Prototype CNC Machining

Get metal and engineering-plastic prototypes machined from specified stock for assembly checks, functional tests and design iterations. Great Machining supplies housings, brackets, fixtures, shafts and sleeves with the finishes and dimensional records your project needs.

In-house CNC machining and dimensional inspection, with specialist finishing coordinated through selected partners.

  • One-piece projects considered
  • Controlled drawing revisions
  • Agreed dimensional records
Representative metal and engineering plastic CNC prototype parts

Prototype Parts for Your Next Build

Representative machined housing and matching cover for a prototype fit check

Housings and Covers

Machined pockets, locating bores and mounting faces for instrument mechanisms and equipment assemblies. Use the sample to check internal clearances, the mating cover and the interfaces that locate other components.

Representative CNC prototype bracket and positioning fixture

Brackets and Fixtures

Mounting brackets, positioning blocks and fixture plates with defined reference faces and hole locations. Identify the interfaces that matter to installation or repeat positioning so they can be machined and checked against the drawing.

Representative turned sleeve and stepped shaft prototype components

Shafts, Sleeves and Adapters

Turned components for mating diameters, shoulders, threads and mechanical connections. Define the fit, burr limits and relevant surface finish before using the sample in an assembly.

Images on this page are representative part, machining and inspection illustrations.

What Must the Prototype Establish?

Choose the sample around the decision you need to make next. A fit check, a material-dependent functional test and a revised design can need different specifications.

Next decision What the sample needs What to define
Assembly fit The mating geometry and relevant interfaces Reference faces, hole locations, clearances and the condition in which the assembly is checked.
Functional behaviour The specified stock grade, condition and relevant final finish Operating conditions, critical features and the test method and acceptance criteria.
Design iteration A controlled revision that incorporates the agreed changes Changed features, unchanged requirements and what the next sample will be used to check.

What the sample needs: The mating geometry and relevant interfaces

What to define: Reference faces, hole locations, clearances and the condition in which the assembly is checked.

What the sample needs: The specified stock grade, condition and relevant final finish

What to define: Operating conditions, critical features and the test method and acceptance criteria.

What the sample needs: A controlled revision that incorporates the agreed changes

What to define: Changed features, unchanged requirements and what the next sample will be used to check.

CNC prototyping is useful when machined interfaces or a specified stock material matter to the test. Printing can suit an early appearance model or geometry that cutting tools cannot reach. For functional testing, compare the actual material and manufacturing route, rather than treating similar-looking samples as equivalent.

CNC Routes for Different Prototype Geometries

Illustrative milling setup for a pocketed CNC prototype

Milled Housings, Plates and Brackets

CNC milling creates pockets, slots, mounting faces and hole patterns in plate, bar or block stock. Tool access, internal corner radii, pocket depth and the surfaces available for clamping affect the route. We review these features before confirming manufacture or any proposed design change.

Explore CNC milling services for more on prismatic parts.

Turned Shafts, Sleeves and Adapters

CNC turning suits rotational features such as bores, diameters, shoulders and threads. Slender sections need suitable support; side holes, flats and slots may require mill-turn work or another setup. The drawing defines which diameters and faces must relate to one another.

Explore CNC turning services for round components.

Illustrative CNC turning setup for a short sleeve prototype
Illustrative five-axis setup for angled mounting features

Features Across Several Faces

For angled holes, multiple mounting directions or complex reference relationships, we assess the appropriate multi-face or five-axis route. The choice depends on the part and its datums. Selected ground features, EDM work or other secondary operations are assessed separately, with their inspection requirements included in the quotation.

Materials That Match the Test

Specify the grade and condition used for your test. We machine the agreed material; an alternative grade or product form requires approval.

Representative plate bar and engineering plastic stock for CNC prototypes
Material option Typical prototype parts Details to keep with the drawing
6061-T6 aluminium plate or bar Housings, brackets and machined adapters Material standard, stock form, final fit and any anodized appearance requirements.
6082-T6 aluminium plate or bar Installation plates, fixture blocks and mechanical supports Specified grade and form, functional-face flatness and measurement condition; approval before substitution for 6061-T6.
7075-T6 aluminium plate or bar Mechanical prototypes and structural brackets when specified Material state, intended loading, finish and inspection requirements for the actual design.
Specified stainless steel Shafts, sleeves, connectors and instrument components 303 is mainly a bar-stock option; 304 and 316L may use bar or plate. Confirm the actual grade, environment and passivation requirements; these grades are not automatically interchangeable.
POM-C or POM-H stock Locating pieces, slides, bushings and contact components Actual material identity and the agreed measurement state. Material stress, temperature and moisture can affect dimensions.

