QUESTION: Is there an industry standard for rotational tolerance of an angled ferrule (APC) face with respect to a key on the ferrule carrier or connector body. Or do manufacturers just strive for a minimum. What are typical figures?
ANSWER: With APC ferrules, the Apex Offset value is actually the resultant of two vectors—–the “horizontal” axis offset (the offset due to actual end-face angle error) and the “vertical” axis offset (the offset due to rotational error of the ferrule relative to the key—-“key error”). That is, if the actual Angle of the APC ferrule is exactly 8.000 degrees, then any Apex Offset value is 100% due to Key Error. Conversely, if the actual Key Error of an APC connector is exactly zero, then any Apex Offset value is 100% due to angle being greater than or less than 8.000 degrees.
So, some manufacturers simply use Apex Offset as the only pass / fail specification when measuring angles, and ignore the Key Error value. It’s really up to the manufacturer. I understand this from a production point of view—–after all, Apex Offset DOES have industry-accepted specifications, so if my product fails for Apex Offset, what difference does it make if it’s because of Angle error or Key error or both?
My answer to that question is: if you want to improve your APC Apex Offset values, it’s critical to understand which aspect——Angle Error or Key Error—is creating the majority of the Apex Offset. The causes of Key Error are completely different from the causes of Angle Error. Often, the Key Error is simply due to the ferrule not sitting properly within the connector body, and has nothing to do with the polishing process—-simply springing the ferrule up and down a few times will “seat” it properly within the connector, and re-measured Key Error values fall to near zero. This is in contrast to Angle Error values, which are almost always the direct result of the polishing process itself and requires re-polishing to fix.
So, while “Industry Spec” for Key Error may not exist, monitoring Key Error is very important when troubleshooting / improving Apex Offset results.
You should always strive for a minimum of key error, but you don’t want to handcuff yourself and rework product that meets Apex Offset specifications. If your customer is requiring a specification on Key Error, a common spec value is +/- 0.5 degrees—-because at this point, even with a zero Angle Error, the Apex value will almost certainly also fail Apex Offset specifications. But if it is not required, I would recommend to not use Key Error as a pass / fail spec in production, and rely only on the Apex Offset specification. However, I would certainly monitor and analyze all the geometry data—including Key Error—as part of my standard process control, striving to keep Key Error to a minimum and investigating causes if values rise.
Quick Links to APC Blogs include:
- Polished Connector Geometries, APC – Part I: https://focenter.com/polished-connector-geometries-apc-part-1/
- Steps to Overcome Common APC Polishing Issues: https://focenter.com/steps-to-overcome-common-apc-polishing-issues/
Answered by AskFOC Technical Team November 17, 2016
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