with a digital caliper and write it on the check sheet.
The caliper reading was 24.96 mm, which is inside the tolerance.
Usage note
In the automotive world caliper also means a brake caliper. In measurement it is always kumpas.
Common phrases
digital caliper · vernier caliper · dial caliper · measure with a caliper
How smooth or rough a surface is after it has been made, usually given as a roughness value such as Ra 1.6 µm.
Where you use it
Used on drawings, in machining and in inspection. Engineers specify surface finish with a symbol on the drawing; machinists achieve it with the right tool, feed and speed. It is checked with a surface roughness tester.
Examples
The seal running surface needs a surface finish of Ra 0.4 µm or better.
Reduce the feed on the last pass to get a better surface finish.
Usage note
Surface finish (yüzey kalitesi) is different from surface treatment (yüzey işlemi), such as plating or anodizing, although some drawings use 'finish' for both.
Common phrases
surface finish requirement · smooth surface finish · surface roughness · Ra value · machined surface finish
Short for geometric dimensioning and tolerancing: a system of drawing symbols that controls the form, orientation, location and runout of features relative to datums.
Where you use it
Used on drawings, in inspection and in supplier communication. It is defined by ASME Y14.5 in the US and by ISO GPS standards in Europe. Engineers read feature control frames for flatness, perpendicularity, position and runout.
Examples
The customer drawing uses GD&T, so the hole positions are measured from datums A, B and C.
Our new engineers need GD&T training before they review supplier drawings.
Common phrases
GD&T symbols · GD&T training · feature control frame · position tolerance · flatness tolerance
A theoretically exact point, line or surface on a part, marked with a letter on the drawing, from which other features are located and measured.
Where you use it
Used with GD&T, in drawing checks and on the CMM. Datums are labeled A, B and C, and together they form a datum reference frame. Engineers choose datum features that match how the part is located in the assembly. In engineering the plural is datums, not data.
Examples
Datum A is the bottom face that sits on the base plate.
The inspector measured the hole positions from the wrong datum.
Common phrases
datum feature · datum reference frame · primary datum · datum surface
A calculation of how the tolerances of several parts add up in an assembly, to check that a gap, fit or position stays within its limits in the worst case or the typical case.
Where you use it
Used in design reviews, especially for assemblies with many parts. Engineers do a worst-case or a statistical (RSS) stack-up, often in a spreadsheet or with special software. The result shows which tolerances must be tightened and which can be relaxed.
Examples
The tolerance stack-up shows that the gap can drop to 0.1 mm in the worst case.
Before you tighten every tolerance on the drawing, do a proper tolerance stack-up.
A precision measuring tool with a calibrated screw that measures small sizes such as diameters and thicknesses, usually to 0.01 mm or 0.001 mm.
Where you use it
Used in machine shops and quality labs for tolerances tighter than a caliper can handle. There are outside, inside and depth micrometers. Machinists say they 'mike' a part; the value is read on the sleeve and thimble scales or on a digital display.
Examples
Check the bearing seat diameter with a micrometer, not with a caliper.
The micrometer reading was 19.992 mm, which is within the h6 tolerance.
Usage note
The tool is stressed on the second syllable, 'my-KROM-i-ter'. The unit (one millionth of a meter) is stressed on the first, 'MY-kro-mee-ter', and is often called a micron. Turkish uses 'mikrometre' for both.
Maintenance done at planned intervals, such as lubricating, inspecting and replacing worn parts, to stop equipment from breaking down unexpectedly.
Where you use it
Used by maintenance teams and plant managers, often shortened to PM. A PM schedule lists tasks by operating hours or by calendar. It is contrasted with corrective maintenance (after a failure) and predictive maintenance (based on condition data).
Examples
Preventive maintenance on the compressors is done every 2,000 operating hours.
Since we started a preventive maintenance program, unplanned downtime has dropped by half.
Usage note
Preventative maintenance means the same and is also common.
Common phrases
preventive maintenance schedule · PM program · scheduled maintenance · carry out preventive maintenance
The state in which a part or machine can no longer do its job, for example because it has cracked, worn out, leaked or stopped working.
Where you use it
Used in design, testing and maintenance. Engineers investigate failures, identify the failure mode and write failure analysis reports. Parts fail by fatigue, wear, corrosion or overload. FMEA (failure mode and effects analysis) is a common method for studying possible failures.
Examples
The failure started at a small crack near the keyway.
Bearing failure is the most common cause of motor downtime in our plant.