Typical prototype parts: Housings, brackets and machined adapters

Details to keep with the drawing: Material standard, stock form, final fit and any anodized appearance requirements.

Typical prototype parts: Installation plates, fixture blocks and mechanical supports

Details to keep with the drawing: Specified grade and form, functional-face flatness and measurement condition; approval before substitution for 6061-T6.

Typical prototype parts: Mechanical prototypes and structural brackets when specified

Details to keep with the drawing: Material state, intended loading, finish and inspection requirements for the actual design.

Typical prototype parts: Shafts, sleeves, connectors and instrument components

Details to keep with the drawing: 303 is mainly a bar-stock option; 304 and 316L may use bar or plate. Confirm the actual grade, environment and passivation requirements; these grades are not automatically interchangeable.

Typical prototype parts: Locating pieces, slides, bushings and contact components

Details to keep with the drawing: Actual material identity and the agreed measurement state. Material stress, temperature and moisture can affect dimensions.

Other engineering plastics and metals can be assessed against the project specification. Availability and material-document requirements are confirmed with the quotation; this list does not imply stock on hand.

For more detail on grades, stock form and finished interfaces, see aluminium CNC machining.

Finish the Interfaces You Need to Test

Confirm whether mating dimensions apply before or after finishing. The sample’s surface condition should suit the check you intend to carry out.

Illustrative machined and anodized aluminium prototype interfaces

As Machined and Deburred

Retain the machined surface where that condition suits the test. Identify sharp-edge limits and any functional roughness requirement; visible tool marks and a specified surface roughness are separate acceptance questions.

Finished Aluminium Interfaces

For anodized samples, identify cosmetic faces, locating bores, threads and conductive contact areas. Agree masking, the appearance sample where needed and final dimensional inspection. Coating thickness alone is not a universal calculation for the change in every dimension.

Protection, Hardware and Assembly

Specify suitable passivation or protective treatment for the chosen metal. Threaded inserts and simple mechanical assembly can be included with agreed hardware, installation and checking requirements. Specialist finishing is coordinated with selected partners.

Precision and Inspection Around Critical Features

Identify the features that determine whether the prototype fits or can be used for its intended test. The drawing, datums and measurement method govern acceptance.

Feature type Assessment range Conditions
Selected metal dimensions To ±0.01 mm after assessment Stable, accessible features generally no larger than 100 mm; material, geometry, datums and measurement method reviewed.
Selected plastic dimensions Typically ±0.10 mm Actual material, residual stress, moisture, temperature, support and measurement state affect the result. Tighter selected features require a separate assessment.

Assessment range: To ±0.01 mm after assessment

Conditions: Stable, accessible features generally no larger than 100 mm; material, geometry, datums and measurement method reviewed.

Assessment range: Typically ±0.10 mm

Conditions: Actual material, residual stress, moisture, temperature, support and measurement state affect the result. Tighter selected features require a separate assessment.

Unmarked dimensions need an agreed general tolerance before manufacture. Tighter ground features are a separate operation; the most demanding tolerance is not a promise for every dimension on the part.

We use suitable dimensional methods, including CMM measurement where the range, probe and method fit the requirement. Reporting can include:

  • Agreed critical-feature results linked to the part number and drawing revision.
  • Full-dimensional or individual-part reports as a separately quoted scope.
  • Formal first article inspection with the required feature numbering, values, tolerances, results and methods.
  • Available material documents, order-specific CoC and agreed special-process records.

Routine first-piece checks and a formal FAI package are different deliverables. Define the records your receiving team needs when requesting the quote. See quality and inspection for the wider quality process.

Illustrative dimensional inspection setup for a machined prototype bracket

20 Bracket Prototypes in 7075-T6

A robotic end-tool development project required 20 bracket prototypes in 7075-T6, each with a 160 × 100 × 65 mm envelope and mounting features on several faces.

Geometry illustration of a multi-face 7075 prototype bracket type

The Required Interfaces

Selected hole diameters carried ±0.02 mm tolerances. Hole position was specified at Ø0.05 mm relative to the defined A/B/C datums, keeping the mounting relationships explicit.

