Interpreting a Edge Profile Feature Control Frame for Inspection

[Ladykiller]

Okay, I've got a question that I can't seem to get a straight answer on in regards to an edge profile feature control frame in regards to inspection and reporting the data.

First off, my feature control frame is shown in the attachment. It points to the edge of the part and says ALL AROUND underneath it.

The tolerance in the feature control frame is 0.7 and I know that translates to +/- 0.35 and we will measure to three decimal places for accurate inspections.

So here's my question:

How do I correctly report the measurement data? For instance, if the part measures 0.37 from nominal, do I multiply it by 2 to put it in the terms of the feature control frame (similar to true position of a hole)? By doing this, the measurement becomes 0.74 and then when I apply rounding and significant figures, the measurement drops to 0.7 and is in tolerance and not a rejectable condition. Is this correct?

Another scenario would be -0.39 from nominal which would then in turn result in 0.8 (per the previous thought process) and be a rejectable condition. I would write it up as 0.8 in regards to the feature control frame, but I would also note that it is -0.39 out in the X direction for example.

For things like true position of a hole, this is relatively easy. Surface and edge profiles are a bit harder, especially when the sig figs and round off come into play. The round off and sig figs can hurt and help me at the same time.

 

[ewh]

forum1103 may be a better forum in which to ask.

I disagree that significant figures enter into the problem. Tolerance zones are absolute limits, and .35000001 would still violate the profile tolerance (assuming accurate measurement can be made).

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[Ladykiller]

We've got a spec to cover sig figs and that issue, so your point is moot.

 

[ewh]

My second one perhaps; the first still stands.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ewh]

I take that back... forum286 would be a better place to ask.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[tbuelna]

Ladykiller,

Your profile tolerance is a surface profile (3D) as opposed to a line profile (2D). The profile tolerance band specified can be equal unilateral (all+ or all- 0.7 in your example), equal bilateral (+/-0.35 in your example), or unequal bilateral. Unless otherwise specified, it's usually assumed to be equal bilateral.

The tolerance profile is determined by a normal offset from the 3D basic surface. Thus, depending upon the slope/curvature of the basic local surface in relation to the datums, the individual X,Y,or Z deviations may be substantially more than the tolerance limit.

As for rounding-off numbers in your favor, ANSI 268 specifically prohibits this. A measured deviation of 0.70001 would be out of tolerance in your example.

Hope that helps.
Terry

 

[ewh]

Thank you, Terry.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ewh]

I don't think he liked my response, and didn't even bother to read Terry's, last logging in the same day he joined.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[tbuelna]

ewh,

You can lead a horse to water......

Even if he did not agree with the responses, a simple thank you would have been nice. Unfortunately, a sense of anonymity seems to make some people forget their manners.

Terry