Doesn't make sense
Regarding the above post Permlink #198)- “News reporting here in Oz that the problem has been traced to a manufacturing defect. Apparently the section rivets were incorrectly fitted - the drilled holes were too large, leading to movement in the joint.”
This doesn’t make sense. Here is why.
Rivets or Hy-Locs ?
If the fasteners were rivets – then the rivets would assume the precise size of the holes drilled as they swell. We are talking in a few thousands of an inch and assuming they didn’t abandon all common sense (if it wiggles, something is wrong).
More likely - they were Hy-Locs which come in graduated oversizes to accommodate hole sizes including those that have been re-worked or enlarged in the removal of any earlier fasteners (rivets or Hy-Locs). For each specific oversized Hy-Loc, there is a specific oversized drill. Hy-Locs come in two components; the Hy-Loc itself, and a threaded collar incorporating a hex/nut portion to allow the collar to be driven by a wrench, a socket, or more commonly, an air powered driven socket wrench. Once proper tension is achieved, the ‘nut’ portion snaps away and leaves a small collar.
Hy-Locs won’t install in an oversized hole.
More importantly, there is a built-in feature to prevent wrong sizing with every Hy-Loc installation. The ‘nut’ can only be driven if the Hy-Loc does not rotate in the hole.
You can not drive the nut to the required tension permitting the ‘nut’ portion to snap away with a spinning Hy-Loc !
It is this interference fit – the ‘grip’ – that assures the hole sizing, and the Hy-Loc size selected are proper.
Drilling out fasteners changes the original hole sizes
Lastly, you can’t determine the original hole size after having drilled out a rivet. When it was driven, it may have swelled and expanded that hole, or more likely, by drilling it out, some hole material was also taken out as well and thus you have a ‘double hole’, one that is enlarged or ‘out-of-round’.
So, in sum, wrong sized holes at the manufacturing level where thousands of fasteners are installed a day seems highly improbable where not only are the installers involved, but also the Q.C. guys. It doesn’t make sense. Boeing has had a number of controversies but the very basics of fastening shouldn’t be one of them.
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