The Manufacturing Route

The customer-approved model incorporated changes in non-critical areas. A five-axis route produced the multi-direction features, with the brackets supplied in the machined condition.

The Delivered Samples

The 20-piece prototype batch was completed in 10 working days, including the agreed dimensional records. Those records addressed the specified part features; application testing is a separate project step.

Geometry illustration of this prototype type.

Prototype Lead Time and Quotation

The schedule depends on the sample’s geometry, quantity, material, finishing and inspection work.

Prototype order Typical manufacturing lead time Included conditions
Simple aluminium or POM parts 5–7 working days Available stock, 1–10 pieces, normal tolerances and deburring. Special finishes are additional.
Complex or multi-face prototypes 8–12 working days Typically 5–20 pieces; special material sourcing and heat treatment are scheduled separately.

Typical manufacturing lead time: 5–7 working days

Included conditions: Available stock, 1–10 pieces, normal tolerances and deburring. Special finishes are additional.

Typical manufacturing lead time: 8–12 working days

Included conditions: Typically 5–20 pieces; special material sourcing and heat treatment are scheduled separately.

The manufacturing clock starts once the technical and order requirements, necessary payment and material availability are confirmed. Common specialist finishing typically adds 3–5 working days; special processes are scheduled separately. Customer approvals or later revisions have their own schedule. Manufacturing lead time excludes transit and customs clearance.

A one-off part still needs programming, setup, fixturing and first-piece checks. Tool access, material removal, tight features, specialist finishes and reporting add work. Give the sample quantity and any alternative quantities together so each can be quoted against the same revision and requirements.

From Enquiry to Inspected Samples

1. Describe the Next Build

Share a useful part description and what the sample needs to establish. Add the current model or drawing, quantity and known requirements when available.

2. Confirm the Quotation

We clarify the manufacturing route, material, finish, price, inspection deliverables and schedule. Any proposed geometry or specification change needs approval before manufacture.

3. Machine and Finish

Parts follow the approved requirements through machining and the agreed finishing or hardware operations. First-piece and process checks address the planned features.

4. Inspect and Dispatch

Final checks, labels and documents follow the order’s agreed scope. Parts are identified by the applicable part number, revision, quantity and batch for shipment.

Your Next Revision or First Batch

When the Design Changes

Identify the trial finding and affected feature, then send the current model and drawing with the new revision. Distinguish changed geometry, material, finish or inspection requirements from those that remain the same. If the model and drawing disagree, we clarify the controlled requirements before the next sample is made.

When the Sample Is Approved

Keep the approved drawing revision with the inspection requirements. Confirm the next quantity, material and finish, required records, packing and delivery plan. A different quantity can justify a different manufacturing route, which is reviewed before production.

Illustrative geometry revision of a machined fixture plate

Representative geometry-change illustration.

CNC Prototype Questions

Yes, one-piece CNC projects are assessed. Special material purchases, fixtures and setup can affect the economics, so the quotation confirms the scope for your part rather than applying a blanket minimum to every project.

Yes. A useful part description is enough to begin the enquiry. Share any model, sketch, sample information and known interfaces you have; the manufacturing requirements and controlled revision must be agreed before production.

It can help with the agreed geometry or interface check. A part cut from stock does not automatically establish the behaviour of a different cast, moulded or printed material and process. Identify which result the sample must support before choosing the route.

Functional or laboratory testing can be assessed as a separate scope with a defined sample, conditions, method and acceptance criteria. A dimensional report records the agreed measured features; it does not replace the equipment team’s application validation.

Use the website enquiry form for non-confidential information. For an NDA or restricted files, agree the confidentiality and file-transfer arrangement with us before sharing the drawings.

Start Your CNC Prototype Project

Your name, work email and a useful part description are enough to start. If known, include the sample quantity and what the next build needs to test.

Helpful details for quotation:

  • Current CAD model and controlled drawing revision, with the changed features identified for a revision.
  • Material grade, condition and stock form, or the operating requirements if material is undecided.
  • Critical dimensions, datums, finish, masking, hardware and inspection-document needs.
  • Quantity options, delivery country and the target dispatch or arrival date.

Upload non-confidential PDF drawings directly, or place CAD files such as STEP in a ZIP archive, up to 5 MB per file. Your quotation sets out the manufacturing route, agreed deliverables, price and confirmed manufacturing schedule.

Discuss an NDA and file transfer before sharing restricted drawings.