Aluminum anodizing thickness is one part of a finished-part specification. For a close-fitting hole, slot or mating surface, buyers also need the permitted dimensions after finishing. A coating callout by itself does not explain whether the finished component will fit.
Keep three records connected: the cutting drawing, the finishing instruction and the final inspection plan. Five checks help the cutting supplier, anodizer and buyer agree which dimensions belong to each stage. This guide concerns purchasing and handoffs; the responsible designer and finisher must approve the actual requirements.
Keep these requirements separate
- Coating thickness and finished-part dimensions need their own acceptance fields.
- Identify both surfaces when a dimension crosses a hole or outside width.
- Agree which supplier checks the part after the final finishing stage.
On this page
1. Separate aluminum anodizing thickness from dimensional change
The Aluminum Anodizers Council’s FAQ explains that anodizing converts aluminum into oxide. Total oxide thickness differs from the change at the original surface. Alloy, process conditions and other preparation steps affect the resulting dimensions. Obtain the proposed allowance from the chosen finisher rather than applying a universal growth percentage.
For procurement, put the finish requirement beside a separate finished-dimension requirement. Ask the designer to identify the controlling feature and the finisher to confirm the proposed process. Keep both responses with the approved drawing revision.
If an offer lists a film thickness but leaves final fit unresolved, mark that question as open. A supplier’s response to the coating field should not automatically close the dimensional field. This simple separation makes quotation reviews easier to follow.
2. State the units and specification basis
Write the unit next to the thickness value. One mil means 0.001 inch, which equals 25.4 micrometers. A mil is not a millimeter. Keep the original specified unit in the purchase record; if you add a conversion, label it clearly.
The AAC specification bulletin distinguishes coating thickness from coating mass per area. It also addresses alloy, temper and preparation when defining a finish. A weight-per-area result should not be entered as a thickness value without an approved interpretation.
Record the project specification, revision and the actual acceptance wording. Does the requirement apply to a minimum, a range or another stated criterion? Ask the specification owner to resolve an incomplete note. Do not select a value simply because it appears in an unrelated supplier catalog.
For drawings that mix inch and metric notation, use the same unit discipline described in our aluminum cutting in inches guide. Conversion helps communication; it does not create a new manufacturing tolerance.
3. Identify every surface involved in the fit
Mark the hole, slot or outside dimension on the drawing. Identify the mating component and the surfaces that determine the fit. A broad finish note may leave the team unsure which features require a separate dimensional review.
Where opposing surfaces are involved, the dimensional change must account for both. Some areas can be masked; the finisher should confirm the proposed coverage. These points are discussed in the AAC FAQ. Show any requested masked region explicitly instead of assuming that all holes will be treated alike.
Ask the designer to approve the finished fit and the relevant drawing note. The purchasing team can gather that decision, but should not turn a photo of an assembled frame into a clearance requirement. Record any unresolved interface before releasing the order.
Separate the coverage question from the assembly question. “This face is masked” describes the planned treatment. “This mating part fits” requires the agreed dimensional or functional check. Keep the two answers attached to the same feature reference.
4. Label dimensions before and after finishing
A cutting drawing may describe a supplied blank, while the assembly drawing describes the finished component. Name the stage in each inspection record. Otherwise, the same dimension can be copied into two documents even though the acceptance conditions differ.
For a cut-stock order, specify what the cutting supplier must deliver and what the next processor receives. If finishing is performed elsewhere, list that handoff. The cutting quotation should make its supplied stage clear rather than imply approval of work outside its scope.
Keep the cut-end condition visible in the planning conversation. Our anodized aluminum cutting guide covers existing finish, new cut faces and handling. This article addresses the separate question of dimensional requirements around finishing.
A later process change should return the affected requirements for review. Update the drawing or approved instruction first, then confirm which supplier needs the revised file. Avoid leaving an old allowance in a spreadsheet while the purchase order references a newer finish.
5. Assign the inspection location and responsibility
Use separate entries for a coating result and a finished dimension. The AAC FAQ lists coating-thickness testing with eddy-current instruments among finish evaluations. That is a different question from checking the width or diameter of the complete part.
Ask the inspection owner to define the required method, measurement locations, acceptance limits and reporting format. Record the instrument identity where the inspection plan requires it. A general photograph of a tool beside a part does not supply those details.
Agree who reviews each result and who releases the shipment. If the cutting supplier checks the blank and the finisher checks the finished coating, identify who confirms the final mating dimension. A completed blank check should not be copied into that final release field.
A fictional two-surface example
Suppose a fictional planning sheet defines an approved net outward dimensional allowance of 0.010 mm at each of two opposing surfaces. This is an invented arithmetic input, not a recommended anodizing value or a prediction for a real process.
| Fictional feature | Change from the stated allowance |
|---|---|
| Outside width across two treated faces | Increases by 2 × 0.010 = 0.020 mm. |
| Hole diameter across two treated sides | Decreases by 2 × 0.010 = 0.020 mm. |
| Coating thickness field | Cannot be filled from this dimensional allowance alone. |
The calculation explains the two-surface bookkeeping only. It does not choose a starting size, approve a fit or establish an actual film thickness. For a real component, the designer and finisher must agree the process-specific allowances and inspection requirements.
If the fictional hole starts at 10.000 mm, the stated allowance would give 9.980 mm in this simplified calculation. Whether that dimension is acceptable depends on the approved finished-part requirements. Arithmetic alone cannot answer the assembly question.
An order record that travels with the parts
Create one feature record containing the part number, drawing revision, feature reference, supplied stage, finishing instruction and final dimension requirement. Add the identified coverage regions, the finisher’s allowance confirmation and the inspection owner.
Keep coating acceptance and dimensional acceptance as separate status fields. If one is complete and the other remains open, the record should show that clearly. Include any approved changes rather than relying on a verbal explanation during shipment.
For a cutting review, send JiurunCut the profile drawing, required lengths, quantity and supplied-stage requirements through the contact page. Include the downstream finishing constraints that affect the blank. Confirm the scope of the proposed cutting work before treating it as finished-part approval.
Buyer questions
Does a coating callout replace a finished hole dimension?
No. Keep the coating requirement and the hole’s final acceptance requirement in separate fields, connected to the same drawing feature. Ask the responsible parties to resolve any conflict before ordering.
Can a caliper photograph confirm aluminum anodizing thickness?
No. Ask for the agreed coating test record, method and locations. The illustrative images in this guide are not measurement evidence for a real coating or batch.
What if the quotation covers only cut blanks?
Make that supplied stage explicit. Keep downstream finishing and final-fit decisions with their designated owners, and state the blank requirements needed for the next handoff.
Should the buyer choose a universal allowance?
Request a documented allowance review for the actual material, process and feature. Use an approved project requirement rather than transferring the fictional numbers above into a production order.