.006mm flatness 2

[farrell162]

I have a part that has a flatness call out of .0002in to itself and a .002in perpendicularity to datum A over the surface of a slot that measures .275in x .551in x .039in deep. Our customer says that the flatness is out by +.0002. I have tried to repeat that but I am having trouble with setting this up and to be able to check the flatness of this feature to itself. The perpendicularity to datum A is is good with in .0005 - .001 depending on the part. does anyone have any suggestions to help me out?

Thank You

Stephen Farrell
Quality Manager

 

[IRstuff]

Isn't perpendicularity typically called out as an angle? Is your definition tied to a measurement of runout over a distance to get the angle?

What is your question? Are you wanting help on how to make the measurement? Have you looked at a non-contact profilometer?

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I can do absolutely anything. I'm an expert!

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[KENAT]

Isn't perpendicularity typically called out as an angle? +> No assuming it's a properly applied GD&T perpendicularity control. Perpendicular is a band of specified width at exactly 90°.

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[IRstuff]

I guess I don't get it; without knowing where the center of the angle applies to a linear band, how do I even know whether some arbitrary linear measure means anything at all?

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[dgallup]

We have many small surfaces that have to be flat to a micron or two. We measure flatness using a Mahr Perthometer. You trace the surface in question then level the trace and pick the high and low points to find the flatness. It's really quite simple.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[KENAT]

IRstuff, feel free to ask these questions over in forum1103 not sure we're really helping the OP though.

http://www.gdandtbasics.com/perpendicularity/

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[Belanger]

Stephen,

Check out dgallup's reply. If you have a computerized device that can probe or scan a surface, then the flatness is just an absolute-value comparison of the high points and low points (peaks and valleys). It is not centered around anything, so there is no positive or negative connotation to the flatness reading. And there's no datum for flatness, so it ignores any tilt of the surface.

If you're stuck with more primitive inspection equipment, then flatness might be measured with a dial indicator, but since you said .0002 I hope you have a CMM or profilometer or perthometer (never hear of that one; it must be Mahr's trademark name).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[farrell162]

Thank you Belanger and dgallup for your input that's exactly what I thought. With our CMM and dial indicator I get the part good by aligning the part off that surface and probing it. I will have to get with our customer and see what method of inspection they are using I have a feeling its just visual. But again Thank You i just needed to know that what I was doing was the best way.

Thank You

Stephen Farrell
Quality Manager