Drawing review checklist: 25 errors that cause scrap on the shop floor

Shops rarely scrap parts because a machinist made a mistake on a clear drawing. They scrap parts because the drawing was ambiguous and someone guessed. Here are the 25 checks we run on every drawing before release, grouped by where the problem usually hides.

Dimensions (1–7)

1. Every feature fully defined. Size, location and orientation of every feature can be found on the drawing.
2. No double dimensioning. Each value appears once; a duplicate eventually disagrees with the original.
3. No uncontrolled chain dimensions. Chains stack tolerances; dimension from a datum where the end position matters.
4. No dimensions to hidden lines when a section view would make them clear.
5. Reference dimensions marked as reference (in parentheses) and not used for inspection.
6. Units stated, and dual dimensions consistent if used.
7. Scale not used for manufacturing. “Do not scale drawing” note present; nothing depends on measuring the print.

Datums and tolerances (8–14)

8. Datums are real, accessible features the part can be fixtured on.
9. Datum order reflects how the part is located in assembly.
10. Tolerances come from function, not from a copied default block.
11. Every tolerance can be measured with equipment the shop or inspector has.
12. Fits use standard tolerance classes (ISO 286 or ANSI) where parts mate.
13. Geometric tolerances reference datums when required, and modifiers are intentional.
14. The general tolerance note matches the standard and the process (machined vs. fabricated).

Material, finish and process (15–19)

15. Material with grade and standard (for example “AISI 304” or “EN 1.4301”), not just “stainless”.
16. Surface finish where it matters functionally, and a general finish note.
17. Heat treatment with hardness and where it applies.
18. Coating or plating with specification and thickness, and masking where needed.
19. Edge condition: break sharp edges, chamfer size, deburr requirement.

Views and notes (20–23)

20. Projection symbol present and correct.
21. Enough views and sections to read every feature without guessing.
22. Notes do not contradict the model or other notes.
23. Threads fully specified: standard, size, pitch, class, depth.

Revision and release (24–25)

24. Revision in the title block matches the model, and the revision table says what changed.
25. Title block complete: part number, name, material, drawn and checked by, date, standard.

How to use the checklist

Print it or put it in your PDM workflow, and require the checker to mark every line, not just sign the title block. When a supplier raises a question that the checklist would have caught, the checklist worked; when it would not have, add a line.

The five errors we see most often

Across the drawings we review, a handful of problems come back again and again. They are worth checking first:

1. Tolerances copied from a template, tighter than the function needs. They do not cause scrap directly; they cause expensive quotes and suppliers who ignore tolerances because “they are always too tight”, which then causes scrap on the features that do matter.
2. Datums that cannot be fixtured: a datum on a cast surface that will be machined away, or on a small face the part cannot rest on.
3. Missing finish or coating, discovered after the parts are made.
4. Stale revisions: the PDF says revision B, the model is at revision C, and the supplier received the PDF.
5. Threads specified by size only (“M8”) with no depth, class or, for blind holes, drill depth.

How to check tolerances quickly

For each toleranced dimension, ask two questions: what happens in assembly if the dimension is at the limit, and how will it be measured? If nothing bad happens at the limit, the tolerance may be too tight. If nobody knows how to measure it, it will either be skipped or argued about. A dimension that passes both questions is fine.

Checking against the model

Most drawings today come from a model, which means many errors are differences between the two: a dimension overridden on the drawing, a feature changed in the model after the drawing was detailed, a hole callout typed instead of linked. Before release, rebuild the drawing, look for dimensions shown in a different colour (overridden or dangling), and compare the revision of the model file with the title block.

Who should sign

The checker’s name in the title block should mean something. Agree what “checked” means in your company: the full checklist applied, not a glance. If an outside reviewer checks drawings for you, ask for the marked-up PDF with each item, so the review is visible and auditable.

Turning returns into lessons

Every supplier question, nonconformance report or scrapped batch caused by a drawing is free information. Log the cause in one line, map it to a checklist item, and add a new item when none fits. After a year, the checklist reflects your parts and your suppliers instead of a generic list, and the most common errors stop appearing.

A checklist for purchased-part callouts

Drawings of assemblies also fail on the parts you do not make. Check that every purchased item on the drawing or BOM has a manufacturer and part number (not just “M8 bolt” or “bearing”), that alternates are listed when you accept them, and that critical properties are stated where substitutes are common: bolt property class, bearing clearance class, seal material. A supplier who substitutes a “same size” part is following the drawing if the drawing did not say more.

Common objections

“We don’t have time to check every drawing.” A rejected batch costs more than the check. Start with parts that go to new suppliers or have tight tolerances.

“Our machinists know what we mean.” Until the part goes to a different shop, or the machinist retires.