RE: Bolt-nut-combinations with cotter pins conrad1 (Aerospace)Ĭonrad1 made an initial statement that I’m extremely confused and uncomfortable about, thus. Unfortunately, in some cases there is no suitable alternative currently available. So using a castellated locknut with lower material strength than the shear bolt should not pose a problem.Īs a general rule, the use of cotter pins and lock wire is discouraged in the aerospace industry due to the FOD hazard it presents. If the nut is not axially preloaded at installation, it probably is not intended for any significant axial loading. The type of joint this fastener combination is normally used for would not be axially preloaded and some amount of axial clearance would be acceptable, so the nut slots can readily be aligned with the pre-drilled hole in the bolt. The MS17825 nut noted only has slots spaced 60 degrees apart, which means the max angular tolerance range of the installed nut is +/- 30deg. With threaded fasteners that are axially preloaded at installation, the two separate locking functions are provided by (1) friction at the thread flank contacts from axial preload, and (2) prevailing torque friction in the threads created by the interference fit of the locking feature.Īs you're probably aware, the combination of a pre-drilled bolt & castellated locknut does not allow precision indexing of the installed nut. If you take a look at FAR 25.607, you'll note this requirement, "(a) Each removable bolt, screw, nut, pin, or other removable fastener must incorporate two separate locking devices.". The combination of a castellated locknut and cotter pin is normally only used with a shear bolt that must be free to rotate (like a clevis joint). I'm assuming this is an aircraft application. RE: Bolt-nut-combinations with cotter pins verymadmac (Mechanical) 1 Sep 17 06:58 I think this is not a proper bolt-nut combination, although it´s an appropriate combination regarding strengths and resistances.Ĭan anyone help or recommend a better combination? This bolt-nut combination would require a lot of different thick washers. For a 5/16 UNJF thread, the distance between the slot ground of the nut and the beginning of the pin hole is only about 0,152mm (0,006”). The distance between the beginning of the close tolerance diameter (without thread) and the cotter pin hole is nearly the same distance as the nut height. The combination between the MS9358 nut and the NAS670x bolt is good regarding very similar strengths and resistances, but not regarding mounting and locking them with cotter pins. The MS9358 or AS9358 nut seems to be a better one, not least because it´s made of the same material as the bolt. The tensile strength of the MS nut is approximately only half of the NAS bolt. During the stress calculations of the bolted connections, a problem raised by the low tensile strength of the MS nuts. I usually choose the combination NAS670x (bolt) and MS17825 (nut) – and the cotter pin of course.
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