Almost every engineering drawing carries dimensions without an individual tolerance — and they are still not “tolerance-free”. What applies to them is the general tolerance from the title block, usually to ISO 2768. In the inspection plan these are exactly the dimensions that get handled badly: sometimes forgotten, sometimes carried without a tolerance. Both come back to bite you at the first article inspection at the latest.
What ISO 2768 covers
ISO 2768 defines general tolerances for dimensions without an individual tolerance. Part 1 covers linear and angular dimensions in four classes (f = fine, m = medium, c = coarse, v = very coarse), Part 2 covers form and position in classes H, K and L. So an entry such as “ISO 2768-mK” in the title block means: linear dimensions to class m, form and position to class K. The permissible deviation depends on the nominal size range — a 20 mm dimension in class m may vary by ±0.2 mm, a 200 mm dimension already by ±0.5 mm.
Why these dimensions belong in the inspection plan
A dimension without an individual tolerance is still a characteristic: it describes the geometry of the part, and the customer may expect it to lie within the general tolerance. Leave such dimensions out when ballooning and you deliver an incomplete first article inspection report — write them into the characteristic list without a tolerance and nobody can decide “pass” or “fail” when measuring. The clean approach: every one of these dimensions gets its numbered balloon, and the characteristic list carries the limit deviation derived from the class and the nominal size range.
Three traps from daily practice
- The title block gets overlooked. Without the class (mK, for example) no limit deviation can be derived. If it is missing from the drawing, that is worth a question to the customer — not an assumption.
- Reference dimensions get inspected. Dimensions in brackets, such as “(12.5)”, are auxiliary or information dimensions and normally not subject to inspection. They belong in the inspection plan only where that has been expressly agreed.
- Angles and chamfers slip through. 45° chamfers and angular callouts without a tolerance are also covered by the general tolerance — and they are the ones most often missed when ballooning.
How the software helps
During automatic detection, DrawingStamp Pro also balloons the dimensions without an individual tolerance and lists them in the exported characteristic list — so they do not drop out of the inspection plan merely because no tolerance is printed beside them. Dimensions in brackets are skipped by default and can be included deliberately if your customer requires it. Assigning the correct tolerance class from the title block remains a conscious look by the inspector — precisely the look that turns a list into a dependable inspection plan.
How a ballooned drawing becomes a complete first article inspection report is covered on the page FAI report software.