Resources
Machining glossary
Definitions of the terms buyers and engineers meet when sourcing machined parts.
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Documented quality management system
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Calipers, micrometers, height gauge, DTIs
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VCI film, ISPM-15 wooden crates
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Terms
CNC Turning
A machining process in which the workpiece rotates while a stationary cutting tool removes material to create cylindrical features such as diameters, tapers, grooves and threads.
CNC Milling
A process in which a rotating multi-point cutter moves along programmed paths to remove material from a fixed workpiece, producing flats, pockets, slots and contours.
VMC (Vertical Machining Centre)
A CNC milling machine with a vertically oriented spindle and automatic tool changer, used for drilling, boring, tapping and milling in one set-up.
Tolerance
The permissible variation from a nominal dimension, for example Ø20 ±0.01 mm means any size from 19.99 to 20.01 mm is acceptable.
Runout (TIR)
Total Indicator Reading of how much a rotating surface deviates from true rotation about its axis, measured with a dial test indicator.
Surface Finish (Ra)
Ra is the arithmetic average roughness of a surface in micrometres (µm). Typical turned finishes range from Ra 3.2 to Ra 0.8 µm.
H7 Bore
An ISO 286 hole tolerance class widely used for bearing and dowel fits; for a Ø20 mm bore it allows 0 to +0.021 mm.
h6 / g6 Shaft Tolerance
ISO 286 shaft tolerance classes. h6 gives a close location fit; g6 gives a precise running clearance with an H7 hole.
Keyway
A slot machined in a shaft or hub that holds a key to transmit torque between them, commonly to DIN 6885 or ANSI B17.1.
PTFE
Polytetrafluoroethylene, a fluoropolymer known for chemical inertness, very low friction and service from −200 °C to +260 °C.
PEEK
Polyether ether ketone, a high-performance thermoplastic with continuous service to about 250 °C, high strength and excellent chemical resistance.
Delrin (Acetal, POM)
Polyoxymethylene, a stiff, low-friction engineering plastic with very low moisture absorption. Delrin is DuPont's homopolymer brand.
Nylon (Polyamide)
A tough engineering plastic family (PA6, PA66, cast nylon) with good wear and impact resistance.
SS 316 Stainless Steel
An austenitic stainless steel with added molybdenum for better resistance to chlorides and marine environments than SS 304.
Free-Cutting Brass
Brass alloys such as CZ121 / C36000 with lead or bismuth additions that break chips easily for very fast machining.
First Article Inspection (FAI)
Full dimensional inspection of the first part from a new set-up or production run against every drawing characteristic.
Material Test Certificate (MTC)
A mill certificate (typically EN 10204 3.1) stating the chemical composition and mechanical properties of a material heat.
ISO 9001:2015
The international standard for quality management systems, covering process control, documentation, corrective action and continual improvement.
AS9100
The aerospace quality management standard built on ISO 9001 with additional requirements for risk, configuration management and product safety.
FOB (Free On Board)
An Incoterm under which the seller delivers goods loaded on the vessel at the named port of shipment; risk passes to the buyer at that point.
CIF (Cost, Insurance and Freight)
An Incoterm under which the seller pays freight and minimum insurance to the named destination port; risk passes when goods are loaded at origin.
EXW (Ex Works)
An Incoterm under which the buyer collects goods at the seller's premises and handles export clearance and all transport.
ISPM-15
The international standard requiring wooden packaging used in trade to be heat-treated or fumigated and stamped with the IPPC mark.
VCI Packaging
Volatile Corrosion Inhibitor film or paper that releases a protective vapour around metal parts to prevent rust during transit.
HS Code
The Harmonized System number used worldwide to classify traded goods and decide import duty rates.
Certificate of Origin
A document certifying the country where goods were manufactured, required to claim free-trade-agreement duty benefits.
China+1
A sourcing strategy in which companies add suppliers outside China to reduce concentration risk, tariffs and lead-time exposure.
DFM (Design for Manufacture)
Reviewing a design to reduce manufacturing cost and risk, for example relaxing non-critical tolerances or standardising thread sizes.
STEP File
ISO 10303 neutral 3D CAD format (.step/.stp) readable by almost all CAD/CAM systems.
IGES File
An older neutral CAD exchange format (.igs/.iges) for surfaces and wireframe geometry.
Thread Classes (6g/6H)
ISO metric thread tolerance classes. 6g is the standard external thread class and 6H the standard internal class.
BSP vs NPT Threads
BSP (British Standard Pipe) has a 55° thread angle and is common in Europe and Asia; NPT (National Pipe Taper) has 60° and is standard in North America.
Passivation
A chemical treatment that removes free iron from stainless steel surfaces and strengthens the protective chromium oxide layer.
Anodising
An electrochemical process that thickens the oxide layer on aluminium for corrosion and wear resistance and allows colouring.
PPAP
Production Part Approval Process, an automotive framework of documents proving a supplier can consistently produce parts to specification.
Cpk (Process Capability)
A statistical index of how well a process stays centred within tolerance limits; Cpk ≥ 1.33 is a common target.
Height Gauge
A precision instrument used on a granite surface plate to measure heights, steps and hole positions.
Micrometer
A precision measuring instrument with resolution down to 0.001 mm, used to measure outside diameters and thicknesses.
Dial Test Indicator (DTI)
A lever-type gauge that measures small deviations such as runout, flatness and concentricity.
Granite Surface Plate
A flat, stable granite reference surface used as the datum for height gauges and other inspection set-ups.
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