FAI and ANSI Y14.5 Trailing Zeros and Print Tolerances

Brad Gover

Involved In Discussions
#1
Hi everybody! I hope I am posting this thread on the right Forum. I have a question in reporting a measurement point on AS 9102 forms. The print calls out for a diameter of 0.302" +/- 0.005". Our inspection plan requires the use of a CMM to measure the diameter. The CMM reports out the diameter to be 0.307005". The inspectors are labeling this as Fail. The print requires 3 significant figures and I am wondering if I should report this to 0.307". I have not found any documentation requiring trailing zeros or reporting out data to the resolution of the instrument used to verify part conformance to print. Can I have the CMM programmer report out data to 4 digits and round to three digits?
 
Elsmar Forum Sponsor

John Predmore

Quite Involved in Discussions
#2
I personally would report results with same number of decimal places as the dimension and/or tolerance, plus 1.

The added precision of one place communicates to the customer whether your company rounds up or truncates to conclude a dimension falls inside or outside a tolerance band. The extra place of precision is consistent with one version of the Rule of Ten to One (see below). Because of measurement uncertainty, a precision of millionths of an inch is little guarantee that a measurement taken in millionths is accurate or repeatable. A CMM is notorious for measuring very precisely, but CMM results for a diameter will vary based on number of sample points, whether the diameter is best-fit or inscribed/circumscribed circle, where on the cylinder the points are taken.

Can someone please clarify the Rule of 10 to 1, what it is exactly, what I use it for, and so on? An example would help.
A more thoughtful answer to your question would to be guided by an understanding of the criticality of the dimension/tolerance. My assumption is the customer's part drawing communicates criticality in the number of places of the dimension/tolerance. If the customer truly wanted .307005" to be rejected, the customer should have communicated this with a print dimension of 0.302000 +/- .005000".

Of course, if your first article parts are in the region of 0.307005", you would be wise to take rapid action, or soon your parts will measure 0.3075" or above, and your process yield will deteriorate to unacceptable rates.
 

Jim Wynne

Staff member
Admin
#3
This subject has been discussed before, but this is a bit of a special case, I think. First, we should not assume that a customer is trying to communicate in code with their drawing specifications. .302 ± .005 means that .307 is the high limit, no matter how many decimal places you add. .307005 is > .307, so the high limit has been exceeded.

As John Predmore has pointed out, measuring diameters is a tricky business, because there is a theoretically infinite number of diameters that can be measured in any given cylinder. You should never measure hole size with a CMM unless roundness is a concern. Furthermore, the chances are vanishingly small that the sixth decimal place is important. It's common to measure such holes with gage pins of the "minus" variety (actual size being .0002" smaller than nominal) and then report the size of the largest pin that will fit in the hole. Another option is just to report the hole size at the high limit. IMO, the problem here is (a) not making sure that the size is comfortably away from the tolerance limits in production and (b) using the wrong measuring device.
 

dsanabria

Quite Involved in Discussions
#4
After considering the requirements of the print .302 +/- .005 - first is not a critical dimension, second how many points did you take, third, what is the roundness and fourth what is the temperature of the material / environment.

Train the oprator to think outside the box, incorporate all te factors and make a decision. it is.307 with i n tolerance - in the future is a plug gage
 
Thread starter Similar threads Forum Replies Date
Q Change the shape of the raw material FAI AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
P FAI Ballooning ASME Y14.5 AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
Q Full or Partial FAI? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
D Partial FAI - AS9102 - One single drawing has 10 part numbers AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
M AS9102B Detail Part/Assembly FAI Form 1 box 13; AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
A When there is a 2 year lapse in production, is a full FAI required? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
M When is FAI required? AS9100 8.5.1.3 and 8.4.3 requirements AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 9
M AS9102 FAI Report formats - Boxes in form 1, 2, 3 of AS9102 AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 4
A AS9100D FAI requirements needed? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
R AS9100 DELTA FAI - Sub-supplier for plating changed AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
D AS9102 - Assembly FAI for Use As Is or Repaired Parts AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 6
A AS9102 Delta FAI Require after Rework stock item from stock AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
B AS9102 - Completing Partial FAI's for Baseline Part Numbers AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
K First Article Inspection (FAI) - Equipment used - Dimensions vs. Go/No-Go ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
E AS9102 FAI - What makes a COTS modified? (PCB assemblies) AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 11
C Is a First Article Inspection (FAI) Procedure required by ISO 13485? ISO 13485:2016 - Medical Device Quality Management Systems 3
B AS9102 FAI & Lower Level Drawings - How should we perform the FAI? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
P AS9102 full FAl or a partial FAI after production inactivity period AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
M FAI AS9102 - What does a First Article Inspection cover? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 11
ScottK Statistical basis for 30 pieces for FAI 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 7
U Whether First Article Inspection Report- FAI is mandatory for regular Human Factors and Ergonomics in Engineering 4
D FAI. Form 2, process or functional test? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 0
G FAI Objective Evidence AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
M FAI Requirements of Detail and Assembly AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 4
O AS9102 FAI report Forms 1-3 Document Control Systems, Procedures, Forms and Templates 6
J FAI per AS9102 affecting Fit, Form, Function AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 6
R AS9100 FAI - First Article Inspection to a prior Customers PO AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 7
R AS9102 FAI with No Drawings Supplied AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
G FAI (First Article Inspection) Responsibility - QC or Engineering? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 3
APHX02 AS9102 FAI Requirements that pertain to a Dimension 'delta' AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
R FAI (First Article Inspection) on source-controlled parts AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
K FAI (First Article Inspection) vs PPAP (Production Part Approval Process) APQP and PPAP 15
W Am I allowed to ship parts without FAI approval from the customer? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 6
G Is it mandatory to record all processes in form 2 of AS9102 FAI report AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 4
T FAI (First Article Inspection) of Large Assemblies/Tooling after move to new building AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 12
W Certification on AS9100C - FAI or PPAP? Project Management or APQP? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 11
Q FAI IAW AS9102 - First Article Inspection Documentation Question AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 20
D AS9102 B (FAI - First Article Inspection) is Released - October 2014 AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 12
G Plant Relocation - Is it necessary to perform FAI? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 13
A AS9102 First Article Inspection and NC Parts - New FAI? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
K Partial FAI on Semi-Complete Parts question ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 1
D AS9100 FAI Form for Plating Document Control Systems, Procedures, Forms and Templates 7
B Lockheed Q2R Revision 10 FAI Planning Example AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
WCHorn AS9102 Paragraph 5.3-5 - Lapse in Production - FAI Requirements AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 9
P New to AS9100 Rev. C - Setting KPIs and FAI Reports AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 14
V Printed Circuit Board Assembly and Components FAI Question Document Control Systems, Procedures, Forms and Templates 8
D Delta or Partial FAI (First Article Inspection) - What are the differences? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
K What is Quality's and Engineering's role within FAI's AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 6
K FAI (First Article Inspection) using Digital Design Data AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 7
J FAI for Heat Treated Details - Inco Parts Shrink AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2

Similar threads

Top Bottom