# Metal finishing: what's a "nice" waviness spec for a grinding shop?

**URL:** <https://boards.straightdope.com/t/metal-finishing-whats-a-nice-waviness-spec-for-a-grinding-shop/716620>\
**Category:** Factual Questions\
**Created:** [April 2, 2015, 2:18pm UTC](https://boards.straightdope.com/t/metal-finishing-whats-a-nice-waviness-spec-for-a-grinding-shop/716620 "2015-04-02T14:18:58Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\
**Post date:** [April 2, 2015, 2:18pm UTC](https://boards.straightdope.com/t/metal-finishing-whats-a-nice-waviness-spec-for-a-grinding-shop/716620/1 "2015-04-02T14:18:58Z")

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I know, it depends. I’m having some stainless plates ground to 8 microinches Ra for use in testing thermal conduction in various engineering plastics coming in contact with the plates. In my opinion 8 microinches is a nice smooth ground finish, but it’s not one that would be surprising or obscure in a typical machine shop or grinding shop. I think any shop that advertises they do industrial grinding would accept my order. But if I said 1 or 2 or maybe 4 microinches they’d say that had to be lapped or polished and maybe it would be a special thing I’d have to find a specialty shop for.

What I want to know is, what value of waviness is similarly at the nice end of what a grinding shop can do, but not obscure or special?

I don’t know what level of waviness or roughness is “required”. I’m a scientist studying this question, and what I lack is a feel for, or experience with, what’s practical to do with typical shops.

Thanks!

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**Author:** ![bubba001](https://avatars.discourse-cdn.com/v4/letter/b/f17d59/32.png) [@bubba001](https://boards.straightdope.com/u/bubba001)\
**Post date:** [April 2, 2015, 9:38pm UTC](https://boards.straightdope.com/t/metal-finishing-whats-a-nice-waviness-spec-for-a-grinding-shop/716620/2 "2015-04-02T21:38:16Z")

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I think you need to think in terms of 2 specs: Ra, which is the texture on the surface, and flatness, which is the contour of the surface.

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**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\
**Post date:** [April 2, 2015, 10:42pm UTC](https://boards.straightdope.com/t/metal-finishing-whats-a-nice-waviness-spec-for-a-grinding-shop/716620/3 "2015-04-02T22:42:34Z")

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Your best bet is to ask your vendor (or potential vendor). Particularly if you don’t have a good grasp on your requirements. It is unlikely a vendor would recommend requirements outside of their capabilities, and they may ask questions you hadn’t considered.