Comment by V__
3 years ago
I'm wondering why the tolerances for the oil pipe were so small in the first place. Why not make the pipe one or two mm thicker?
3 years ago
I'm wondering why the tolerances for the oil pipe were so small in the first place. Why not make the pipe one or two mm thicker?
It would add up weight wise, and it’s one of the simpler parts. Jet engines are high performance precise machines with many quickly spinning parts. If you can’t bore a tube correctly how are you going to machine a high efficiency, balanced turbofan system?
That said it seems like did have a poor process where a part could be out of spec and they had no good way to check it. As they mentioned about Swiss cheese, you want as many layers as possible, and checks like that are needed.
Because there are a zillion important parts on the airplane, if you make each one heavier than it needs to be, the airplane will be nailed to the tarmac.
That makes sense. Here’s the question I left the article with:
Why not counterbore the pipe before installation, so it’s a trivial process?
Would it then not survive welding perhaps?
Because its dead simple to machine a center and the designer did not factor in machinist/engineer/qa/facility incompetence.
You don’t need any such incompetence in this case, as explained in the article, though it does help and that specific facility had several issues. The tube was built to spec, it’s the specs that were not what they should have been.
The failures were more with the whole process (like the reference points with different tolerances and the inadequate paperwork) rather than machinist incompetence. They are just the guys at the bottom.
The engineer documents did not match the design documents. Incompetence number one. The machinist would have seen with the naked eye very easily that the hole was not close to center, an old salt would have raised it up. Incompetence number 2. The machinist not being aware that moving the jig was ruining the setpoint. Incompetence number 3. There were clearly incompetent individuals working at the facility. I get what you are saying... Don't blame the individual but best thing you can do from a process perspective is hire good people.
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I know very basic machining, but I know that part looks almost so simple I could manufacture it.
It’s very interesting that there were not wall thickness measurements. That would have solved this whole issue.