How to Use This Guide
Our CNC machining glossary explains common manufacturing terms to help buyers understand drawings, specifications and production requirements.
Glossary
Machining Processes (10 terms)
CNC Machining
Computer-controlled machining that removes material from a solid block to create a part to a programmed shape. For buyers, it means custom parts made directly from your drawing or 3D model, with no tooling or moulds to pay for up front.
CNC Milling
A CNC process where rotating cutting tools remove material from a stationary workpiece. Milling handles flat surfaces, pockets, slots, threads and complex 3D shapes — the workhorse process for most custom metal parts.
CNC Turning
A CNC process where the workpiece rotates against a stationary cutting tool, used for cylindrical parts such as shafts, bushings and fittings. Turning produces round features with excellent concentricity in a single setup.
3-Axis Machining
The basic milling configuration, moving the tool along X, Y and Z axes. Suitable for flat or prismatic parts where the tool always approaches from above — the most economical option when geometry allows it.
4-Axis Machining
Adds rotation of the workpiece around one axis, letting the machine reach four sides without re-clamping. Used for parts with features on multiple faces where 3-axis would require extra setups.
5-Axis Machining
A configuration that rotates the workpiece around two additional axes, allowing the tool to approach from any direction. Required for impellers, complex housings and organic geometries; also improves accuracy by reducing re-clamping.
Swiss Machining
A precision turning method where the bar stock slides through a guide bushing while tools cut close to the bushing. Ideal for small, long, slender parts — think pins, small shafts and medical components held to very tight tolerances.
Drilling
Producing holes with a rotating drill bit. On CNC machines, drilling is done to programmed depth and position, and can be combined with reaming or boring when hole accuracy matters.
Tapping
Cutting internal threads in a pre-drilled hole. Tapped holes are common on machined parts; specifying thread depth and whether it is through or blind helps the shop avoid surprises in cost and lead time.
Boring
Enlarging an existing hole with a single-point tool to achieve accurate diameter, roundness and surface finish. Chosen when a drilled or reamed hole is not precise enough, such as bearing seats.
Glossary
Dimensions, Quality & Order Terms (19 terms)
Tolerance
The allowable variation in a dimension. In machining, tighter tolerances mean more careful setups, more inspection and higher cost — so specify only what your application truly needs.
Repeatability
The ability of a machine or process to produce the same result part after part. High repeatability is what makes production runs trustworthy once the first article is approved.
Accuracy
How close a machined feature is to the true programmed value. Accuracy depends on machine calibration and thermal stability; it is verified by measuring the finished part, not assumed.
Surface Finish
The texture left on a machined surface, usually specified as Ra. Finish affects sealing, friction, fatigue life and appearance — and finer finishes cost more, so match the requirement to the function.
Ra Value
The average roughness of a surface, measured in micrometres or microinches. A typical machined finish is Ra 1.6 µm; sealing faces or bearing surfaces may require Ra 0.8 or finer.
Chamfer
A bevel cut on an edge, typically 45°, specified to remove sharp corners. Chamfers protect the part during handling and make assembly easier; they are quick to add and should be on every drawing.
Fillet
A rounded internal corner where two surfaces meet. Fillets reduce stress concentration and are often required where a part is loaded; on the drawing they must specify the radius.
Undercut
A recess cut into a feature, such as a groove behind a thread or shoulder. Undercuts enable sealing (O-ring grooves) or assembly; they need a width and depth callout so the shop can select the right tool.
Datum
A reference point, line or plane from which dimensions and tolerances are measured. Correct datum selection on the drawing tells the machinist what to hold and how to set up the part.
Stock Allowance
The extra material left on a part between machining stages, or the material left for a finishing operation. On the drawing it affects roughing strategy, distortion control and cost.
Prototype
An initial part made to validate design, fit or function before production. Prototypes are typically machined in small quantities from the same material as production, with fast turnaround.
Low-Volume Production
Small production runs, commonly from a few pieces to a few hundred. CNC is ideal here because there are no moulds — we can machine 5 or 500 parts from the same program at similar unit economics per setup.
High-Volume Production
Larger production runs where per-piece cost becomes the focus. Process optimisation, fixturing and automation bring the unit price down; we quote high-volume jobs on their own merits.
First Article Inspection (FAI)
A full dimensional check of the first part against the drawing, documented before production continues. Buyers in aerospace, medical and automotive expect an FAI report with the first batch — we include it with every order.
CMM (Coordinate Measuring Machine)
A precision measurement machine that probes a finished part and compares its dimensions against the CAD model or drawing. CMM inspection is how we verify critical tolerances and issue a report with each shipment.
GD&T (Geometric Dimensioning & Tolerancing)
A symbolic language on drawings that defines geometry — flatness, position, roundness, profile — beyond simple size limits. It tells the machinist exactly what must be controlled and how it will be measured.
MOQ (Minimum Order Quantity)
The smallest order a supplier will accept. We work without a minimum order quantity: quantity affects unit price, not whether we will take the job — prototypes of one piece are welcome.
