Why Drawings Get Sent Back
Design review rework is one of the most controllable sources of schedule loss in mechanical engineering. When drawings are returned with major comments — missing tolerances, ambiguous views, incomplete material specifications, inadequate weld callouts — the engineer faces not just the rework hours but the delay in downstream processes that were waiting on the approved drawing. Most design review failures are predictable and preventable.
This article identifies the most common reasons drawings fail design review and provides the preparation discipline that results in drawings being approved at first review or with only minor comments.
The Design Review Reviewer’s Perspective
Understanding what reviewers are looking for helps you prepare drawings that address their concerns proactively. Design reviewers are typically checking three things: completeness (is all the information needed to manufacture and inspect the part present?), correctness (is the information technically accurate?), and clarity (is the drawing unambiguous?).
Completeness failures are the most common. Reviewers regularly encounter drawings missing material specifications, surface finish callouts on functional surfaces, tolerances on critical dimensions, or detail views of complex features. These are not subtle errors — they are information that anyone manufacturing the part will need and will have to ask for if it is not on the drawing.
Pre-Review Checklist: What to Verify Before Submission
Title Block and General Information
- Part number and revision are correct and match the drawing file name.
- Material specification is complete: not just "steel" but the full designation (e.g., AISI 1045, ASTM A36, 6061-T6 aluminum).
- Surface finish — default finish specified in the title block note. Critical surfaces with different requirements called out explicitly.
- Drawing scale is specified and correct for the printed format.
- Weight is filled in (from CAD model mass properties) if the title block has a weight field.
Views and Sections
- The part can be fully manufactured from the views shown. If a feature is not visible in any view, it cannot be machined to the correct specification.
- Section views through complex internal features. A single exterior view of a part with internal bores, pockets, or passages is not manufacturable without sections.
- Section view arrows are correctly labeled and the section view is placed in the correct reading direction.
- Detail views are included for any feature where the main view scale does not allow legible dimensioning.
Dimensions and Tolerances
This is where most drawing rework originates. Before submission, verify:
- All features are dimensioned. Completely dimension every feature — do not rely on "the manufacturer will figure it out."
- Tolerances are specified on all functional dimensions. Title block tolerances apply to non-critical dimensions. Any dimension that affects fit, function, assembly, or interface must have an explicit tolerance tighter than title block default if required.
- Tolerances are achievable by the manufacturing process. A ±0.01 mm tolerance on a feature machined by manual turning is not achievable without premium cost.
- GD&T features — if geometric tolerances are used, datums are identified and referenced correctly, and the tolerance framework is complete and consistent.
Material and Process Callouts
| Callout Type | Common Deficiency | Correct Practice |
|---|---|---|
| Material specification | "Carbon steel" — not specific enough for procurement or inspection | "ASTM A36 / SS400 structural steel" — full designation |
| Surface treatment | Treatment specified but application area not defined | Call out treatment with coverage area or "all over" statement |
| Heat treatment | Condition only ("hardened") without hardness range or case depth | "Induction harden to 55–60 HRC, case depth 1.0–1.5 mm" |
| Weld symbols | Weld size missing or weld type symbol incorrect | Complete AWS weld symbol: type, size, length, pitch if intermittent |
| Thread callout | Partial callout ("M8 bolt pattern") without class | "M8 × 1.25 — 6H" for internal threads |
Preparing for the Review Meeting
If your design review involves a meeting rather than asynchronous markup, preparation for the meeting is as important as drawing preparation. Know your design decisions and be ready to defend them technically.
Technical Backup Documentation
Bring to the review: the relevant stress or analysis calculations (even if they are not part of the drawing package), any vendor data sheets for critical commercial components, and a brief summary of any design alternatives that were considered and rejected with the technical rationale. Reviewers who know that alternatives were evaluated and that the chosen approach has technical justification are much less likely to raise late-stage design direction challenges.
Known Issues and Open Items
If you know there are open items on the drawing — an interface dimension waiting on supplier confirmation, a tolerance that needs manufacturing input — list them explicitly at the start of the review. Proactive disclosure of known open items is more credible than having reviewers discover them. It also focuses the review on genuine technical questions rather than administrative completeness issues.
FAQ
Q: Is it better to use a peer review before formal design review?
Yes — strongly recommended. A peer review by a colleague who was not involved in the design catches completeness and clarity errors quickly, because the reviewer does not have the author’s context and cannot fill in missing information from memory. The peer reviewer’s experience of not being able to answer "how would I machine this feature?" from the drawing alone is the most reliable indicator that the drawing is incomplete. Most drawing reviews that fail at formal review would not have been submitted if a peer had reviewed them first.
Q: How detailed should drawing notes be?
Notes should contain information that cannot be expressed in dimension and tolerances or that applies to the drawing generally rather than to a specific feature. Material specifications, general surface finish requirements, inspection requirements, and manufacturing constraints belong in the notes. Notes should not repeat information that is already clear from dimensions and symbols. Excessive notes are hard to read and create confusion about which note applies to which feature.
Q: What is the most effective way to handle reviewer comments that you disagree with?
Respond to every comment with a clear disposition: accepted and resolved with a description of the change, or rejected with a technical rationale. "Will not change — the ±0.05 mm tolerance on this diameter is required to maintain the specified bearing fit; tightening is not necessary" is a legitimate disposition. Ignoring comments or making partial changes without explanation creates reviewer distrust and typically results in the comment being re-raised at the next review.
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