"BASIC" Dimension tolerance in First Article Inspection Report-continue

[UchidaDS]

thread1103-355263
Hi,

This is related to the old post. I lost the previous attachment somehow...Arrrgh!
Please see attachment.
These two dimensions has to be reported but want to know what is consider out-of-spec or within spec:

1. Dia. 2.000" ==>UL: 2.000+.004*2 = 2.008"
LL: 2.000-.004*2 = 1.992"

2. Height .700" ==>UL: .700+.004+.0035 = .7075"
LL: .700-.004-.0035 = .6925"
Am I right?
And what should I do with the "ALL REATURES SHOWN TO BE CONCENTRIX MUST BE WITHIN .010" TOTAL RUNOUT."?

Thanks!

 

[Belanger]

Where to start....

Spelling aside, the bottom note doesn't make sense because we don't know the datum for this total runout spec. Slapping a note about total runout being .010 is incomplete.

Then, on the diameter of 2.000, we must realize that the profile tolerance is unilateral, meaning that all of the .008 is inside. Therefore, the max diameter is 2.000 and the min is 1.984. We know this is unilateral because the phantom line shows the profile tolerance all displayed on the one side.
Also, remember that the profile requirement isn't merely a simple caliper/mike check across there, but it includes the form (roundness) and orientation (perpendicular to A) and location (coaxial with B) aspects. So those ideas should also be captured in the measurement being taken.

For the height, the nominal of .700 gets the same profile tolerance (all upward), so the max height is .708. The min is .700. (The flatness spec of .007 means that some local-size checks of the height could be as small as .693, but the mating envelope must always be within the range of .700 to .708.)

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

 

[pmarc]

J-P,
Are you sure this is the phantom line? To me this rather looks like a chain line - so in fact the line does not show the distribution of profile tolerance zone about true profile, but the area where the profile tolerance applies.

So the numbers for meaningless local two-point size checks are:
1. 1.992 and 2.008.
2. .689 and .704.

The bottom note reveals a simple fact that for the author of the drawing the phrase "unambiguous drawing specification" means almost nothing.

 

[UchidaDS]

pmarc: how is the .689 comes from?

 

[pmarc]

.689 = .700-.004(half of profile tolerance)-.007(flatness tolerance)

 

[Belanger]

pmarc -- I wondered that too, but made the call based on the leader. Notice in fig. 6-47 of the 1994 standard that the leader should touch the solid surface if using a chain line to merely show the length of tolerance coverage. Yet for a unilateral tolerance in fig. 6-15 the leader terminates at the phantom line. (And it has an opposing arrow, which our example didn't.)

Since the given drawing doesn't technically follow the standard in those admittedly minor details, it's a little bit up for grabs.

Seeing that unilateral tolerancing is less common, I'm willing to go along with the idea that it's merely showing the start/stop. In that case my numbers would be the same as what you give.

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

 

[Tarator]

Shouldn't that .030 dimension, which shows the start/end point of the profile call-out, basic?

 

[UchidaDS]

pmarc,Belanger : Is this how the number come from?
Please see attachment.

Appreciate the help!

 

[Belanger]

Yes. Since the bottom-most points create datum A to which the profile tolerance looks, the flatness of .007 is all on the "up" side.

And, yes I think Tarator's comment makes sense -- since that is just a gaging point, its dimension of .30 would be basic.

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

 

[pmarc]

What J-P said.

And I think your illustration pretty nicely shows why trying to think about profile tolerance in terms of single number is not good idea. The .689 as a local two-point size check can occur only in the small portion of nominal distance .700 containing opposed elements. The rest of the upper face simply has to fall within profile tolerance zone located relative to datums.