A
ATC (Automatic Tool Changer)
A CNC mechanism that automatically selects and loads tools from a tool magazine during machining.
Axis (X, Y, Z, plus A/B/C)
Defined directions of movement on a machine. Example, for a milling machine:
- X = left–right
- Y = front–back
- Z = vertical
Rotary axes (A, B, C) rotate around X, Y, and Z respectively.
B
Bed (Lathe or Mill)
The main structural component providing rigidity and supporting slides, carriage, or table assemblies.
Bed Mill
A milling machine with a fixed bed and vertically moving spindle head. Offers improved rigidity for heavy cuts.
Ballscrew
Low-friction precision screw assembly used in CNC machines for accurate positioning.
C
CNC (Computer Numerical Control)
Digital control of machine movement using programmed instructions (G-code).
CNC Lathe
A lathe with servo-driven axes and programmed cutting cycles for turning, facing, threading, and boring.
CNC Milling
Machining using a digitally controlled milling machine, typically a VMC or 5-axis machining centre.
Centre Height
Distance from the spindle centreline to the top of the bed on a lathe.
Chuck
The workholding device on a lathe that grips the component. Types include manual scroll, independent jaw, and power chucks.
Collet
A high-accuracy workholding device for small cylindrical components or tools.
CSS (Constant Surface Speed)
A spindle control mode on lathes that adjusts speed automatically so surface cutting speed remains constant.
D
DRO (Digital Readout)
Electronic position display system used on manual machines for accurate X, Y, Z movement measurement.
Datum
The reference point from which all measurements or CNC coordinates are taken.
E
E-stop (Emergency Stop)
A safety function that immediately cuts power and stops machine motion.
F
Feedrate
The speed at which the cutting tool advances into the material.
Facing (Turning)
Machining the end of a component to create a flat surface perpendicular to the axis.
G
G-Code
The programming language used to control CNC machines. Examples include G00 (rapid), G01 (linear cut), G02/G03 (arcs).
Gap Bed Lathe
A lathe with a removable gap section allowing larger diameter components to be machined over the gap.
Guideways
Precision surfaces or rails that allow controlled movement of axes (e.g., dovetail, box-way, or linear rail systems).
H
Headstock (Lathe)
The fixed housing containing the spindle, drive system, and gears on a lathe.
Headrace / Toolhead (Mill)
The upper assembly of a milling machine containing the spindle and drive motor.
I
Incremental Mode (G91)
Programming mode where movements are relative to the current position.
K
Knee (Milling)
The vertically adjustable casting that supports the saddle and table on knee mills such as the Bridgeport Series 1.
L
Leadscrew
A screw used to drive manual axes. Less accurate than ballscrews but offers strong tactile feedback.
Live Centre
A rotating centre in the tailstock used to support long workpieces.
Locking Levers
Manual clamps that secure slides or tables in position during machining.
M
M-Code
Machine commands used to control non-movement functions such as spindle start, coolant, and tool changes.
Machining Centre
A CNC milling machine equipped with automatic tool changing and enclosed cutting environment (typically a VMC).
Mandrel / Arbor
A bar inserted in a workpiece for machining internal diameters or for supporting thin components.
N
Nose Radius (Tooling)
Radius at the tip of a turning insert that affects surface finish and cutting forces.
O
Offset (Tool or Work Offset)
A value applied in CNC programming to locate the position of tools (length/radius) or the workpiece (G54–G59).
P
Pitch
Distance between threads on a screwcut part or between balls on a ballscrew.
Power Feed
Motorised axis movement used on mills and lathes for consistent feedrate.
Q
Quill
The movable spindle sleeve on a manual milling machine used for drilling or precise vertical feed.
R
RPM (Revolutions per Minute)
Spindle rotational speed.
Runout
The amount of deviation from true rotation, affecting accuracy of spindles and toolholders.
S
Saddle
The assembly that supports the table (milling) or cross-slide (turning) and moves along guideways.
Spindle
The rotating shaft that holds the cutting tool (milling) or rotates the workpiece (turning).
Swing Over Bed
Maximum diameter of a component that can rotate over the lathe bed.
Swing Over Cross Slide
Largest diameter that can rotate above the cross slide.
Swing in Gap
Maximum diameter that can rotate in the gap when the gap section is removed.
T
Tailstock
A sliding assembly on a lathe supporting the end of long workpieces or holding drills.
Tapping
Creating internal threads using a tap.
Taper (Spindle)
The internal spindle geometry for mounting tooling.
Common tapers: R8 (Bridgeport), BT/ISO/HSK (VMCs).
Toolroom Mill / Lathe
A precision machine used for jig, fixture, and tooling work requiring high accuracy.
Toolpath
The programmed route the cutter follows on a CNC milling machine.
Turret (Lathe)
A rotating indexable toolholder used on CNC lathes for quick tool changes.
V
VMC (Vertical Machining Centre)
A CNC milling machine with vertically orientated spindle, automatic toolchanger, and fully programmable motion.
W
Workholding
Methods used to secure a workpiece (e.g., vices, chucks, clamps, collets, fixtures).
Work Zero / Part Datum (WCS – G54 etc.)
The reference point used for CNC programming and measurement on a part.
Z
Zero Return / Homing
The process of returning CNC axes to machine reference positions at start-up.
