Table of Contents
Why Designers Must Share Their Design Intent with CNC Machining Manufacturers
— In Tribute to Segi’s Contribution in Our Group
Opening Acknowledgement
In our DFM group, member Segi shared several valuable experiences. These stories highlight the complexity of real-world engineering and remind us of an often-overlooked truth: many product failures are not caused by designers “not knowing design,” nor by manufacturers “not knowing production,” but by a more subtle yet critical issue — the lack of design intent being communicated effectively.
In precision engineering and CNC machining projects, this gap becomes even more critical. Even when manufacturers use advanced 5-axis CNC machining centers, ISO 9001–certified processes, and the latest inspection tools, products can still fail if the design intent is not passed clearly from designers to the machining team.
It is thanks to engineers like Segi, who are willing to bring real-world cases into open discussion, that we can reflect as a community and continue exploring better ways to improve collaboration between design and manufacturing.
The Background Problem: Silos and Lack of Integration
Design, CNC machining, inspection, and materials are theoretically tied together through GD&T (Geometric Dimensioning and Tolerancing);
In practice, however, these areas are too often separated into silos;
There is no dedicated role ensuring integration across these functions.
The result: each function may appear “correct” on its own, yet when the results are combined, systemic problems emerge. In other words: Local correctness does not guarantee system correctness.
Case One: Parts in Spec, But System Failure
Segi described a typical scenario:
Every part appeared to meet its tolerance requirements, and assembly followed procedure;
Yet the final system test still failed.
Further investigation uncovered that:
There were issues in the GD&T coding of the drawings;
More importantly, the Datum feature selection was inappropriate, which distorted tolerance stack-up calculations.
This example shows how without accurate datum definitions and clear design intent, even “in-spec” CNC machined components can fail to function as a system. Of course, this is just one situation — there are many other ways such gaps can manifest, depending on the product and process.
Case Two: Cartridge Datum Reference Frame Conflict
Segi also shared another case related to a handheld printer cartridge:
The initial assumption was that the new cartridge would inherit the existing Datum Reference Frame (DRF), enabling existing tooling to be reused;
But due to space limitations, the design team redefined the DRF, choosing features that were relatively unimportant in the original design.
The consequences were clear:
Interface tolerance calculations failed;
Electrical connection tolerances were also incorrect;
The printer and cartridge became incompatible, forcing a last-minute adjustment by tightening tolerances on the cartridge side.
Segi’s conclusion was straightforward: if design intent is not communicated, even thorough downstream checks may not be able to catch such errors in time.
Again, this is just one illustration — and it highlights how design choices, when not fully shared, can cascade into system-level issues in CNC machining projects.
Engineering Analysis: Root Causes
Drawings describe results, not reasons. CNC manufacturers may execute what is written but cannot grasp the rationale behind the design decisions.
Local optimization ≠ system optimization. Issues that surface late in the process multiply costs exponentially.
Accountability gaps. Each department insists “my part is fine,” while systemic failures remain unresolved.
Practical Measures in CNC Machining Projects
Unified Reference File at the CNC Sample Stage
A dedicated engineer consolidates design requirements and intent into a single document;
This file becomes the standard reference for all subsequent CNC machining and inspection stages.
Cross-National / Cross-Functional Communication
In international CNC machining projects, detailed early communication between design teams and manufacturers is crucial to align intent, materials, and machining processes.
Documenting Design Rationale
Critical features and datum choices should include an explanation of why decisions were made;
This enables CNC machining engineers to understand the logic, not just the symbols.
Closed-Loop Process Control in CNC Manufacturing
Standardized workflows and layered responsibilities ensure that “fix it later” is eliminated from the CNC machining system.
Additional Insights from the CNC Manufacturer’s Side
Process feasibility: Some designs are theoretically possible but prohibitively expensive to machine. When intent is known, we can recommend more practical CNC machining strategies.
Material vs. machinability: Different materials may deliver the same performance but vary drastically in machining difficulty and cost.
Inspection priorities: When designers clarify which dimensions are critical to function, CNC inspection resources (CMM, gauge, etc.) can focus on what truly matters.
Only when CNC machining manufacturers understand the “why” can they act as true partners in product development, rather than passive executors.
Conclusion
Segi’s experiences remind us that the root cause of many failures lies not in poor design or poor manufacturing, but in the lack of design intent being communicated effectively.
Sharing design intent is not an extra burden. On the contrary, it is the most cost-effective insurance against rework, production delays, and catastrophic losses in CNC machining projects.
By building stronger bridges between design and manufacturing, we can ensure that products move from concept to reality more smoothly, more reliably, and with fewer painful surprises.
This is also why we created our professional group: a space where designers, engineers, and CNC machining manufacturers can openly exchange experiences and insights.
If you have ever faced similar challenges — or if you want to prevent them in your own CNC machining projects — we welcome you to join the conversation. Together, we can bridge the gap between design and production, and make product development simpler, smarter, and far more reliable.
