Controlling Slot Dimensions and Surface Finish in a Black Anodized 6061 Aluminum CNC Plate

Project Overview

This project involved the production of a black anodized 6061 aluminum CNC plate for an Indian customer. The component featured a rectangular outer profile with rounded corners, repeated elongated slots, small hole features, and mounting holes distributed around the plate.

The confirmed manufacturing process included three-axis CNC machining, manual abrasive surface finishing, dimensional inspection, and black anodizing. A 0.01 mm tolerance requirement was included in the project information, although the specific feature controlled by this tolerance was not disclosed in the processed drawing.

The customer also visited the manufacturing facility to inspect the component and discuss tolerance control and anodized surface requirements.

Based on the available background, the customer appears to be involved in custom automation equipment and may serve semiconductor-related applications. However, the exact installation position and final function of this component were not confirmed. This case therefore focuses on the verified manufacturing, finishing, inspection, and packaging requirements.

Part Requirements

The part was machined from 6061 aluminum and had a relatively flat plate geometry.

Its primary visible features included:

• A rectangular outer profile with rounded corners;
• Repeated elongated slots across the central area;
• Multiple small holes positioned near the slot pattern;
• Mounting holes near the outer edges;
• A broad external surface requiring a uniform black finish.

The combination of repeated slots, mounting holes, and a large visible surface meant that both dimensional control and cosmetic handling had to be considered during production.

Main Machining Challenges

One of the main manufacturing challenges was controlling the repeated elongated slots.

For this type of component, dimensional control is not limited to the width and length of each individual slot. The machining supplier may also need to control:

• Spacing between adjacent slots;
• Alignment of the slot pattern;
• Distance from the slots to the reference edges;
• Relationship between the slots and mounting holes;
• Burr condition around internal slot edges.

The exact drawing tolerances for these relationships were not disclosed, but they are typical engineering considerations for a plate with this geometry.

Another challenge was the flat plate structure. Removing material from multiple adjacent areas can change the stress distribution in the workpiece. Depending on the original stock condition, part thickness, workholding pressure, and machining sequence, this may contribute to local deformation.

The broad visible surface also required controlled finishing before anodizing. Uneven sanding pressure, residual tool marks, scratches, and inconsistent surface direction can remain visible after black anodizing.

Machining Strategy

The complete internal process sheet was not provided. The following section therefore represents a manufacturing analysis based on the confirmed three-axis machining process and the supplied production images.

A practical process for this geometry begins by establishing a stable primary reference surface. Datum edges can then be used to locate the repeated slot pattern, mounting holes, and external profile.

Where possible, geometrically related features should be machined from the same datum setup. This reduces the number of reference transfers and helps control the relationship between the slot pattern, mounting holes, and outer edges.

The repeated slots require controlled tool engagement and chip evacuation. Narrow slot geometry can trap chips and increase local cutting heat. Tool condition is also important because worn cutting edges can increase burr formation along the internal edges.

After the internal slots and holes are produced, the outer contour and edge features can be completed according to the selected setup sequence.

Where a 0.01 mm tolerance applies, the controlled characteristic should be clearly identified. A 0.01 mm requirement on material thickness, slot width, hole diameter, position, or hole spacing may require different machining and inspection methods.

After CNC machining, the photographs show manual abrasive finishing of the large aluminum surface. This operation was used to reduce visible machining marks and prepare the part for anodizing.

Abrasive finishing around slots and holes must be controlled carefully. Excessive local sanding can round edges, alter the appearance of machined boundaries, or affect small dimensional features.

Surface Finishing Considerations

The completed component received a black anodized finish.

The available project information does not disclose the anodizing type, coating thickness, gloss level, or color standard. These values should therefore not be assumed.

For similar components, the engineering drawing should clarify:

• Whether critical dimensions apply before or after anodizing;
• Whether any holes or functional surfaces require masking;
• Whether the slots have a mating or positioning function;
• Which surfaces are cosmetic;
• Whether a specific color range or gloss level is required;
• Whether contact or grounding surfaces must remain uncoated.

The final appearance of black anodized aluminum depends partly on the condition of the base material before treatment. Machining marks, sanding direction, local scratches, and handling differences may remain visible after anodizing.

