A casting tolerance grade is not a standalone millimeter capability. To use a tolerance table correctly, the buyer and supplier need the applicable standard edition, nominal dimension, dimension type, casting condition and any individual drawing requirements. Quoting a grade without those inputs leaves the acceptance basis incomplete.
Establish the Controlling Drawing Requirement
The public scope of ISO 8062-3:2023 concerns general dimensional and geometrical tolerances and machining allowances for castings using indicated dimensions. Obtain the controlled standard used by the contract and confirm that its scope fits the drawing. This guide does not reproduce the standard's numerical tables.
Record the full designation and edition. Identify whether a requirement comes from a general note, an individual dimension, a geometrical control or a customer specification. If documents disagree, resolve precedence through the buyer's engineering process before accepting the order.
Distinguish Total Width From Plus/Minus Notation
A total tolerance width and a bilateral plus/minus value are not the same number. If a requirement explicitly centers a tolerance zone about the nominal value, the plus/minus magnitude is half of that total width. Do not assume a centered zone where the controlling requirement defines a different disposition.
When transferring a value from a standard, check the nominal-size band, boundary inclusion, grade, units and zone disposition. Have a second reviewer reproduce the lookup. A copied table that mixes total widths and plus/minus values can change the acceptance requirement even when the heading looks correct.
Separate As-Cast and Machined Features
| Feature group | Drawing/RFQ decision | Evidence to agree |
|---|---|---|
| General as-cast dimensions | Applicable general tolerance requirement and exceptions | Layout or other agreed dimensional inspection |
| Core-formed passages and local walls | Location, minimum condition and inspection access | Section/measurement plan appropriate to the geometry |
| Machined bores, ports and datums | Individual dimensions and geometrical controls | Defined datum setup, gauges or CMM plan |
| Sealing or mating faces | Flatness, surface texture and final condition | Dimensional and functional evidence required by the design |
| Stock for machining | Required allowance and reference state | Allowance review before tooling release |
A casting grade does not automatically establish a finished bore's position, a sealing face's flatness or a functional clearance. State the necessary controls for those features individually.
RFQ CTA
Have a casting project? Submit the RFQ details, then email your drawing for a structured quote review.
Send the drawing, target alloy, finishing scope, MOQ, and delivery timing. Bohua will review it like a real sourcing project, not a generic contact request.
Compare Manufacturing Routes on Equal Terms
Do not compare process accuracy through unrelated generic plus/minus ranges. Use the same nominal dimension, feature, geometry, alloy, process condition and inspection method. Ask the supplier to identify the proposed capability evidence and any design changes needed to support it.
Tool construction, core location, local section, heat treatment and machining sequence can affect the result. Separate a proposed target from demonstrated capability and from the customer's acceptance limit. A target printed in a quotation is not a completed capability study.
Prepare the Inspection Plan With the RFQ
- •Mark the nominal dimension and controlled feature, not only the overall part size.
- •Name the standard edition and any individual exceptions.
- •Define datums, part support and the inspection state.
- •Distinguish casting allowances from finished dimensions.
- •Identify inaccessible surfaces and how they will be verified.
- •Agree sample quantity, required reports and disposition of nonconforming results.
FAQ
Can one general casting grade control every feature?
No. Review its scope and specify individual requirements for features that need different controls.
Can I copy a CT or DCTG number from a supplier brochure?
Only as a discussion starting point. Confirm the designation, edition, dimensions and applicability in the controlled drawing package.
Should every tight feature be machined?
That is a design and manufacturing decision. Compare the required function and acceptance with a verified route instead of inferring machining need from one general tolerance grade.
Send the marked drawing and inspection expectations through the tolerance RFQ route.
Project CTA
Ready to Source This Part?
Submit the RFQ details here, then email your drawing for a structured DFM review and quote.