What tolerance is normal?

General machining is often quoted to around ±0.1 mm unless the drawing says otherwise, and tighter tolerances are possible where they are needed. Tighter tolerances cost more, so apply them only to the features that must fit.

Can I get one piece made?

Yes. Many workshops take prototype or single-piece jobs. The price per piece will be higher than in a batch, because the setup is spread over one part.

Should I send a 3D file or a drawing?

Both if you can. The drawing shows tolerances and finishes. The 3D model shows the exact shape. Together they avoid misunderstandings.

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CNC machining

Turned and milled parts, one-offs to production runs, in metals and plastics.

CNC machining removes material from a block or bar with computer-controlled machines to make an exact part. It suits prototypes, spares and production runs, and the same drawing can be quoted very differently depending on the workshop's machines and experience.

CNC turning makes round parts on a lathe: shafts, bushes, pins and threaded parts. CNC milling makes prismatic parts: plates, housings, brackets and fixtures. Machining centres with more axes can make complex shapes in one setup.

Workshops differ in machine size, number of axes, tolerance capability and inspection equipment. A workshop that suits a small precision part may not be right for a large housing.

Materials commonly used

Mild steel, alloy steel and stainless steel
Aluminium alloys
Brass, copper and bronze
Engineering plastics such as nylon, delrin (acetal) and PTFE

What to send with your requirement

A dimensioned drawing (PDF) with tolerances, and a 3D file (STEP) if available
Material and grade, and any material certificate you need
Quantity now and expected later
Surface finish, coating or heat treatment, and who arranges it
Inspection requirements, such as a first article report

What affects the cost

Material and the size of the raw stock
Machining time: features, depth of cuts, and number of setups
Tolerances: tighter tolerances need slower machining, better machines and more inspection
Quantity: setup cost is spread across the batch
Finishing, heat treatment and inspection

Common mistakes to avoid

Specifying tight tolerances everywhere when only a few features need them
Sending a drawing without the material grade
Not saying which finish or coating is needed
Asking for a quote on one piece and expecting production pricing

Need CNC machining done?

Post your requirement free. Workshops that take your kind of job see it and get in touch. You only talk to the ones that fit.

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Frequently asked questions

What tolerance is normal?: General machining is often quoted to around ±0.1 mm unless the drawing says otherwise, and tighter tolerances are possible where they are needed. Tighter tolerances cost more, so apply them only to the features that must fit.
Can I get one piece made?: Yes. Many workshops take prototype or single-piece jobs. The price per piece will be higher than in a batch, because the setup is spread over one part.
Should I send a 3D file or a drawing?: Both if you can. The drawing shows tolerances and finishes. The 3D model shows the exact shape. Together they avoid misunderstandings.

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