Two different tolerance decisions
As-cast geometry and CNC-finished features should be specified separately. A tight machining tolerance on a bore does not establish the same capability for every as-cast feature. Mark the features that will be machined and agree the casting allowance needed to produce them.
What a useful tolerance agreement contains
Identify the nominal dimension, feature type, datum reference, allowable variation and condition in which the part is inspected. Specify the applicable standard and edition when one is required. Resolve conflicts between general notes and individual dimensions before approving tooling.
Geometry and measurement matter
Review long dimensions, angular relationships, flatness, straightness and the relationship between separate features. These are not interchangeable with a simple linear tolerance. The drawing should make the functional requirement clear and the measurement approach practical.
Include the manufacturing sequence
Agree whether acceptance applies before or after heat treatment, machining and surface finishing. Coatings and later operations can affect the final interface. Review intermediate and final requirements together when they differ.
Approve representative parts
Define the sample inspection report and any repeat-production verification required. An approved sample should have a clear relationship to the production drawing, material condition and agreed process. Document changes rather than relying only on verbal approval.
Request a component-specific capability statement
Send the drawing and identify the dimensions that determine function. Ask for written confirmation of attainable requirements, any proposed drawing changes, inspection methods and quotation assumptions. Numerical limits should be supported by the relevant process and part evidence.
A downloadable white paper with company-specific tolerance data can be prepared after those data have been approved by engineering.
A tolerance handover, not a universal tolerance promise
| Review area | What to define in the enquiry |
|---|---|
| As-cast dimension | Nominal dimension, feature, agreed variation and inspection condition. |
| Machined feature | Final dimension, datum, finish and machining stock required. |
| Geometric control | Functional flatness, alignment or other drawing-defined requirement. |
| Approval evidence | Representative sample inspection and approved drawing revision. |