Machining
The family of manufacturing processes that shape a part by removing material as chips with a cutting tool. It covers turning, milling, drilling, grinding and others.
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Machining glossary
128 terms of the trade explained plainly: processes, machines, tolerances, CNC programming, materials and safety. Type any word to filter instantly.
Processes
Chip removal
The basic principle of machining: the tool, harder than the workpiece, separates material in small pieces (chips) to reach the required shape and size.
Turning
A process in which the workpiece rotates on its axis while a fixed tool moves along it to remove material, producing surfaces of revolution such as cylinders, tapers and threads.
Milling
A process in which a rotating multi-edged tool (the cutter) removes material from a normally stationary workpiece, producing flats, slots, pockets and complex shapes.
Drilling
The operation that produces cylindrical holes by means of a rotating drill advancing axially into the workpiece.
Reaming
A finishing operation on already drilled holes, using a tool called a reamer, to achieve an accurate diameter and a good surface finish.
Threading
Producing internal threads (with a tap) or external threads (with a die or a lathe tool) for bolted joints.
Boring
Enlarging and finishing existing holes to tight diameter and concentricity tolerances, common on large parts.
Grinding
A finishing process that uses an abrasive wheel to reach very tight tolerances and fine surface finishes, above all on hardened parts.
Honing
Finishing of internal surfaces (bores) with abrasive stones that improve geometry and leave a cross-hatch pattern which retains lubricant.
Lapping
An extremely accurate finishing process that rubs the part against a tool charged with loose abrasive to achieve exceptional flatness and roughness.
Broaching
A process that pushes or pulls a toothed tool (the broach) through or along the part to generate internal or external profiles, such as keyways or splines, in a single pass.
EDM (electrical discharge machining)
Machining by electrical discharges that erodes conductive materials with no mechanical contact; ideal for complex shapes and very hard materials.
Wire EDM
A variant of EDM that uses a fine metal wire as the electrode to cut profiles with great accuracy.
Laser cutting
A thermal process that cuts sheet and profiles with a high energy density laser beam, with great accuracy and a small heat-affected zone.
Waterjet cutting
Cutting with a jet of water at very high pressure, sometimes carrying abrasive, which generates no heat and works on almost any material.
Plasma cutting
Cutting of conductive metals with a jet of ionised gas at high temperature; fast and economical at medium thicknesses.
Bar turning (Swiss machining)
Series production of small turned parts on automatic lathes, typical of fasteners and precision components.
Climb milling
A milling strategy in which the feed of the part runs with the rotation of the cutting edge; it reduces wear and improves finish on rigid machines.
Conventional milling
A strategy in which the cutting edge works against the feed of the part; it creates more rubbing but tolerates backlash.
Face milling
A milling or turning operation that produces a flat reference surface on the part.
Slotting and grooving
Machining of channels or slots, both on the lathe (grooves) and on the milling machine (keyways, open pockets).
Pocketing
Removing material from an internal cavity (a pocket) in a part by milling.
Facing
A turning operation that machines the front face of the part, perpendicular to the axis of rotation.
Cylindrical turning
A turning operation that reduces the outside diameter of the part along its axis.
Machines and tooling
Lathe
A machine tool that rotates the workpiece against a cutting tool to generate shapes of revolution.
Milling machine
A machine tool with a rotating tool (the cutter) that removes material from the part to create flats and shapes.
Machining centre
A CNC milling machine with an automatic tool changer, able to carry out several operations with no manual intervention.
CNC lathe
A lathe governed by numerical control that runs programs to produce turned parts with high repeatability.
Grinding machine
A machine that finishes surfaces with an abrasive wheel; surface, cylindrical and centreless types exist.
Drill press
A machine intended to produce holes with drills; column, radial or benchtop.
Horizontal boring mill
A large machine for machining precision holes and faces on bulky parts.
Milling cutter
A rotating cutting tool with several edges used in milling: face mills, end mills, slot cutters, ball nose and others.
Drill
A rotating cutting tool for making holes; the twist drill is the most common.
Insert
An interchangeable carbide tip that forms the cutting edge on turning and milling tools.
Tool holder
The element that grips the cutting tool and connects it to the spindle or to the turret of the machine.
Spindle
The rotating shaft of the machine that holds and turns the tool (milling machine) or the workpiece (lathe).
