Kathy,
In our Space business we have a lot of hardware that requires torque during
assembly.  As others have responded, we too have a tool calibration
requirement but we also have a second-operator-verification (SOV)
requirement.  The design torque values are specified with roughly 10%
tolerance to allow use of most commonly available toque tools.  The operator
doing the torquing first obtains the appropriate tool that fits within the
90-10 rule (torque desired is within 90% of tool upper limit and greater
than 10% of full scale)and of the same scale as the spec. if possible. The
second operator verifies correct tool, setting and witnesses the torquing
event, signing off the assembly traveler.  Granted, in our relatively
low-volume assembly process this is the most reliable path.  High-volume
processes would have to rely on verification of process capability and
periodic audit where one-on-one verification is not practical.  Going back
and checking the torque again is not recommended because there will always
be a small amount of relaxation over time, especially with compliant
materials.  If you go back with the same torque wrench and see fastener
movement you would erroneously think it had not been properly torqued the
first time unless the time elapsed is very short, in the realm of minutes.
Back-off torque values are very low and really tell you little.  Torque it
accurately and verify it the first time and leave it.  After-the-fact torque
verification by inspectors sometimes include a visual inspection of washers,
that they have no gap under them or are loose.  This condition is possible
if the fastener bottomed out before clamping the parts.

> Rainer G. Blomberg
> Honeywell -Space Systems Clearwater
> Staff Production Engineer
(727) 539-5534



-----Original Message-----
From: Kathy Kuhlow [mailto:[log in to unmask]]
Sent: Thursday, September 05, 2002 1:03 PM
To: [log in to unmask]
Subject: [TN] Torque Inspections


I was curious how are torque requirements for hardware are being confirmed?
If a particular piece of hardware has a torque requirement of 12in/lbs how
would the verification of that piece of hardware be done?  Do you use a
torque driver at the same in/lbs or back off of the torque range or look for
loose(gap only)?

TIA
Kat

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