Usage note
Turkish uses 'arıza' for machines that stop working and 'hasar' for damaged materials or parts; English uses failure for both. The verb is fail.
Common phrases
failure mode · failure analysis · bearing failure · premature failure · cause of failure
Putting oil or grease between moving surfaces, for example in bearings, gears and chains, to reduce friction, wear and heat.
Where you use it
A daily maintenance task and a key topic in reliability. Technicians follow a lubrication schedule that lists the points, lubricants, amounts and intervals. Poor lubrication (too little, too much or the wrong type) is one of the main causes of bearing failure.
Examples
Most of these bearing failures were caused by poor lubrication.
Check the lubrication points on the conveyor every week.
Usage note
The verb is lubricate and the substance is a lubricant. In everyday speech people also say 'grease the bearing' or 'oil the chain'.
The time when a machine or production line is not working because of a breakdown, maintenance, a changeover or a lack of material.
Where you use it
Used in maintenance, production and management reports. Downtime is planned or unplanned; teams track and reduce it, often in hours per month or as part of OEE. Managers want to know how much downtime a repair will cause.
Examples
Unplanned downtime on line 2 was 14 hours last month, mostly because of the hydraulic press.
We'll replace the gearbox during the weekend shutdown to avoid extra downtime.
To find the cause of a problem in a machine or system step by step and fix it, for example by checking signals, parts and settings one after another.
Where you use it
Used by maintenance technicians, service engineers and commissioning teams. You troubleshoot a machine, a fault or a system; the noun is troubleshooting. Manuals often include a troubleshooting table that lists symptoms, possible causes and actions.
Examples
We spent two hours troubleshooting the hydraulic unit before we found a blocked filter.
Check the troubleshooting section of the manual before you call the supplier.
Common phrases
troubleshoot a problem · troubleshooting guide · troubleshoot a fault · basic troubleshooting
A fast back-and-forth movement of a machine or structure. Too much of it can be a sign of a problem such as imbalance, misalignment or a damaged bearing.
Where you use it
Used in machine design, maintenance and condition monitoring. Vibration is measured in mm/s or g with sensors and analyzers and compared with alarm limits. Machines are isolated from it with rubber mounts and dampers.
Examples
Vibration on the fan bearing has doubled since last month, so we should plan a stop.
The vibration analysis showed imbalance in the impeller.
Slow damage to a metal caused by a chemical reaction with its environment, such as water, air or chemicals. Rust on steel is the most familiar example.
Where you use it
Used in design, maintenance and inspection. Engineers prevent corrosion with coatings, galvanizing, stainless steel or cathodic protection. Galvanic corrosion happens when two different metals touch in a wet environment. Corrosion resistance is a key material property.
Examples
Corrosion has reduced the wall thickness of the pipe from 6 mm to 3.5 mm.
Insulating washers were added between the steel bolts and the aluminum plate to prevent galvanic corrosion.
Usage note
Rust is the corrosion of iron and steel only. Aluminum and copper corrode, but they do not rust.
Regularly measuring signs of a machine's health, such as vibration, temperature or oil quality, to spot problems early and plan repairs before a breakdown.
Where you use it
Used in maintenance and reliability engineering. Common techniques are vibration analysis, infrared thermography, oil analysis and ultrasound. Condition monitoring is the basis of predictive maintenance, where work is done when the data shows it is needed.
Examples
Our condition monitoring system sends an alarm when the bearing temperature goes above 85 °C.
Online condition monitoring was installed on the main compressors last year.
Short for mean time between failures: the average operating time between one failure of a repairable machine and the next. A higher MTBF means more reliable equipment.
Where you use it
Used in reliability reports, maintenance KPIs and supplier datasheets. It is calculated as total operating time divided by the number of failures. It often appears with MTTR (mean time to repair); for parts that are replaced rather than repaired, MTTF is used.
Examples
After the redesign, the MTBF of the packaging machine went up from 120 to 310 hours.
We track MTBF and MTTR for every critical machine each month.
Usage note
MTBF is an average, not a guarantee: a machine with an MTBF of 1,000 hours can still fail after 50 hours.
Common phrases
MTBF and MTTR · increase MTBF · MTBF value · reliability data
The gradual loss of material from a surface caused by friction, rubbing or hard particles during use, for example on bearings, gears, seals and cutting tools.
Where you use it
Used in maintenance, design and failure analysis. Parts show wear, wear marks or signs of wear; wear parts are designed to be replaced regularly. Engineers talk about wear resistance and about abrasive or adhesive wear. Wear and tear means normal damage from use.
