Straightness ??

You need to attach the drawing.

That should be the picture attached .

Thanks

Ross

Is the embedded drawing defined based on the ASME or ISO. I cannot find a clear answer on either of the two discussions you started.
(
Please let us know.

I suspect it's ASME, therefore DMPF (derived median plane flatness) is the inquired callout.
if that's the case the best way to check shown straightness is with a gage:
size of the gage: 42.00 - 0.010 - 0.020 = 41.88 (if I am doing the math correctly)

DMPF nullifies rule#1, so the gage size is smaller than the one (than the gage) you would have been checking with, if the straightness was not shown (42 - 0.1 = 41.9), thus accepting more (hopefully) functional parts.

What greenimi may have hinted at but did not say explicitly - no, it is not a valid specification. You may specify the straightness of line elements of a single planar surface, flatness of a single planar surface, or flatness of the Derived Median Plane of a pair of planar surfaces (DMP Flatness). There is no option for DMP straightness.

I too suspect that DMP Flatness is the actual desired callout.

If the drawing is per ASME, what version of Y14.5 exactly is it to? If, by any chance, it is '94 then this callout is legal and applies to the derived median plane of the width (see para. 6.4.1.1.3 in Y14.5M-1994).

Nice catch, pmarc. I almost forget it.


Season

Thank you pmarc.
I assumed it's 94, but I run too fast to answer the OP question without thinking it too much.