Skip to content 
Project at a Glance
- Component: 7075-T6 custom steering knuckles (Suspension system)
- Core Challenge: Machining a 2.50 mm thin-wall flange with asymmetrical geometry
- Process Route: 5-axis CNC milling + black anodizing
- Delivery Result: Completed and shipped to the Netherlands within 9 workdays
Automotive Prototype Project Background
In May 2026, our project manager, May, received a RFQ from Bailey Summer Hoogendoorn, representing the mechanical engineering team at the Rotterdam University of Applied Science. The team was developing a prototype vehicle for the Shell Eco-marathon and required the manufacturing of two custom aluminum steering knuckles for the front wheel suspension system.
The project timeline required the components to be machined, verified, and delivered to the Netherlands within a 9-workday window. Because this academic research project operated under a limited research budget, FastPreci chose to support the academic research initiative; following an internal discussion, we agreed to provide partial sponsorship. As a manufacturing engineer participating in the project, I cooperated with May to conduct the initial engineering review and establish a production routing to meet the dimensional requirements of the suspension assembly.
Technical Specifications Summary
| Parameter | Project Requirements |
| Component Name | Custom Steering Knuckles (Suspension System) |
| Primary Material | 7075-T6 Aluminum Alloy |
| Critical Assembly Tolerance | ±0.05 mm (Cylindrical shafts & press-fit bores) |
| Surface Roughness | Ra 3.2 |
| Surface Treatment | Anodized (Black, Glossy) |
| Primary Inspection Tool | Coordinate Measuring Machine (CMM) |
| Production Timeline | Within 9 Workdays (Delivered ahead of schedule) |
| Application Environment | Shell Eco-marathon Prototype Vehicle |
Asymmetrical Geometry & Thin-Wall Machining Risks
Upon evaluating the engineering blueprints, we identified two primary geometric constraints that introduced manufacturing risks:
Asymmetrical Workholding Complexity
The steering knuckles feature an asymmetrical geometry with compounding angles. Processing this on a standard 3-axis milling machine would require three to four independent fixturing setups. Each manual rotation and re-clamping operation introduces the risk of indexing errors. These cumulative errors would affect the ability to maintain the strict ±0.05 mm tolerance specified for the critical bearing bores and cylindrical shafts.
The 2.50 mm Thin-Wall Feature
The component design included a flange section with a wall thickness of 2.50 mm. Machining 7075-T6 aluminum down to this thickness introduces a risk of material deflection. The mechanical forces and localized thermal expansion generated by milling cutters can cause the thin wall to push away from the tool, resulting in wall-thickness variations, chatter marks, or geometric warping.
DFM Review and 5-Axis Process Routing
To address these constraints before cutting material, we initiated a direct Design for Manufacturability (DFM) review with Bailey’s team.
The Initial Manufacturing Proposal
To minimize the risk of thin-wall distortion and reduce fixture development time, I initially proposed a segmented manufacturing strategy. The plan was to machine individual, simpler sub-components on a standard mill and subsequently join them via precision welding.
Structural Constraints and Final Process Selection
May communicated these DFM notes to Bailey, who stated that the suspension knuckles would undergo variable dynamic loads during track testing. Introducing a weld joint would create a heat-affected zone (HAZ) where the mechanical properties of the 7075-T6 alloy would degrade, establishing a potential fatigue failure point. The application demanded a unibody, single-piece construction.
Based on these structural parameters, we routed the project to our 5-axis CNC machining center, executing a two-part manufacturing strategy:
- Single-Setup Fixturing: Securing the raw 7075-T6 block in a single clamping setup allowed multi-angle spindle access automatically. This eliminated manual re-indexing, mitigating cumulative setup errors and maintaining the concentricity of the ±0.05 mm bores.
- Thin-Wall Control Strategy: To machine the 2.50 mm flange without deflection, I programmed multi-pass pocketing routines with temporary structural supports, reducing the depth-of-cut and optimizing feed rates to minimize cutter pressure throughout the cycle.
