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Thread: Surface Finish

  1. #1
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    Surface Finish

    Hello, I've been browsing this forum for the last year or so when I first became a QA Engineer. This is my first post, so please let me know if there is any info I can provide.

    Background:
    We are familiar with surface finish testing and have been doing it for years for other customers, but they provide all the details we need: Ra μm Max., Cutoff Length (λc) and the standard such as ASME B46.1-2002.

    Problem:
    A potential new customer of ours has a Surface Finish callout of Rz 5 μm Max. in two locations on a part. See attached. There is no standard referenced on the print. The standard that we typically use ASME B46.1-2002 does not include Rz that is being used on the print, so we found ISO 4288:1996.

    1. We had to figure out what Cutoff Length (λc) to use. We figured on 0.8 based on the table provided in ISO 4288:1996. Is that correct?

    2. The larger surface finish callout says "min23". Does this mean that the entire surface within that zone needs to pass the surface finish test? If so, how do we test that whole area if we are only checking 0.8 λc based on the standard?

    I hope my questions are clear enough. Thank you for the help!
    Attached Images Attached Images

  2. #2
    Administrator Kelly Bramble's Avatar
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    Yes, ISO 4288 is most likely correct though know that your German speaking customer is most likely referring to DIN EN ISO 4288.

    Rz is the mean roughness depth and is measuring the total height or vertical distance from the highest peak to the lowest point or valley within a minimum of five sampling lengths, then averaging the peak-valley depths. This is not the same as Ra. Also, a Rz 5 is a aggressive manufacturing process, which may require honing, lapping, grinding or similar to achieve. My notes are based on the specified area and access to facilitate the manufacturing process should be considered.

    "min 23" specification is not shown within your attachments so I'm guessing this is an Ra specification? If so the requirement is simply that the roughness should not be less than Ra 32 - probably Gasket surface of equivalent.
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  3. #3
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    Hi Kelly, Thanks for the quick response! These parts are stamped metal components, so our goal is to meet the Rz 5 requirement without a secondary process. We are measuring other similar components that we make right now to determine our capability to do so. This led us to questioning exactly how this customer will expect the measurement to be taken.

    Quote Originally Posted by Kelly Bramble View Post
    "min 23" specification is not shown within your attachments so I'm guessing this is an Ra specification?
    I tried to attach the file 20190214_081136-vert.jpg Did it not appear? Sorry I'm new to posting.

    20190214_081136-vert.jpg
    Last edited by vailmij; 02-14-2019 at 09:03 AM. Reason: Typo

  4. #4
    Administrator Kelly Bramble's Avatar
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    OK, I see the "min23" specification that's just indicating the depth part of the area requiring the surface roughness. The Rz is specified is a partial surface area.
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    Quote Originally Posted by Kelly Bramble View Post
    OK, I see the "min23" specification that's just indicating the depth part of the area requiring the surface roughness. The Rz is specified is a partial surface area.
    Thanks again! So, the "min23" is just the area in which the Rz reading must be 5 μm Max. To clarify, if we take the measurement with cutoff length 0.8 anywhere within that area, then the part meets the spec?

  6. #6
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by vailmij View Post
    Thanks again! So, the "min23" is just the area in which the Rz reading must be 5 μm Max. To clarify, if we take the measurement with cutoff length 0.8 anywhere within that area, then the part meets the spec?
    Yes, you need five areas of length 0.8 mm for Rz 5.
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  7. #7
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    Quote Originally Posted by Kelly Bramble View Post
    Yes, you need five areas of length 0.8 mm for Rz 5.
    OK thank you so much for the clarification. My understanding is that the Surface Finish Tester (Mitutoyo SJ-410) automatically uses the 0.8 λc value to create 5 sampling lengths for a total of 4mm [0.8 x 5 = 4] per the attached table.

    So, the part will only need to be measured once within that "min23" area to determine if it meets the spec < Rz 5 μm ?

    Could you please confirm if I have understood this correctly? There is surprisingly very little information around the web to describe the exact method of measuring surface finish and the manual that came with the equipment doesn't answer these questions either.

    Thank you!

    Steps for roughness measurement EN ISO 4288.jpg

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