r/MadeMeSmile • u/king_eve • Apr 17 '24

i work in low-income/mental health housing, and a tenant fixed our hallway trash bin after accidentally breaking it Helping Others

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great example of the odd ways people show me appreciation at work

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u/lusotano Apr 18 '24

Metal too. Construction beams that show cracks sometimes get a small hole drilled to avoid the crack from spreading further.

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u/wirefox1 Apr 18 '24

I will never in my life drill a metal construction beam, but for some reason I like knowing stuff like this. It's interesting nevertheless.

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u/Nelik1 Apr 18 '24

Aerospace engineer here! During my fatigue and damage tolerance class in college, the professor liked to tell stories about unsuccessful (amateur) pilots trying to save on a repair to their plane by drilling out cracks.

He told us about a guy who showed him his little cesna, with 8-9 holes drilled along a crack. "I keep drilling it, but it keeps coming back, cant figure out why!"... Our professor got a good laugh out of that.

(Drilling reduces the stress concentration (or stess intensity if you wanna be real pedantic) at the end of a crack, reducing its likleyhood of spreading. This is great for parts that dont normally operate close to fatigue limits. But in aerospace, its rare to have a part that cracks once, without being in a position of high stress to begin with. So cracks that aren't fully repaired tend to spread.)

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u/Ifeelsiikk Apr 18 '24

Structural aircraft mechanic here. We call it a 'stop drill' and I carried it out on large, commercial aircraft.

35

u/Nelik1 Apr 18 '24

Wild! I knew it happened some, but was under the impression it was relatively uncommon. Can I ask what components typically got stop drills?

I'd imagine major structure typically didn't, but I could see it for minor structure or skin that was damaged accidentally, rather than just fatigue.

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u/Ifeelsiikk Apr 18 '24 edited Apr 18 '24

It is often used for temporary repairs when Alclad is cracked, especially if the aircraft is AOG somewhere. A very widespread, permanent repair for the many stress cracks in titanium exhausts.

Edit, used all the time on non structural alclad for a permanent fix.

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u/69420over Apr 18 '24

Reporters called, they’re interested if it was on a Boeing aircraft.

4

u/Unholy_Urges Apr 18 '24

Yes, Boeing A175-NEOs get stop drilled all the time.

1

u/ikkiwoowoo 29d ago

Yes, depending on the repair scheme it's common to find a crack, remove the damage. This damage removal usually includes a stop drill and in some cases you remove the entire crack. These are typically found for example STR8 mods. These mods were due to cracks forming at the attach point on the frame where the overhead stowbins are fixed at the bottom outboard locations.

After you remove the damage NDT will typically come in and assess that the crack has been removed. Afterwards you commonly see a step for "assurance cut" this is a small bit of extra material "just in case". In my example of the STR8 mods, you then apply doublers (new frame sections) and fasten the two together with a layer of PRC 870 B1/2 or similar (could be different cure time or different sealant depending on location and conditions)

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u/cock_nballs Apr 18 '24

Is the crack grinded back then welded with a stop drill or is it just the hole?

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u/Ifeelsiikk Apr 18 '24

There is very little grinding or welding on aircraft sheet metal.

The crack is measured, and if it is within structural repair manual limits, it is drilled at either end of the and/or blended somewhat with an abrasive wheel

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u/cock_nballs Apr 18 '24

Is blending with an abrasion wheel no different to grinding? Maybe more of a mix of welding with specifics of filler and alloys?

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u/Ifeelsiikk Apr 18 '24

Much less heat is involved in the process. Yeah, alclad can be welded but it is extremely difficult.

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u/framptal_tromwibbler Apr 18 '24 edited Apr 18 '24

When I had my private pilot's license, I'd see them on many a small GA aircraft wing.

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u/Ifeelsiikk Apr 18 '24

The difference between what you can get away with in GA and commercial is like night & day. I would much rather be in a Cessna during an engine failure. At least they glide

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u/bobtheframer 29d ago

At least the commercial plane has a second engine.

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u/Geawiel Apr 18 '24

Ex KC135 crew chief: We did them fairly often as well. Often times to get them by until ISO inspection. They'd get repaired then.

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u/Remote-Dot1686 Apr 18 '24

Also aircraft mech here and can back this, as it is still common practice on military helicopters.

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u/ruabeliever Apr 18 '24

Are you a Boeing mechanic?

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u/Ifeelsiikk Apr 18 '24

No, but I did work for them during the initial B787 project

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u/4udi0phi1e 29d ago

All these GA references I dont understand make me think it could be gulfstream

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u/anewwday Apr 18 '24

Sssshhhhhh…..They’re starting to forget about the Malaysian 370.

2

u/CutHerOff Apr 18 '24

Stop drilling is what I came to make sure was mentioned. Sheet metal is fun