CNC stands for computer numerical control. In CNC machining, a programmed machine guides cutting tools to remove material and produce a part from a block, bar or other workpiece.[1]
This is a subtractive process: the starting material is cut away. It differs from 3D printing, which builds a shape by adding material. A housing may start as a solid block; a shaft may start as round bar.[2]
The program controls movement, but the drawing, cutting tools, workholding and inspection plan still need to suit the part. For a buyer, the starting point is the required component—not a machine model or a promised number of decimal places.[3]
Explore CNC machining servicesA rotating cutter moves relative to a held workpiece. Milling is used for features such as flat faces, slots, pockets and hole patterns. A part may need more than one setup to reach its other sides.[4]
CNC milling servicesThe workpiece rotates while a cutting tool feeds along or across it. Shafts, sleeves, bushings and round shoulders are common examples. Flats or off-center holes may need live tooling or another operation.[5]
CNC turning servicesThree-axis machining uses linear X, Y and Z movements. In 3+2 machining, rotary axes position the part before cutting. Simultaneous five-axis machining can change the tool-to-part angle during a cut.[6]
5-axis machining servicesConfirm the part number, revision, material and quantities. Resolve conflicting dimensions or notes before treating the design as released.
CAD describes the geometry. CAM helps plan tool movements; post-processing converts that plan into code for the intended machine and controller.[7]
Choose a suitable blank, hold it securely and establish the workpiece location. Tool access and clamping need to be planned together.
Roughing removes most of the unwanted material. Finishing passes bring surfaces toward the specified size and surface condition. More setups may be needed.[4]
Deburring, coatings, heat treatment or other work belong in the agreed route when required. Identify which dimensions apply after the final process.
Check the agreed characteristics against the correct revision. Keep each delivery linked to its part identity, quantity and required records.
Share a suitable CAD file, such as STEP, when available. A model without manufacturing annotations may leave tolerances, finish and inspection requirements undefined.
Use the 2D drawing or agreed model-based definition to communicate critical features, units, material and notes. Do not assume a plain model contains every requirement.
A millimeter drawing and an inch drawing cannot be treated as interchangeable. Use the same revision in the model, drawing and purchase order.
An overall dimension tells you the size. Its permitted variation may be stated next to it or in an applicable general note.
Diameter, depth and through/blind condition are different requirements. A threaded hole also needs its thread specification and required depth.
Check internal radii, edge requirements and surface notes. Look for any datum references and geometric controls elsewhere on the drawing, using its specified standard.[8]
Teaching example only. It checks the arithmetic range, not a real part’s acceptance. Other drawing requirements, measurement uncertainty and the agreed decision rule are not evaluated.
In the example, 20.00 mm is the nominal value. Applying ±0.05 mm gives a lower size limit of 19.95 mm and an upper limit of 20.05 mm. The total interval is 0.10 mm, not 0.05 mm.
Position, orientation and form can require separate controls. A hole’s diameter can be within its size limits while its location is unsuitable for the assembly. Read the full drawing, including its geometric tolerances.[8]
A polished appearance is not proof of dimensional accuracy. Ask for the relevant surface texture requirement and the complete treatment specification, then identify which features must be checked after finishing.
| What to identify | What to include in the RFQ |
|---|---|
| Metal or engineering plastic | Name the material family, then the specific grade and condition. “Aluminum” or “plastic” alone may not identify what you need. |
| Material condition | Include the required temper, hardness or other specified condition. Separate the state of the purchased stock from the condition required at delivery. |
| Mating parts and working conditions | Describe the assembly, load, temperature, chemicals and contact surfaces that matter. The responsible design team should approve any material substitution. |
| Required treatment | Identify the surfaces to be coated, masked, polished or left as machined. Include the finish specification rather than relying on a reference color alone. |
Workpiece inspection compares a part’s measured geometry or dimensions with its design requirements. Checks can occur during machining as well as after it. Ask which features will be measured, by which method and in what condition.[9]
For your RFQ, separate material certificates, dimensional results and finishing records. List the records that must accompany the parts and identify the drawing revision they should reference.
Clarify whether a sample is for a fit check, a dimensional review or customer approval before a production release. Record unresolved items rather than treating a good-looking sample as approval of every requirement.
Send the same files, revision, material and finished condition to each supplier. A price based on an older model is not directly comparable with a quote for the current one.
List prototype, trial-batch and released production quantities separately. Ask what is included for setup, tooling, finishing, inspection and packing rather than comparing only the displayed unit price.
State when parts are needed and what has to happen before production or dispatch. Ask whether quoted timing includes external processing and inspection, and identify any approvals still outstanding.
No matching term. Try a shorter word or clear the search.
Plain-language definitions for orientation. Drawing terminology follows the standard specified on the drawing; see the technical references.[7][8][9]
No. Machining removes material from a starting workpiece; 3D printing adds material to build a shape. Both can be used during product development, but their design constraints and resulting parts are not interchangeable.[2]
You can start with the part definition and what it needs to do. Share any mandatory process restrictions, then ask the supplier to propose the route. The number of machine axes alone does not specify an achievable tolerance.
Provide a drawing when the model does not contain the complete manufacturing requirements. A properly agreed model-based definition can carry additional information, but a plain shape file should not be assumed to do so. Keep all supplied files at the same revision.
Start with the functional requirements set by the designer. Identify critical interfaces, apply the stated general tolerances where appropriate and agree the inspection scope. This guide does not prescribe a default tolerance for your part.
Yes. A round part can also have flats, slots or off-center features. These can require live-tool operations or a separate machining setup, depending on the equipment and geometry.[4][5]
Share the part number, current model and drawing, material and finished condition, quantity, critical requirements, requested records and delivery needs. A preliminary inquiry is still useful when something is unresolved—mark the open questions clearly.
Identify the missing information before releasing production. A supplier can ask questions or propose alternatives, but the authorized design or purchasing contact should confirm changes to material, dimensions, finish and acceptance requirements.
This guide provides an introduction, not a manufacturing specification or a substitute for the standard invoked by a drawing. The dimension example and drawing illustration are original teaching examples. Supplier-specific capability, inspection and acceptance must be agreed for the actual order. Technical references checked on 19 September 2026.