Examples
There is heavy wear on the gear teeth, so the gearbox needs to be opened.
Chain wear is now above 3%, so replace the chain and both sprockets.
Usage note
The verb forms are wear, wore, worn: 'the bushing has worn'. Wear out means to become unusable through use. Wear is pronounced like 'where'.
Common phrases
wear and tear · wear resistance · signs of wear · wear part · excessive wear
To stop working because of a fault. It is used for machines and vehicles; the noun breakdown means a failure that stops the equipment.
Where you use it
Very common in everyday maintenance talk, reports and shift handovers. Machines break down, and teams respond to breakdowns and try to prevent them. The noun is one word (breakdown), the verb two (break down). Breakdown maintenance means repairing only after a failure.
Examples
Line 3 breaks down almost every week because of the same valve.
The breakdown of the main pump stopped production for six hours.
If the compressor breaks down at night, call the on-call technician.
Usage note
The past tense is broke down, and in this meaning there is no object: say 'the machine broke down', not 'we broke down the machine'. With an object, break down usually means something else, such as dividing costs into items.
A complete inspection and repair of a machine in which it is taken apart, cleaned and checked, and worn parts are replaced, so that it works almost like new.
Where you use it
Used for engines, pumps, compressors, gearboxes and turbines. An overhaul is planned and usually done after a set number of operating hours. It is also a verb: to overhaul a compressor. A major overhaul is much bigger than routine maintenance.
Examples
The turbine is due for a major overhaul after 40,000 operating hours.
We overhauled the gearbox and replaced all the bearings and seals.
Usage note
Turkish 'revizyon' is a natural translation here, but English 'revision' means a changed version of a document or drawing, not a machine overhaul.
Common phrases
major overhaul · complete overhaul · engine overhaul · overhaul interval · carry out an overhaul
A replacement part kept in stock so that a worn or broken part can be changed quickly, for example a bearing, seal, belt or motor.
Where you use it
Used in maintenance, purchasing and after-sales service. Plants keep a list of critical spare parts with minimum stock levels, and suppliers quote a lead time for each spare part. People often just say spares.
Examples
Make sure the critical spare parts are in stock before the shutdown.
This spare part has a lead time of eight weeks, so we need to order it now.
Common phrases
critical spare parts · spare parts list · spare parts stock · order a spare part · recommended spares
A condition in which two connected shafts, for example of a motor and a pump, do not share the same center line, either because they are offset or because they are at an angle.
Where you use it
Used in the installation and maintenance of rotating machines. Misalignment causes vibration, heat and early bearing and coupling failure. Technicians measure and correct it with dial indicators or laser alignment tools, adding shims under the motor feet.
Examples
The vibration spectrum points to misalignment between the motor and the gearbox.
After laser alignment, the misalignment was below 0.05 mm.
Short for heating, ventilation and air conditioning: the systems that control temperature, humidity and air quality in buildings, vehicles and industrial spaces.
Where you use it
Usually pronounced 'H-vac'. Used on its own and before other nouns: HVAC system, HVAC engineer, HVAC design. In building projects HVAC is part of MEP (mechanical, electrical and plumbing). HVAC&R also covers refrigeration.
Examples
The HVAC system must keep the cleanroom at 21 °C and 45% relative humidity.
I work as an HVAC engineer on hospital and office projects.
Usage note
Because it is read 'H-vac', write 'an HVAC engineer', not 'a HVAC engineer'.
A refrigeration machine that cools water or a water-glycol mixture, which is then pumped to air handling units, fan coils or process equipment.
Where you use it
Used in large buildings, hospitals, data centers and factories. Chillers are air-cooled or water-cooled (with a cooling tower). Engineers talk about chilled water supply and return temperatures, capacity in kW or tons and efficiency values such as EER or COP.
Examples
The chiller supplies water at 7 °C and gets it back at 12 °C.
We need a second chiller for redundancy in the data center.
A large HVAC unit that filters, heats or cools, sometimes humidifies, and moves air through a building's ductwork, using fans, filters, coils and dampers.
Where you use it
Used in commercial buildings, hospitals and cleanrooms, and usually shortened to AHU. Engineers specify the airflow, coil capacities and filter classes; technicians change filters and check belts and fans. A unit that handles only outside air is called a fresh air unit.
Examples
The air handling unit on the roof supplies 12,000 m³/h to the office floors.
Replace the bag filters in the air handling unit when the pressure drop reaches the limit.