Turret
The indexing tool holder of a lathe that carries several tools and positions them as the program calls for them.
Dividing head
A milling machine accessory that rotates the part through exact angles to machine gears, polygons or equally spaced holes.
Tailstock
The part of a lathe that supports the free end of long workpieces to stop them deflecting.
Steady rest
An auxiliary lathe support that holds long, slender parts to reduce vibration and deflection.
Grinding wheel
The abrasive tool of a grinding machine, made of bonded grains that remove material as microchips.
Tap
A tool that generates internal threads in a previously drilled hole.
Reamer
A finishing tool that brings a drilled hole to its final diameter and surface finish.
Countersink
A tool that creates a conical or cylindrical recess at the mouth of a hole to seat screw heads.
Metrology and tolerances
Tolerance
The permissible variation of a dimension from its nominal value; it defines how far a part may deviate and still be acceptable.
Dimension
A measurement marked on a drawing that states a size of the part (length, diameter, angle).
Fit
The relationship between the tolerances of two mating parts (shaft and hole): it can be a clearance fit, an interference fit or a transition fit.
Vernier caliper
A measuring instrument that reads lengths, diameters and depths, usually with a resolution of 0.05 or 0.02 mm.
Micrometer
A precision instrument that measures small dimensions with a typical resolution of 0.01 mm by means of a micrometer screw.
Dial indicator
An instrument that measures small deviations by comparison, useful for checking run-out, flatness or parallelism.
Surface roughness
The fine irregularities of a surface; it is quantified with parameters such as Ra and defines the surface finish.
Ra
Arithmetic mean roughness: the most widely used parameter to express the finish of a machined surface, in microns.
Surface finish
The final quality of a surface in terms of roughness and appearance, resulting from the process and the cutting parameters.
Concentricity
The geometric condition in which the axes of two surfaces of revolution coincide.
Flatness
A geometric tolerance that limits how far a surface may deviate from a perfect plane.
Perpendicularity
A geometric tolerance that controls the right angle between two features of the part.
Parallelism
A geometric tolerance that limits the deviation between two surfaces or axes that are meant to be parallel.
GD&T
Geometric dimensioning and tolerancing: the system that defines the permissible form, orientation and position of the features of a part.
Go/no-go gauge
An inspection tool that quickly checks whether a dimension is within tolerance without giving the actual value.
Metrology
The science of measurement; on the shop floor, the dimensional and geometric inspection of manufactured parts.
CMM (coordinate measuring machine)
Equipment that measures points in space with a probe in order to verify complex geometries with great accuracy.
Nominal
The theoretical value of a dimension, the starting point from which tolerances are applied.
Interference fit
A fit in which the shaft is larger than the hole, so that the parts are joined by pressing.
CNC programming
CNC
Computer numerical control: the system that governs the movements of the machine tool from a program.
G-code
The programming language of CNC machines; its instructions (G0, G1, G2 and so on) define movements and machining functions.
M-code
The auxiliary functions of a CNC program (spindle start, coolant, tool change, end of program).
CAM
Computer-aided manufacturing: software that generates tool paths and the CNC program from the 3D model.
CAD
Computer-aided design: software used to create the drawings and 3D models of the parts.
Post-processor
The CAM module that translates tool paths into the specific G-code understood by each machine control.
Interpolation
The calculation the control performs to move several axes together in a coordinated way, describing lines (linear) or arcs (circular).
Work offset (part zero)
The coordinate origin the programmer sets on the part, and against which all the geometry of the program is defined.
Machine zero
The fixed reference point of the machine, established when homing the axes.
Tool offset
The value stored in the control (length and radius) that compensates for the actual dimensions of each tool.
Cutter radius compensation
The function that shifts the tool path by the radius of the tool so that the cutting edge follows the programmed contour.
Canned cycle
A predefined routine in the control (drilling, tapping, pocketing and so on) that simplifies the programming of repetitive operations.
Home position
A known position to which the machine returns in order to synchronise its coordinates.
Axes (X, Y, Z)
The directions of movement of the machine; 5-axis centres add two rotary axes to orient the tool or the part.
5-axis
Machining in which the tool is oriented in five degrees of freedom, allowing complex geometries in a single setup.
Simulation
Virtual verification of the CNC program before cutting metal, to detect collisions and errors.
Feedrate override
The control that adjusts, in real time, the percentage of the programmed feed during machining.