For this reason, the surface preparation method should be agreed before production when cosmetic consistency is important.

Inspection and Quality Control

The project photographs show dimensional inspection using a dial caliper.

This confirms that dimensional checks were performed, but the complete inspection equipment list and inspection plan were not provided.

For a slotted aluminum plate, the inspection plan may need to cover:

• Overall length and width;
• Material or finished-part thickness;
• Slot width and slot length;
• Spacing between repeated slots;
• Hole diameters;
• Hole-to-edge distances;
• Mounting-hole relationships;
• External profile dimensions;
• Flatness, when specified;
• Burr condition;
• Anodized surface appearance.

A dial caliper can be used for certain general dimensional checks, depending on the feature and tolerance. However, a stated 0.01 mm tolerance should be reviewed individually to determine whether the selected measuring instrument provides sufficient resolution and measurement capability.

The customer drawing should remain the controlling acceptance document. Critical dimensions should be identified explicitly rather than relying only on a general tolerance statement.

Final Inspection and Protective Packaging

The new project photographs show the finished black anodized plates being handled in an area marked as a full-inspection area.

The images also show individual parts being separated with soft white protective wrapping before carton packing. This is an important consideration for black anodized components because direct contact between finished parts may create scratches, friction marks, or visible edge damage.

The verified packaging process shown in the photographs included:

• Separating individual components with flexible protective material;
• Arranging the wrapped parts at the inspection and packaging station;
• Placing the protected components into a cardboard carton;
• Closing and sealing the outer carton.

The available photographs do not confirm the use of antistatic materials, custom foam inserts, moisture protection, or a specific drop-test standard. These characteristics should not be claimed without additional packaging specifications.

For similar projects, the packaging requirement should be determined by part weight, surface sensitivity, quantity per carton, transport method, and customer handling conditions.

Manufacturing Result

The completed parts received a black anodized surface, and the final product images show the repeated slots, mounting holes, rounded external profile, and finished black appearance.

Dimensional checking was performed during production. The customer also visited the facility to inspect the component and discuss tolerance and anodizing requirements.

After final processing, the parts were individually protected and packed into cartons. This packaging arrangement reduced direct contact between the black anodized surfaces during handling and shipment.

No verified information was provided regarding production quantity, coating thickness, inspection yield, assembly performance, delivery time, or field performance. These results are therefore not claimed in this case study.

Engineering and Purchasing Takeaways

This case provides several practical reference points for engineers and purchasing teams sourcing similar CNC aluminum components.

First, a 0.01 mm tolerance should be assigned to a clearly defined functional feature. Applying the same tolerance broadly across the entire component may increase production and inspection complexity without delivering an equivalent assembly benefit.

Second, the drawing should define the datum system used to control the slot pattern, mounting holes, and external profile. A clear datum structure helps the supplier plan machining setups and select appropriate inspection methods.

Third, anodizing requirements should specify more than color. Buyers should confirm coating type, coating thickness, masked surfaces, cosmetic expectations, and whether functional dimensions apply before or after finishing.

Fourth, broad black surfaces require packaging protection. The quotation request should state whether parts need individual wrapping, separators, protective film, custom trays, or controlled quantities per carton.

Finally, buyers should provide the following information before quotation:

• Complete 2D drawing;
• Material specification;
• 3D model where available;
• Critical dimensions and datum references;
• Required quantity;
• Anodizing specification;
• Cosmetic surface requirements;
• Inspection requirements;
• Packaging and transportation requirements.

Conclusion

Producing a black anodized 6061 aluminum slotted plate requires coordinated control of CNC machining, slot and hole relationships, manual surface preparation, anodizing requirements, dimensional inspection, and final packaging.

The correct manufacturing method depends on more than the material grade. It must also consider the part geometry, datum system, functional tolerances, cosmetic requirements, coating specification, and transportation conditions.

For similar custom components, buyers should identify the critical dimensions, specify whether tolerances apply before or after anodizing, and define the required level of surface protection during packaging.

If you are developing a similar custom aluminum component, you can send us your drawing, material specification, required quantity, surface finish, critical tolerance requirements, and packaging expectations for a manufacturability review.