Edition #14 - The Hidden Power of a Good Drawing

Have you ever been in a situation where a part arrives from a supplier that is not fit for purpose? Maybe the tolerances are off, the clearances do not work, or there are tooling marks on a critical face.

If your part drawings are clear, you can send the parts back as non-conforming. But if your drawings fail to communicate the critical aspects of your product, you may have no recourse.

Clear, unambiguous part and product drawings are an important tool for reducing product risk. They ensure everyone involved, from internal teams to external suppliers, has the same understanding of what is required.

Good drawings or specifications are also essential for diagnosing problems, both in production and once a product is in the market. They make it easier for suppliers to provide feedback, raise concerns, or suggest improvements early, before costly tooling or production errors occur. As your business grows, they help maintain consistency by reducing reliance on verbal instructions or institutional knowledge.

Your product drawings also form a key part of the contractual agreement between you and your supplier. They define whether the supplier has met their obligations if something goes wrong.

To reduce risk and protect both parties, every drawing should include a few essential elements:

1. Unique drawing or part number and revision: Ensures tooling and production are based on the correct and current design, avoiding errors from outdated references.
2. Exact specification of material and key properties: Prevents substitutions that compromise performance or compliance.
3. Part finish and coating thickness: Surface finish affects function, aesthetics, and corrosion resistance. Coating thickness impacts fit and durability.
4. Part colour: Helps avoid rework or scrap caused by incorrect colour batches and informs tooling or surface preparation decisions.
5. Product size dimensions as reference: Confirms the part has not been inadvertently scaled during file handling or translation.
6. All critical dimensions and tolerances: These affect performance, safety, and durability.
7. Interface dimensions, tolerances, and fit types (for example, interference, sliding): Ensure correct fit with mating parts.
8. Dimensions tied to regulatory compliance: Prevents non-compliance, liability, or recalls.
9. Dimensions to be checked on first-off or start-of-batch parts: Catches early issues before full production.
10. Reference to the 3D model file and revision: Links the drawing to the exact geometry used for tooling.
11. Identification of primary or critical faces: Ensures cosmetic or functional surfaces are protected and properly handled throughout manufacture.

Your drawings are also valuable intellectual assets and should be treated as such. In litigation or regulatory investigations, you may be required to submit them as part of your documentation.

The quality of your drawings says more than just what a part looks like. It signals:

• the level of design maturity within your business
• the thoroughness of your engineering processes
• your team’s approach to safety, compliance, and traceability
  

Poorly prepared or inconsistent drawings suggest product development may have been rushed, poorly controlled, or not fully understood.

In contrast, clear, complete, and professionally presented drawings reflect a business that takes its responsibilities seriously. They demonstrate a culture of rigour and accountability, qualities that carry weight with legal counsel, investigators, and insurers.

In high-stakes situations, your drawings are not just tools for manufacturing, they are evidence of how well you manage product risk.