Workholding and fixturing
Chuck
The workholding system of a lathe that grips the part with jaws closing concentrically.
Vice
The workholding element of a milling machine that grips the part between two jaws, one fixed and one moving.
Fixturing
The set of tools and devices designed to hold and locate the part while it is machined.
Workholding
The way the part is fixed to the machine so that it does not move during cutting.
Collet
A cylindrical clamping system that grips bar stock or tools with great concentricity.
Clamps
Pieces that fix the part or the fixture to the machine table by means of bolts and T-slots.
Magnetic chuck
A magnetic clamping table, common in surface grinding of steel parts.
Live centre
A lathe centre mounted on bearings that turns with the part, supporting it without friction.
Keyway
A slot machined in a shaft or a bore to house a key that transmits torque.
Materials
Steel
An alloy of iron and carbon, the most common material in machining thanks to its balance of strength and cost.
Stainless steel
Steel alloyed with chromium that resists corrosion; harder to machine because of its toughness and its tendency to work harden.
Aluminium
A light, easily machined metal, widely used in aerospace, automotive and prototyping.
Brass
An alloy of copper and zinc, soft and with excellent machinability, typical of bar turning and plumbing fittings.
Cast iron
An iron alloy with a high carbon content, good for machine beds and parts that need to damp vibration.
Titanium
A light, very strong metal used in aerospace and medicine; hard to machine because of its low thermal conductivity.
Carbide
A tool material made of tungsten carbide and cobalt, very hard and wear resistant.
High-speed steel (HSS)
A tool steel that keeps its edge at high temperature; common in drills and cutters.
Machinability
How readily a material can be machined, in terms of cutting force, tool wear and surface finish.
Hardness
The resistance of a material to being scratched or indented; measured on scales such as Rockwell (HRC) or Brinell.
Toughness
The ability of a material to absorb energy and deform without breaking.
Heat treatment
A controlled heating and cooling process (hardening, tempering, annealing) that changes the properties of the metal.
Cutting parameters
Cutting speed
The speed at which the cutting edge travels over the surface of the part, in m/min; it governs tool life and surface finish.
Feed
The distance the tool advances per revolution or per tooth; it affects finish and cycle time.
Depth of cut
The thickness of material the tool removes on each pass.
RPM
Spindle revolutions per minute; calculated from the cutting speed and the diameter.
Chip
The portion of material removed by the tool; its shape and colour tell you about the quality of the cut.
Coolant
The fluid (soluble oil, neat oil) that cools and lubricates the cutting zone, flushes chips away and extends tool life.
Soluble cutting fluid
A water-miscible cutting fluid, the most common coolant in a machine shop.
Tool wear
The progressive deterioration of the cutting edge through friction and temperature, which forces regrinding or replacement.
Built-up edge
A build-up of workpiece material welded to the cutting edge, which spoils the finish; avoided with the right parameters and coolant.
Chatter
Unwanted oscillation between tool and workpiece that leaves marks and shortens tool life.
Pass
Each travel of the tool removing material; roughing passes and finishing passes are distinguished.
Roughing
The stage that removes most of the material quickly, leaving a stock allowance for finishing.
Finishing
The last stage of machining, which produces the final size and the required roughness.
Trade and safety
Engineering drawing
The technical document that defines the part with its dimensions, tolerances, materials and finishes.
Prototype
The first trial part made to validate the design before series production.
Production run
Repeated manufacture of the same part in quantity; it demands repeatability and process control.
Repeatability
The ability of the machine and the process to produce identical parts consistently.
Setup
Preparation of the machine, tools and fixturing before starting to machine a part or a batch.
PPE
Personal protective equipment (eye protection, gloves where appropriate, footwear, hearing protection) required in the workshop.
Burr
The ridge of material left on the edges after machining, which has to be removed.
Deburring
The operation of removing burrs and breaking sharp edges to leave the part safe and finished.
Quality control
Verification that parts meet the drawing and its tolerances before they are delivered.
Traceability
The record that allows the manufacturing history of a part or batch to be followed.
FP de Fabricación Mecánica
The Spanish vocational qualification in mechanical manufacturing that trains machinists; it includes the Machining certificate and the Production Programming certificate.
Fitter
An operator who specialises in manual fitting and precision assembly of machined parts.
Inspection
Checking with measuring instruments that the machined part meets the dimensions on the drawing.
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