Specify CNC parts and compare quotes
CNC machining uses computer-controlled machines to work on parts. A quote primarily depends on the finished component: shape, material, quantity and functional requirements. A replacement made from a sample, a milled housing and a machined wood panel need different production planning. Describe what you need; the supplier clarifies the suitable process and missing technical information.
Turning, milling or combined machining?
Turning typically works on a rotating part, such as a shaft or round component. Milling produces surfaces, pockets, grooves and complex contours. Many parts need several operations. Do not choose solely by axis count or a machine name. Tool access, workholding and geometry also matter. Wood and sheet materials need different suppliers and tooling from precision metal parts.
Prepare a drawing, CAD model or sample
A 3D model describes geometry; a drawing can specify threads, critical dimensions, surfaces and inspections. Keep both at the same revision and state units. Without CAD, a sample or sketch can support the initial discussion. Measuring a sample and creating manufacturing data are additional work. For a worn replacement part, establish which dimensions reflect the original design and which reflect wear.
Clarify material and starting stock
The exact grade affects machinability and suitability. Aluminium, steel, stainless steel, plastics and wood are not interchangeable. State a known grade or describe the use. When reworking an existing part, the supplier needs its condition and available machining allowance. Agree who supplies the stock; unsuitable blanks may increase cost or prevent production.
| Starting point | Useful information |
|---|---|
| New parts | Grade, finished sizes, quantity |
| Rework existing parts | Condition, current sizes and desired change |
| Replacement from a sample | Function, mating parts, known original dimensions |
| Several variants | Quantity, material and sizes per type |
Require precision where it matters
A mating surface or hole for another component may need tighter requirements than an outer cover. Mark function-critical features instead of imposing very tight tolerances on every dimension. Extra grinding, EDM or inspection may add time and cost. Conversely, excessive variation at a fit may prevent the part from working. Agreed tolerances and inspection must suit the part; no identical accuracy guarantee applies to every supplier and material.
Price one-off parts and production runs properly
Programming, setup and workholding create work before the first part is finished. Preparation is spread over more units in an unchanged run. Quantity alone does not explain price: material removal, tool access, several machined faces, deep pockets, thin walls and finishing can matter. Do not compare different variants through an average price. Without a concrete specification, a generic CNC unit price is not informative.
What the quote should make clear
Check whether material supply, deburring, finish and agreed records are included. A low unfinished-part price may leave extra work outside the scope. For runs, clarify sample approval and subsequent changes. Delivery date, transport and VAT belong in the total. Binding technical requirements are agreed before production; the general word precision is not a substitute.
| Comparison point | Matching basis |
|---|---|
| Part and quantity | Same revision, quantity per variant and grade |
| Preparation | Account for programming, stock and workholding |
| Quality | Critical dimensions, finish and inspections actually ordered |
| Delivery | Sample, run approval, timing, transport and VAT |
Start well with a few useful details
State use, approximate size, quantity and available documents. Add known materials and important requirements. For different parts, describe quantity and specification per type in the common field. An initial enquiry does not require a machining strategy or tolerance standard. Drawings and confidential production data can be discussed later with the chosen firm.
Frequently asked questions
Can I request a replacement from a sample?
Yes. State function and condition. The firm assesses measurement of the sample and whether wear or missing information complicates reconstruction.
Do I need a finished CAD file?
Not for the initial enquiry. Describe the part and available documents. Suitable production data are prepared or agreed later; this work may cost extra.
Can CNC also machine wood or plastics?
Yes, with appropriately equipped suppliers. State the material; not every metal shop also works with wood or every plastic.
Why state critical dimensions?
They determine whether the part works in its application. Accuracy and inspection requirements affect production and should be reflected in the quote.
Are larger quantities always cheaper?
Preparation costs may be spread over more parts. Price also depends on material, geometry, variants and scope; compare complete quotes.
Are inspection reports and surface treatments included?
Only if agreed. State necessary records and finish requirements early and check whether they are included in the price.