Common phrases
AHU · supply air · return air · AHU filter · rooftop unit
The system of metal or plastic ducts that carries air from fans and air handling units to rooms and back, including bends, branches, dampers and grilles.
Where you use it
Used in HVAC design, installation and maintenance. Engineers size ductwork for air velocity and pressure drop; contractors install and insulate it. Most ductwork is galvanized sheet metal, rectangular or round. Ductwork is uncountable; for one piece, say a duct.
Examples
The ductwork above the ceiling is undersized, which makes the system noisy.
All supply ductwork must be insulated to prevent condensation.
The working fluid in a refrigeration or air conditioning system. It absorbs heat when it evaporates and releases heat when it condenses; R-32 and R-134a are examples.
Where you use it
Used in HVAC, refrigeration and heat pump work. Technicians charge, recover and check refrigerant and look for leaks. Refrigerants are compared by their GWP (global warming potential), and regulations are phasing out high-GWP types.
Examples
The unit lost most of its refrigerant through a leak at a brazed joint.
The new heat pumps use R-290, a natural refrigerant with a very low GWP.
Usage note
Turkish service teams often just say 'gaz', for example 'gaz basmak' for charging. In English, say refrigerant, or 'charge the system'.
Supplying fresh outdoor air to a space and removing stale or polluted air, either naturally through openings or mechanically with fans.
Where you use it
Used in HVAC design, building regulations and workplace safety. Ventilation rates are calculated in m³/h per person or in air changes per hour (ACH). Mechanical ventilation can include heat recovery, and exhaust ventilation removes fumes from welding areas or kitchens.
Examples
The meeting rooms need ventilation of at least 36 m³/h per person.
Poor ventilation in the welding area led to complaints about fumes.
Common phrases
mechanical ventilation · natural ventilation · ventilation rate · air changes per hour · exhaust ventilation
The amount of heat that must be removed from a space to keep it at the design temperature and humidity. It comes from the sun, people, lights, equipment and outdoor air.
Where you use it
Used in HVAC design to size chillers, air handling units and air conditioners. Engineers carry out a cooling load calculation, often with software, and separate sensible from latent load. Results are given in kW, or in the US in tons of refrigeration (1 ton ≈ 3.5 kW).
Examples
The cooling load of the server room is about 40 kW, mostly from the equipment.
Large west-facing windows increase the cooling load in the afternoon.
A device that uses a refrigeration cycle to move heat from a cooler place, such as outdoor air or the ground, to a warmer place for heating, or the other way round for cooling.
Where you use it
Used in buildings and industry as an efficient alternative to boilers. Common types are air-source, ground-source and water-source heat pumps. Performance is given as COP (coefficient of performance): a COP of 3 means 3 kW of heat for 1 kW of electricity.
Examples
The air-source heat pump has a COP of about 3.5 at an outdoor temperature of 7 °C.
We are replacing the old gas boiler with a heat pump.
Usage note
COP can be greater than 1 because a heat pump moves heat instead of creating it, so do not describe it as 'efficiency over 100%'.
An early working version of a product, built to test the design, check fit and function, and find problems before production starts.
Where you use it
Used in product development. Teams build, test and improve prototypes; a prototype can be 3D printed, machined or made by hand. Engineers talk about the prototype phase and prototype parts before moving to pre-series and mass production.
Examples
The first prototype passed the drop test but failed the heat test.
We 3D printed a quick prototype to check how the handle feels in the hand.
Common phrases
build a prototype · first prototype · working prototype · rapid prototyping · prototype testing
Checking a part, product or machine against a drawing, specification or standard by looking at it, measuring it or testing it.
Where you use it
Used in quality, manufacturing and maintenance. Common types are incoming inspection (for supplier parts), in-process inspection, final inspection and first article inspection. Parts pass or fail inspection, and the results go into an inspection report.
Examples
All incoming castings go through visual and dimensional inspection.
The first article inspection report must be approved before series production starts.
Common phrases
final inspection · incoming inspection · visual inspection · inspection report · first article inspection
A test in which a standard sample is pulled until it breaks, to measure properties such as yield strength, tensile strength and elongation.
Where you use it
Used in materials labs, quality control and material certificates. It is carried out on a universal testing machine according to standards such as ISO 6892-1 or ASTM E8. The result is a stress-strain curve and a test report.
Examples
The tensile test results show a yield strength of 380 MPa and 24% elongation.
We cut three samples from the plate for a tensile test.
Usage note
Tensile strength (ultimate tensile strength, UTS) is the highest stress reached in the test; yield strength is where permanent deformation starts.
