Specify Turned Parts from the Functional Features
Precision CNC turned parts are typically defined by rotational features and their relationship to mating components. A useful drawing shows the diameters, lengths, shoulders, bores, threads, grooves, and faces that control fit, alignment, or sealing. Do not rely on a general âmicron-levelâ claim to define part acceptance.
Show Datums and Critical Dimensions
Identify the datum axis and the relationships between diameters, bores, faces, and threads. Mark which features are critical and state the applicable tolerances on the controlled drawing. Add a supporting CAD model when it clarifies the geometry, while keeping acceptance dimensions in the drawing.
- Specify the material, finish, quantity, and drawing revision.
- Identify threads, grooves, shoulders, bores, and end faces.
- Mark functional alignment or concentric relationships.
- List critical dimensions and any measurement records required.
- Ask the supplier to note setup, finishing, and inspection assumptions.
For broader process and RFQ questions, see the CNC turning service guide. For how to identify mating interfaces, review precision machined components.
Confirm Inspection and Quote Scope
Ask which diameters, lengths, threads, and faces will be measured and what records are included. Confirm material, finish, quantity, secondary operations, packaging, shipping, and exclusions in the quotation. If the drawing has a conflict, resolve it before approving the quote.
Frequently Asked Questions
What features should a turned-parts drawing show?
Show diameters, lengths, datum axis, shoulders, bores, threads, grooves, faces, material, finish, and acceptance requirements.
How should I specify concentric or aligned features?
Define the datum axis and applicable geometric relationship on the drawing, then identify the features requiring verification.
Is a 3D model enough for a turned-parts quote?
Use the controlled drawing for dimensions, datums, tolerances, material, finish, and acceptance notes. The model can clarify geometry.
What inspection records should I request?
List critical diameters, lengths, threads, or faces and state the sample or lot reporting basis.
How do I compare turned-parts quotes?
Compare the same revision, material, finish, quantity, included operations, inspection, packaging, shipping, and exclusions.