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Shanking fasteners

Shanking fasteners

Shanking fasteners

(OP)
What does this term mean?  as in "Shanking of fasteners is not allowed."

Thanks

RE: Shanking fasteners

To have the incorrect grip length of fastener where the nut "bottoms out" to the bolt shank. Correct grip length and use of hardware (washers) prevent shanking of fasteners.

RE: Shanking fasteners

luckyduc...

I think that Fieldteam’s explanation was for “thread-bottoming” or “nut-bottoming”… however thread-bottoming can lead to fastener-shanking (as described below).

Fastener Shanking.

Parts that fit poorly together, or are not clamped tightly together during assembly-fit-up, develop gaps at the mating-surfaces [faying surfaces]. Installing fasteners thru this stack-up [joint] results in exposed fastener shanks in each of the gaps. This is called "fastener shanking".  Note: For driven-rivets this situation is made even worse, since the rivet-shank will swell-excessively [mushroom] in each of these gaps, resulting in a localized hydraulic-pressure force trying to separate the parts even more.

The remedy to avoid shanking fasteners is "simple": shim [metal or resin] all ill-fitting rigid parts... or "pull-down" thin sheet metal parts to full/tight contact during pre-fastening assembly.

Why is this so important to eliminate gaps [in-a-nutshell]?

The gaps allow localized-flexure during cyclic loading, which can cause pre-mature cracking or fretting of the hole or fastener. Also, these gaps are great moisture traps [CORROSION] and are almost impossible to seal for fluid-tightness, since sealant will fill these areas initially... but eventually break-down [crack disintegrate, disbond, etc] due to excessive flexure [LEAKS].

Also, In "significant gapping" situations, small-diameter fasteners [especially soft rivets] will see added pin-bending forces that may result in failures well-below design-load capacity (distortion/cracking, etc). These joints are highly likely to fail the fastener-shanks exposed in gaps due to fatigue, fretting, corrosion or over-load…. although heads/tails could pull-off”, too.

Regards, Wil Taylor

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