Common phrases
tensile test specimen · tensile test results · carry out a tensile test · tensile strength · elongation at break
Comparing a measuring instrument with a more accurate reference and adjusting or correcting it when needed, so that its readings can be trusted.
Where you use it
Used in quality systems, labs and maintenance. Instruments such as calipers, gauges, torque wrenches and sensors need regular calibration; each gets a calibration certificate and a due date. Results must be traceable to national standards. The verb is calibrate.
Examples
This torque wrench is out of calibration, so don't use it until it comes back from the lab.
The auditor asked to see the calibration records for all the measuring tools.
Common phrases
calibration certificate · calibration due date · out of calibration · calibration lab · calibration interval
A structured way of finding the basic reason why a failure or problem happened, so that the real cause can be removed and the problem does not come back.
Where you use it
Used in quality, maintenance and engineering after failures and customer complaints. Often shortened to RCA. Common tools are the 5 Whys and the fishbone (Ishikawa) diagram, and the results often go into an 8D report. Teams carry out or conduct a root cause analysis.
Examples
The root cause analysis showed that the bolts were never torqued, not that they were too weak.
Replacing the bearing is a quick fix; we still need a root cause analysis.
Common phrases
carry out a root cause analysis · 5 Whys · fishbone diagram · 8D report · corrective action
Methods of checking materials, welds and parts for cracks and other defects without damaging them, such as ultrasonic, radiographic, magnetic particle or dye penetrant tests.
Where you use it
Used for welds, castings, pressure equipment, aircraft parts and in maintenance. Usually shortened to NDT (also NDE or NDI). Each method has a code: UT, RT, MT, PT, VT. NDT personnel are certified to levels 1, 2 and 3 under standards such as ISO 9712.
Examples
All butt welds on the pressure vessel need 100% non-destructive testing.
Non-destructive testing found a small crack under the paint.
Usage note
The opposite is destructive testing, such as tensile or impact tests, where the sample is broken.
A setup of equipment, sensors and fixtures built to test a part, machine or system under controlled conditions, often in long durability or performance tests.
Where you use it
Used in R&D, product validation and quality labs. Engineers design, build and run test rigs, mount parts on the rig and log data such as load, speed, temperature and number of cycles. Also called a test bench or test stand.
Examples
The hinge has completed 50,000 cycles on the test rig without any cracks.
We built a simple test rig to measure the pump flow at different speeds.
Common phrases
endurance test rig · build a test rig · test bench · test stand · data logging
Ten questions from this glossary. Pick the right meaning for each term and see your score.
How to learn mechanical engineering vocabulary
Read real texts from the field: bearing and pump catalogs, product datasheets, maintenance manuals, test reports and the notes on technical drawings all use the vocabulary in its natural context.
Learn each term with the verbs and adjectives that go with it: not just 'tolerance' but 'tight tolerance', 'within tolerance' and 'out of tolerance'.
Say numbers and units out loud the way engineers do: 'twenty-five newton meters', 'plus or minus five hundredths of a millimeter', 'six bar'. Remember that English uses a decimal point, not a comma.
Keep a two-column list of words that look like Turkish but mean something different, such as stress (gerilme, not 'stres') and efficiency (verim).
Practice describing a part or a problem in a few short English sentences, the way you would in an email to a supplier or a maintenance report.
Frequently asked questions
How can I learn English for mechanical engineering?
Read real texts from the field and notice how the words are used: catalogs, datasheets, standards, test reports and drawing notes. Learn each term together with its usual partners (tighten a bolt, replace a bearing, out of tolerance) and use new words right away in your own emails, reports and meetings.
Which mechanical engineering terms should I learn first?
Start with the words you meet on every drawing and in every meeting: stress, load, torque, shaft, bearing, gear, bolt, tolerance, dimension, pressure, flow rate, machining, welding and maintenance. Then move on to materials, thermodynamics, HVAC and testing. The terms in this glossary follow the same order, from most to least essential.
Do engineers in English use metric or imperial units?
Most countries and international standards use metric (SI) units: millimeters, newtons, megapascals, bar and degrees Celsius. In the United States you will still see inches, pounds, psi and degrees Fahrenheit, especially in HVAC and older drawings, so it helps to recognize both and to always check the units on a drawing or datasheet.
Why do some drawings from the US look different from the ones I learned at university?
Turkey and most of Europe use first-angle projection and ISO drawing standards, while the United States mostly uses third-angle projection and ASME standards. The views are placed differently around the main view, so check the projection symbol in the title block before you read the views.
