What Happens When Tolerance Specifications Are Missing？
In the field of precision machining, it is common to receive engineering drawings that include only basic dimensions without clearly defining tolerances, machining methods, or critical geometric requirements. Although such drawings may appear “complete,” they often lead to misunderstandings, delays, and even unusable parts during manufacturing.
Why Clear Tolerance Markings Matter？
Even when a dimension appears correct, an undefined tolerance can result in completely different interpretations between the designer and the manufacturer.
For example, a 10 mm hole may require ±0.01 mm for proper functional fit. However, if a machine shop follows a general ±0.1 mm tolerance, the final part may fail in assembly, compromise performance, or require costly rework.
How We Handle Incomplete Engineering Drawings
When encountering drawings that lack essential information, we proactively confirm the following with customers：
- Functional dimensions：Identify which dimensions affect assembly or operation, and which are merely structural.
- Geometric tolerances and surface requirements：Clarify any needs for parallelism, perpendicularity, concentricity, or surface roughness.
- The part’s role in the system：Determine whether the part is critical or supportive to decide the appropriate precision level.
This upfront communication helps fill in missing details, reduces quality risks during mass production, and prevents unnecessary rework costs.
Practical Recommendations and Best Practices
- Specify key dimensions and explicit tolerances：All functional dimensions should have defined tolerance values.
- Refer to manufacturing standards：If tolerances are not provided, general tolerances may be assigned based on ISO or ASME standards.
- Communicate early：Discuss critical dimensions and process risks during the prototyping phase to prevent issues before they arise.
Engineering Mindset：Quality Begins with the Drawing
Manufacturing quality does not depend solely on machines or cutting tools—it begins with the engineering drawing. The clearer the drawing and the more aligned the understanding between both sides, the lower the process risks and the higher the efficiency and product quality.
Proactively clarifying every detail in the drawing is the foundation of a successful project.