Lead Time
The time from order confirmation to shipment. Typical CNC lead times depend on material, complexity and quantity; we quote a realistic lead time with every price and communicate any change early.
Scrap / Rework
Parts that fail inspection and must be discarded (scrap) or corrected (rework). A good shop controls both through capable processes and thorough first-article inspection — the goal is zero scrap, not sorting it out later.
Glossary
Engineering & File Formats (7 terms)
CAD (Computer-Aided Design)
The digital model of your part, created in software such as SolidWorks, Fusion 360 or NX. For quoting and machining, a 3D CAD file plus a 2D drawing with tolerances is the ideal package.
CAM (Computer-Aided Manufacturing)
The software that converts a CAD model into machine toolpaths — deciding how the cutter moves, how fast, and in what order. Good CAM programming is where machining quality and cost are largely decided.
STEP
The most common neutral 3D file format for exchanging CAD models between different software. If you can only send one file, a STEP (.stp) model is what most machine shops prefer for programming.
DXF
A 2D drawing exchange format widely used for profiles and cut paths. DXF works well for flat parts and laser/waterjet cutting; for machined 3D parts we normally ask for STEP plus a PDF drawing.
DFM (Design for Manufacturability)
The practice of reviewing a design early to make it easier and cheaper to produce — adjusting radii, depths and tolerances before metal is cut. We offer a free DFM review with every enquiry; it is where most cost is saved.
Fixture
A device that holds a workpiece in position during machining. Good fixture design decides accuracy and throughput; complex parts may need custom fixtures, which is a normal part of quoting a job.
Workpiece
The raw material being machined into a part — a bar, plate or block. Specifying the workpiece material and starting size helps the shop plan stock, cutting strategy and cost.
Glossary
Materials, Surface Treatments & Compliance (18 terms)
Aluminum 6061-T6
The most widely used structural aluminium alloy — good strength, corrosion resistance, weldability and machinability. A reliable default for housings, plates, brackets and prototypes at a sensible cost.
Aluminum 7075-T6
A high-strength aerospace aluminium with fatigue resistance well above 6061. Chosen for highly loaded parts — impellers, motorsport components, structural brackets — where weight saving matters more than cost.
304 Stainless Steel
The standard general-purpose stainless — corrosion resistant, formable and weldable. Common for food, medical and washdown applications where hygiene and corrosion matter.
316 Stainless Steel
A stainless grade with added molybdenum for superior corrosion resistance, especially against chlorides and salt water. The choice for marine, chemical and coastal-environment components.
17-4 PH Stainless Steel
A precipitation-hardening stainless offering high strength and corrosion resistance after heat treatment. Used for valve parts, shafts and aerospace components where both strength and corrosion resistance are required.
Titanium Grade 5 (Ti-6Al-4V)
The workhorse titanium alloy — high strength, low weight, excellent corrosion resistance and biocompatibility. Demanding to machine; expect slower speeds, specialist tooling and higher cost than aluminium or steel.
Brass C360
A free-machining brass ideal for connectors, fittings, valve components and electrical parts. Machines beautifully, holds fine detail, and offers natural corrosion resistance.
PEEK
A high-performance engineering plastic with exceptional strength, chemical resistance and temperature stability. Machined as a metal substitute in medical, semiconductor and aerospace applications where standard plastics are not enough.
Delrin (POM)
An acetal plastic known for low friction, dimensional stability and easy machining. Common for jigs, fixtures, bushings and gears where metal would be over-specified.
Anodizing
An electrochemical process that grows a hard, corrosion-resistant oxide layer on aluminium. Type II gives coloured finishes; Type III (hard anodizing) gives a wear-resistant surface for functional parts.
Powder Coating
A dry paint process applied as powder and cured in an oven, producing a tough, uniform finish. Common on parts where appearance and durability matter more than tight tolerances on the coated surface.
Passivation
A chemical treatment that removes free iron from stainless steel surfaces and promotes a protective oxide layer. Standard practice for stainless parts going into food, medical and clean applications.
Bead Blasting
Blasting the surface with fine glass or ceramic beads to produce a uniform matte finish. Removes tool marks and improves appearance; often specified before anodizing for an even colour.
Deburring
Removing the sharp edges and burrs left by machining. Every part we ship is deburred — edges broken, threads cleaned, holes free of chips — so it is safe to handle and ready to assemble.
Material Certificate (MTC)
A document from the mill or supplier confirming the material grade, heat number and chemical composition. Required for aerospace, medical and other regulated industries; we keep certificates on file with every order.
ISO 9001
The international quality management standard. An ISO 9001 certified shop has documented processes for quoting, production, inspection and corrective action. We are certified and audited regularly.
RoHS
The EU directive restricting hazardous substances in electrical and electronic equipment. If your parts go into products sold in Europe, ask for RoHS-compliant materials — we can confirm compliance on request.
REACH
The EU regulation on chemicals, covering substances of very high concern in manufactured goods. For parts imported into Europe, buyers sometimes require REACH compliance declarations; we can provide them.
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