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Thread: Surface Finishes by Tolerance

  1. #1
    Associate Engineer
    Join Date
    Dec 2018

    Surface Finishes by Tolerance

    Hi, I'm new to the forum.

    Years ago I found a handy chart where it stated the average surfaces finish by the tolerance of the feature. I've been looking in the internet, but I can't find any such chart again. Everything I'm seeing on the internet is finish range by a machining process. An example of what I'm looking for is:

    .005 = 125 RMA

    .001 = 64 RMA

    .0005 = 32 RMA.

    These are not the actual values, but rather my best guess. I was looking for a chart to validate.

  2. #2
    Administrator Kelly Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    Surface finish and surface size or form are not inter-changable.

    For example;

    One can have an Ra of 250 micro inches and a flatness of .0002".

    Ra of 8 microinches and a surface size variation of +/- .040"

    Surface roughness is independent of form and size and are NOT interchange-able - ever..,
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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