Engineer looking to better understand surface finish / roughness and how to specify values on a drawing.
At the company I work at, we generally trust our own machine shop to be able to use proper judgement when machining parts and generally do not specify surface finish unless it is a special part that falls outside of what they might expect, or if it is a part that requires specifically close tolerances.
However for parts that we send out to be made elsewhere, generally mostly stainless steel tanks, we are often asked to specify these values.
I am looking at charts and pictures, but am having a hard time getting a feel for what each value or range of values corresponds to.
Let's say I am fine with a standard "finish pass" on a lathe for a turned part. It doesn't need to be polished or anything special, but I want to make sure it isn't too rough to prevent easily mating. What finish should I specify?
Another example:. Let's say I have a boss that takes the load from a bolt that would otherwise loaded in shear. Boss goes into a machine hole. F7/j6 fit for example… What finish should I specify?
Lastly, let's say I have a gusset or something with a cutout in the middle to remove weight. Since it had no impact on anything, I am OK with the "as cut" finish from a plasma torch, as long as the dross is removed (which is standard practice for us anyway).
Submitted June 01, 2017 at 01:24PM by KingMango
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