CMM Inspection and Quality Control
Following the machining operations, the components were cleaned and routed to our inspection lab for verification against the technical specifications:
- Dimensional Inspection: We utilized a Coordinate Measuring Machine (CMM) to probe the critical cylindrical interfaces and mounting holes. The metrology data confirmed that all critical assembly dimensions fell within the required ±0.05 mm tolerance envelope.
- Surface Topography and Coating: The raw machined surface was controlled to an Ra 3.2 roughness baseline. This uniform surface finish allowed for consistent chemical bonding during the subsequent Black Glossy Anodizing phase. The surface treatment provided the necessary corrosion resistance while maintaining the final precision tolerances of the assembly positions.
Production Timeline and Logistics Management
While I managed the shop-floor execution, May supervised the project timeline and logistics tracking. May provided regular updates, including active Work-in-Progress (WIP) photos of the custom steering knuckles during the milling cycle.
Additionally, May coordinated the international logistics documentation, customs paperwork, and import duty specifications for the Netherlands upfront. This preparation ensured that the components bypassed potential customs bottlenecks. The production run was completed and delivered ahead of the committed 9-workday schedule.
Client Feedback and Testimonial
Following installation and assembly, Bailey Summer Hoogendoorn provided the following review via Trustpilot:
“From the very beginning, they actively thought along with us about what was technically possible and how the parts could best be manufactured. Their engineering input and willingness to help optimize the design were incredibly valuable for our project.”
“During manufacturing, they even sent photos of the parts in progress, which gave us a lot of confidence and was genuinely great to see. They also kept me fully informed regarding shipping, customs, and import costs, which made the entire process smooth and stress-free. The final quality of the aluminum parts was exactly what we hoped for.”
Manufacturing Insights for Sourcing Teams
This prototype project demonstrates several manufacturing realities for complex suspension components:
- Pre-Production DFM Collaboration: Proactive engineering reviews are necessary to balance structural requirements with machining realities. Identifying risks like thin-wall deflection or tolerance stacking before production prevents material waste and schedule delays.
- Multi-Axis Equipment Utilization: Asymmetrical components with tight concentricity requirements benefit from 5-axis CNC machining. Reducing the number of independent workholding setups is an effective method to eliminate cumulative fixturing errors.
- Direct Engineering Communication: Eliminating communication layers between the client’s design team and the factory’s production engineers ensures that technical requirements are accurately translated to the shop floor.
Need 5-Axis Machining for Thin-Wall or Tight-Tolerance Aluminum Components? Skip the sales filters and get feedback straight from the shop floor. Upload your 3D STEP/STP models, 2D tolerance drawings, material specifications, order quantity, and target delivery date. Our manufacturing engineers will conduct a direct DFM review to identify production risks and provide an optimized routing strategy.
FAQs
Why is 5-axis CNC machining required for asymmetrical automotive steering knuckles?
Asymmetrical geometries with compounding angles require multiple fixturing setups on standard 3-axis mills, risking cumulative indexing errors. FastPreci uses 5-axis CNC machining to secure the raw 7075-T6 block in a single clamping setup. The spindle accesses all features from multiple angles automatically, eliminating manual re-indexing and maintaining feature concentricity.
How did FastPreci control ±0.05 mm tolerance on critical assembly bores?
To achieve ±0.05 mm tolerance on bearing bores and shafts, FastPreci executed all critical roughing and finishing operations within a single 5-axis setup. Eliminating part re-clamping between operations removed manual positioning deviation. The final alignment and geometric relationships were governed entirely by the mechanical positioning accuracy of the CNC machine.
How was thin-wall deflection managed when milling 7075-T6 aluminum down to 2.50 mm?
To prevent material deflection and thermal expansion when milling down to 2.50 mm, FastPreci programmed multi-pass pocketing routines and added in-process structural supports. Machining risks like chatter and geometric warping were minimized by reducing the depth-of-cut and optimizing feed rates throughout the cycle to lower individual cutter loads.
What inspection method was used to verify the dimensional accuracy of CNC prototypes?
A Coordinate Measuring Machine (CMM) was used to probe critical cylindrical interfaces and mounting holes, verifying compliance with ±0.05 mm tolerance. A surface roughness tester also confirmed the raw finish met the Ra 3.2 baseline. These quantitative metrology steps ensured part accuracy before applying the black glossy anodized coating.
