Tolerances before or after anodizing?

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Hey there,

I have a question regarding the standard practice in the industry about specifying tolerances in relation to surface treatments like anodizing. Given the potential for anodizing to add a few to tens of microns of material, which could impact the final dimensions and potentially lead to parts being out of specification, how is this typically handled? Is the norm to define part tolerances considering the expected film thickness from such treatments, ensuring the final dimensions fall within the desired specifications post-treatment? Or is it more common to specify the tolerances for the finished, anodized parts?

Thanks,

Nick

Résolu parMario Coppola

Ciao Nick,
for my experience I can only tell you: it depends.
We must admit that normally the treatment must be performed on finished product after all the working and therefore on precise dimensions.
With reference to the MIL-A-8625, I can tell you that the anodic oxidation type I and type II change the dimensions of the finished product by a few microns, but the anodic oxidation type III (known as Hard Anodizing) changes the finished size of the part and even modifies the roughness worsening it.

I believe it is necessary to define tolerances before and after this anodizing treatment, even the final roughness must be defined.

Keep in touch,

Mario Coppola

    • E

      Hey there,

      I have a question regarding the standard practice in the industry about specifying tolerances in relation to surface treatments like anodizing. Given the potential for anodizing to add a few to tens of microns of material, which could impact the final dimensions and potentially lead to parts being out of specification, how is this typically handled? Is the norm to define part tolerances considering the expected film thickness from such treatments, ensuring the final dimensions fall within the desired specifications post-treatment? Or is it more common to specify the tolerances for the finished, anodized parts?

      Thanks,

      Nick

      0
    • Xometry Engineer

      Hello Nick,

      It’s great to hear from someone with a keen interest in the intricacies of CNC manufacturing, especially when it comes to the nuanced area of specifying tolerances about surface treatments like anodizing. With over 16 years of experience navigating the complexities of manufacturing processes, I appreciate the importance of ensuring that every part meets the required specifications, even after finishing processes.

      Considering Anodizing in the Design Phase: It’s vital to anticipate the impact of anodizing on part dimensions early in the design process.
      This means:
       – Understanding the typical thickness added by the anodizing process you’re using.
       – Adjusting the initial dimensions of your parts to accommodate this thickness.

      Specifying Tolerances:
       – Pre-Treatment Tolerances: Some choose to specify the dimensions and tolerances of the part before anodizing, knowing the process will add a predictable amount of material.
       – Post-Treatment Tolerances: Others prefer to define the tolerances for the finished, anodized parts, ensuring that the final product, regardless of the added layer, falls within the desired specifications.

      Alternatives:
       – Design with Anodizing in Mind: Specify part dimensions and tolerances before anodizing but adjusted for the expected film thickness. This method requires a good understanding of how much material the anodizing process will add.
       – Final Dimensions Specification: Specify the dimensions and tolerances for the finished, anodized parts. This approach may offer more predictability for the fit of the final assembly but requires precise control and understanding of the anodizing process.

      Conclusion:
      Each method has its benefits and challenges, and the choice often depends on the specific requirements of your project, including the precision needed and the nature of the assemblies the parts will be used in. Feel free to ask more questions or seek clarification. I’m here to help and make sure the information is as accessible as possible.

      Best regards,

      Attila

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        Attila Szucs

        Thank you!

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      Xometry Engineer

      Hello Nick and Attila
      As a Production support engineer at Xometry, I could add that by default, when a drawing is submitted to us and an anodizing or other post-treatment is ordered, we consider that the tolerances are indicated AFTER treatment, as it would be difficult for us to know exactly the thickness obtained on all surfaces by our manufacturing partners and their anodizing partners. Our partners have then the responsibility to adapt the machining parameters accordingly.
      Happy to help
      Pierre-Yves

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        Pierre-Yves Huet

        Thank you, Pierre-Yves!

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    • A

      Hello there, so let me know if I understand correctly with this example. We consider making hard anodizing and indicate 15μ thickness on our drawing ; and determine our tolerance in accordance. Can we be sure that the manufacturer will adapt the machining parameters, to match with the anodizing thickness and after-processing tolerance ? 

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      • Xometry Engineer
        Alex

        Thanks for reaching out with a great question! Specifying a hard anodizing thickness of 15μ on your drawing is a solid start. Here’s the scoop: achieving exact thickness in anodizing can be a bit like hitting a moving target. We usually see a swing of about +/- 3 microns. So, if your tolerance is wide, like +/- 0.2mm, you’re in the clear. But for tighter spots, like an h7 hole, we go a bit oversized pre-anodizing and cross our fingers.

        The good news? Your manufacturer will tweak machining to align with the anodizing and keep your specs in check. For those precision-critical parts, let’s chat early to hatch a plan that nails your needs.

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    • Ciao Nick,
      for my experience I can only tell you: it depends.
      We must admit that normally the treatment must be performed on finished product after all the working and therefore on precise dimensions.
      With reference to the MIL-A-8625, I can tell you that the anodic oxidation type I and type II change the dimensions of the finished product by a few microns, but the anodic oxidation type III (known as Hard Anodizing) changes the finished size of the part and even modifies the roughness worsening it.

      I believe it is necessary to define tolerances before and after this anodizing treatment, even the final roughness must be defined.

      Keep in touch,

      Mario Coppola

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        Mario Coppola

        Thank you for the insights!

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