Assumed Straigtness or Flatness
Assumed Straigtness or Flatness
(OP)
Hello, I'm having a debate with others to interpret the assumed flatness or straightness on a thickness or "bow" callout. The spec is Ansi 14.5M-1982. The thickness callout is .2787-.2745. Do I get RFS and the measured "bow" or do I have to place the part down and the entire form has to fit within the maximum of the tolerance. Thanks, Rich





RE: Assumed Straigtness or Flatness
Is it a flat part, or curved into a "bow" shape?
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: Assumed Straigtness or Flatness
RE: Assumed Straigtness or Flatness
RE: Assumed Straigtness or Flatness
RE: Assumed Straigtness or Flatness
RE: Assumed Straigtness or Flatness
RE: Assumed Straigtness or Flatness
I brought that specific question up when I took my GD&T course. Your assumption makes a lot of sense, but it is wrong as per ASME Y14.5M-1994. I am not 100% certain about the 1982 version of the specification.
According to ASME Y14.5M-1994, the thickness specification is the thickness at the point measured. It has nothing to do with flatness. If you want flatness, you must specify it.
JHG
RE: Assumed Straigtness or Flatness
RE: Assumed Straigtness or Flatness
I suggest upgrading to ASME Y14.5M-1994.
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: Assumed Straigtness or Flatness
For anyone who is interested. In Modern Geometrical Dimensioning And Tolerancing by Lowell W Foster along with the National Tooling and Machining Association or NTMA, the following was stated:
Rule 1 - Limits of Size Rule. Where only a tolerance of size is specified, the limits of size of the individual feature prescribe the extent to which variations in its geometric form as well as size are allowed.
It continues later in the same rule: The surface, or surfaces, of a feature shall not extend beyond a boudary (envelope) of perfect form at MMC. This boundary is the true geometric for represented by the drawing. No variation is permitted if the feature is produced at its MMC limit of size.
Chris We're a machining job shop and the prints states the specification. We cannot change it unfortunatly
Thank you all
RE: Assumed Straigtness or Flatness
Also (should be another thread) I'll bet the dwg states ANSI Y14.5M-1982, but all GD&T is per ASME Y14.5M-1994. Very common.
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: Assumed Straigtness or Flatness
by the 1994 version, even if prepared and stated to the 1982 version?
RE: Assumed Straigtness or Flatness
I referred to the 1994 standard because that is what I keep lying around. If drawings are prepared to the 1982 standard, they should be interpreted to the 1982 standard.
JHG
RE: Assumed Straigtness or Flatness
My experience with military design, whatever is called out, you follow that standard. It will be checked.
I am looking to see if/where it is written.
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: Assumed Straigtness or Flatness
RE: Assumed Straigtness or Flatness
Most people on the shop floor will just measure the thickness and that is it - nothing else unless you specify straightness or flatness, etc.
To confirm that the thickness does not exceed the form of .2787 (MMC) , one would need 2 parallel planes of .2787 apart which is MMC. Measure the thickness of the part (micrometer) and then make sure that it goes between the 2 parallel planes.
Hope this helps.
RE: Assumed Straigtness or Flatness
Just curious, but when was the drawing being discussed prepared? Do you have confidence in it being in conformance with the stated version of Y14.5?
RE: Assumed Straigtness or Flatness
I have no idea when this drawing was prepared. From what I understand we have been making this part for a couple of years and to dingy2's point we have not considered this up until this time. The only reason it even came up is that there was gross curvature on a part (rocking on the surface plate) and it raised some flags. We dug in to it and found we haven't been checking this feature correctly all this time. Functionally I think we're OK. Perhaps the designer didn't consider it either or we just lucked out.