Drawing Discrepancies, Non-Conformance, and Document Control

Why Drawing Discrepancies Matter

Every part you machine starts with a drawing. If that drawing contains conflicting, ambiguous, or incomplete information, you may spend hours cutting metal only to produce a part that cannot be used. Worse, a bad part that slips into an assembly can cause equipment failure or injury. Catching drawing problems before you start—and documenting them correctly when you find them—is a professional responsibility, not an optional step.

Types of Drawing Errors

Conflicting tolerances occur when two callouts on the same feature disagree. For example, a title block might state a general tolerance of ±0.010 in. while a local callout on the same dimension reads ±0.005 in. Without knowing which controls, you cannot set up the job.

Missing datums create ambiguity in GD&T because every geometric tolerance must reference a datum structure unless it is specifically a form tolerance (such as flatness or cylindricity). A perpendicularity callout with no datum reference tells the machinist nothing about which surface to measure from.

Undefined surface finish means the drawing shows a surface finish symbol with no roughness value (Ra or RMS) filled in. You cannot verify the surface, and an inspector cannot accept or reject it.

Incorrect projection views happen when a third-angle or first-angle projection is mixed up, a view is mislabeled, or a detail view arrow points the wrong direction. Reading the wrong view can cause you to machine a mirror-image feature.

Obsolete revisions are drawings that have been superseded by a newer release. Using an old revision is one of the most common—and most costly—shop-floor errors.

Illegible notes may be caused by poor print quality, overprinting of text, or damage to the drawing file. Any note you cannot read completely must be treated as missing information and flagged before work begins.

Document Control Basics

Document control is the system that ensures only the correct, approved version of a drawing is used for production. Key concepts:

• Revision control: Each released drawing carries a revision identifier (typically a letter or number, such as Rev A, Rev B, or Rev 1, Rev 2). Every change to a released drawing requires a formal process and increments the revision level.
• Drawing release: A drawing is not authorized for production until it has been reviewed and signed off by engineering and quality. A drawing still in draft ("preliminary" or "not released") may not be used for manufacturing.
• Engineering Change Order (ECO): The formal document that authorizes a change to a drawing or specification. An ECO describes what changed, why, and which revision level results from the change.
• Current released revision: On the shop floor, only the current released revision may be used. If you receive a job packet and the drawing in it does not match the revision number shown in the document control system, stop and resolve the discrepancy before machining.
• Obsolescence: Older revisions must be removed from the work area and either archived or marked "VOID" or "SUPERSEDED" so they cannot accidentally be used.

In a simulated document control folder, you should be able to look at the revision block, compare it to the master index, and confirm you have the correct document.

Non-Conformance Reports (NCRs)

A non-conformance report (NCR) is the formal record that a part, material, or process does not meet the applicable requirement. Completing an NCR is not an admission of fault—it is a professional, quality-driven response to a real problem.

A standard NCR typically includes:

1. Part identification: Part number, description, revision level of the drawing used.

2. Description of discrepancy: Which dimension or callout is out of compliance, by how much, and how it was discovered.

3. Affected quantity: How many parts are nonconforming.

4. Root cause (if known): For example, machined to an obsolete drawing revision.

5. Recommended disposition: One of three standard choices:

• Use-as-is (UAI): Engineering determines the deviation does not affect form, fit, or function.
• Rework: The part can be brought into compliance by additional machining or other corrective operation.
• Scrap: The part cannot be corrected and must be discarded.

6. Signatures and dates: Originator, quality review, and (for UAI) engineering approval.

The disposition decision is made by qualified personnel—often a quality engineer or the engineering team—not unilaterally by the machinist. Your job is to document accurately and completely so that decision can be made with full information.

Safety Note

Drawing errors can create safety hazards beyond scrap parts. If a structural or pressure-boundary component is machined to the wrong tolerance, it may fail in service. Always stop work and flag the discrepancy rather than making an assumption and continuing. Never alter a drawing or note on your own authority. Use proper personal protective equipment (PPE) when handling any materials in the shop, and follow lockout/tagout procedures if the machine must be accessed during a hold.

Summary

Before cutting, verify you have the current released drawing revision. Read every callout and check for the six common error types. When you find a problem, document it using the NCR process with accurate part identification, a clear description, affected quantity, and a logical recommended disposition. These habits protect quality, protect you, and protect everyone who uses the finished part.