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Thread: GD&T callout for sharp edge

  1. #1
    Associate Engineer
    Join Date
    May 2018

    GD&T callout for sharp edge

    Hi folks,

    I am working on a cylindrical ceramic part that has a hole in it. The sharpness of both the inner edge of the hole and the outer edge of the ceramic part are critical to the function of this part, and they are not guaranteed - the nature of the ceramic material means that these edges are quite likely to develop chips during initial machining. I'd like some way to mandate that these edges deviate from an ideal circular profile by no more than X. Here's what I've thought of so far:

    1. Define a very tight flatness tolerance for the end of the part (the face the contains both the inner and outer edges)
    2. Specify a surface finish tolerance on the end of the part, as well as on the inner and outer diameters. This idea was suggested by someone else (credit where credit is due).
    3. Apply a line profile control to the inner and outer edges. Intuitively, this feels like the way I'd want to do this - basically, define a swept cylinder along the ideal edge with radius X which the edge cannot deviate from. However, my reading indicates this isn't a valid use of this control.

    We use ASME Y14.5-2009. Any thoughts about which of these is best - or alternative suggestions - are very welcome. Thanks very much!

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    Ceramics are typically ground machining and machining chips do not form. Sharp edges are rarely actually required unless one is making a knife.

    Any of the dimensioning and tolerancing standards works, however if you're in the USA and are manufacturing in the USA or typical supplier countries I suggest ASME Y14.5-2009 and for the EU use ISO 1101.

    Ultimately, you should consult with a manufacturer or knowledgeable manufacturing person or engineer whom is familiar with the materials you are using in your end item design.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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