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Anonymous Poster #1

Difference Between Flatness & Straightness

12/12/2011 5:07 AM

HI,

Can any one tell me what is the difference between Flatness and Straightness.is it right to apply both flatness and straightness for same face?how to check for flatness and straightness?

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Anonymous Poster #2
#1

Re: GD & T

12/12/2011 5:16 AM

With regard to surface shapes, flatness = 1/bumpiness; with regard to linear shapes, straightness = 1/curviness. My apologies for such esoteric theory at an early stage.

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#2

Re: GD & T

12/12/2011 5:24 AM

Straightness is the 2-dimensional analog of flatness, which is 3-dimensional.

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#7
In reply to #2

Re: GD & T

12/12/2011 3:53 PM

That would be the way I interpret it.

Flatness is the degree of variation in surface height with regard to a reference 2D plane.

Straightness is generally the linear variation compared to a reference 1D strait line.

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Anonymous Poster #3
#3

Re: GD & T

12/12/2011 7:14 AM

No

Straightness is usually put on surfaces that aren't flat. It is used to control the straightness of a surface or an axis.it specifies how much the surface or axis is allowed to vary from the perfect straight line mentioned. Straightness tolerancing is usually applied on cylindrical features (shafts,bars etc.) to control bowing and other distortions. Of course it may also be applied to flat surfaces, when it would mean that each longitudinal element of the surface must lie within the tolerance zone specified, in the direction denoted. The straightess tolerance is some time put on the axis too (hole or shaft) but there the preferable would be the cylindricity.

Flatness anyway had to be on a flat surface.

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#4

Re: GD & T

12/12/2011 8:13 AM

Flatness is a 3D form control of the surface. Surface straightness is a 2D form control of the surface only applying to the view in which the straightness control is situated. For most 3D surfaces, the design requirement is usually that the entire surface be controlled, so flatness would be the tool of choice in controlling the variation.

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Anonymous Poster #4
#5

Re: Difference Between Flatness & Straightness

12/12/2011 1:41 PM

http://www.playtex.com/

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#6

Re: Difference Between Flatness & Straightness

12/12/2011 2:20 PM

Straightness is related to a line. Flatness is related to a plane.

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#8

Re: Difference Between Flatness & Straightness

12/12/2011 3:58 PM
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#9
In reply to #8

Re: Difference Between Flatness & Straightness

12/12/2011 4:58 PM

GA

To try to put it more accessible language;

Straightness is deviation from a (perfect) axis or edge.

Flatness is deviation from a (perfect) plane

E.g. the letter 'S' can be flat, but is not straight.

A 'straight road' is not flat.

Similarly, a tube or shaft, can be straight, but is not flat.

They can appear to occur together, but are applying to quite different aspects.

e.g. a 'D' shaped extrusion may have both flatness and straightness tolerances, as either could be 'off' independently of the other.

I.e. the terms are not interchangeable.

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#10

Re: Difference Between Flatness & Straightness

12/12/2011 10:38 PM

When I was a teenager I had a girlfriend who straight away told me she was flat. Has things changed since then? ....being a long time now maybe, new technology....

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Anonymous Poster #1
#11

Re: Difference Between Flatness & Straightness

12/13/2011 12:14 AM

How do we check for flatness and straightness?

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#12
In reply to #11

Re: Difference Between Flatness & Straightness

12/13/2011 7:37 AM

Surface plate, dial indicator, laser, CMM, any number of ways.

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#16
In reply to #11

Re: Difference Between Flatness & Straightness

07/01/2024 8:05 AM

Dunno. It can't be seen from here. Posting pictures might help.

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#17
In reply to #16

Re: Difference Between Flatness & Straightness

07/07/2024 7:47 PM

I take my hat of to you - trying to get a question clarified after 13 years !

This place is getting surreal. I just noticed an update to a question about chess that vaporized years ago. Not saying who, but it was posted by a stellar avian .

Shhh....

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#13

Re: Difference Between Flatness & Straightness

06/18/2013 11:27 AM

Dear Friend,

STRAIGHTNESS refers/applies to a LINE.

FLATNESS applies to a surface with out undulations.

DHAYANANANDHAN.S

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#14

Re: Difference Between Flatness & Straightness

06/18/2013 1:12 PM

You see a woman with no "boobs" - this is Flat and if she is not crouched then - this is straight. This then defines both and you you cannot use them together as same.

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#15

Re: Difference Between Flatness & Straightness

11/19/2013 12:50 PM

For simple explanation let us take two coke bottle...Put these two coke bottle in straight.i.e (2 coke bottle should lie in same axis-collinear)... Deviation in the axis of two bottle is known as straightness error....In a same way if u could see the bottle surface it is not flat...i.e(bottle seems to be some wavy nature(viewing plane))...

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