NAS1351 Heads Strip Below Installation Torque

[JCorsico]

thread2-442113

Resurrecting this old thread, I have a batch of NAS1351-3 (#10-32) socket head cap screws that are drilled for lock wire. The heads strip at a torque value that is below the desired installation torque value. Specifically, they strip at about 65-70 in-lbs (we were attempting to torque to 75 in-lbs). For reference, the Unbrako recommended installation torque for #10-32 socket head cap screws (190,000 psi tensile) is 91 in-lbs. An NAS1351 bolt should have comparable strength.

This is not an issue with the installation tooling, as we've carefully measured the hex bits and they all have acceptable dimensions (many bits are even 0.0005" or so oversize). It seems to be a problem with the fastener.

I then looked at the SPS catalog that Will previously provided in the above thread, and it includes a section where drilled head bolts from a competitor stripped easily. SPS's theory was that the defective bolts were annealed to allow drilling the lock wire holes, and then the heads were not re-heat treated.

I suspect that is the problem with my batch of bolts. Thanks Will!

Jon

 

[WKTaylor]

JC... one possible approach: drill [1] lock-wire hole thru the head [2-holes], ONLY... see IF You can live with just [1] thru-hole [pair].

Regards, Wil Taylor
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