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mechantaeus (Mechanical) (OP)
23 Feb 05 15:40
I am working with a vendor who wants to spec out the folowing :

1,5 mm/2 m Flatness
1,5 mm/2 m Straightness

I think calling out flatness and striaghtness this way is wrong . any ideas?



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Helpful Member!  type26owner (Mechanical)
23 Feb 05 16:00
Normally invoked as a slope refinement specified as a second callout. This is a common way to control the waviness within the total tolerance control which must have an equal or bigger envelope. Useful if the part can stand to be warped but not rippled.
Helpful Member!  ctopher (Mechanical)
23 Feb 05 16:21
is OK.
But use "-", not "/". Can be mis-read.

Sr. Mechanical Designer, CAD
SolidWorks 05 SP0.1 / PDMWorks 05
ctopher's home site

ringman (Mechanical)
23 Feb 05 19:08
Is Y14.5 applicable to the drawing?
Helpful Member!(4)  GDTGUY (Aerospace)
24 Feb 05 9:06
The flatness and straightness specification is being applied on a "per unit" basis.  The flatness and straightness can vary 1,5mm over any 2m area.  The concept is illustrated in ASME Y14.5M-1994, paragraph for straightness and for flatness.  The "/" between the values is correct.  Also, there is usually an overall specification applied with a "per unit" specification to prevent significant accummulation of tolerances over the total length and width of the part.  This effect is illustrated in ASME Y14.5-1994, Figure 6-5.

If these two specifications are being applied to the same surface, there is no need to have both.  Since they are both of the same value, the straightness specification (2D tolerance) will already be controlled as part of the flatness specification (3D tolerance).  The straightness specification would only only be useful if it refined the straightness to something better than 1,5mm/2m.

Helpful Member!  ewh (Aerospace)
24 Feb 05 9:22

Thanks for another clear explanation!  It deserves a star.
ctopher (Mechanical)
24 Feb 05 10:33
...Y14.5 is applicable to all drawings.

Sr. Mechanical Designer, CAD
SolidWorks 05 SP0.1 / PDMWorks 05
ctopher's home site

ewh (Aerospace)
24 Feb 05 11:52
  Y14.5 is only applicable if stated on the drawing.  GD&T has been used on drawings before there even was a Y14.5 standard.  That is why it is important that the standard and year of release be noted.
ctopher (Mechanical)
24 Feb 05 12:25
I agree, but it should be stated on all dwgs. Which usually isn't followed anyway.

Sr. Mechanical Designer, CAD
SolidWorks 05 SP0.1 / PDMWorks 05
ctopher's home site

ringman (Mechanical)
24 Feb 05 15:46
There seems to be some confusion with regards to the use of Y14.5.  According to what I read, It must be noted on the drawing or some other  document referenced on that particular drawing.  It IS NOT TO BE ASSUMED applicable.
mechantaeus (Mechanical) (OP)
25 Feb 05 9:39
Thank you all , I think I have a better understanding now, each one of you deserves a star.



Work Hard and Work Smart

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