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With the design of the knob exposed by this mishap, the cause of
the problem becomes evident.
The knob is molded around a knurled part of the bolt, and as the
yoke setup comes the knob bears on a plastic washer between it and
the outer yoke.
The shaft itself has a small flange more or less flush with the face of
the knob that I guess is intended to take some load in a similar fashion
to a bolt head, but the problem is that the plastic washer's hole is large
enough to let the diameter of that little flange squish right through.
So all the axial bearing stress ends up on the plastic knob face, basically
trying to push it outward off the knurled shaft.
Too much force, and something's gotta give.
To its credit, the bond between plastic and metal at the knurled section
is deceptively strong, if it could survive even a little bit of this.
In a conversation with Blizzard techs, though, it's clear that the usage as
supplied puts it at maximal disadvantage -- they've gotten a number
of similar reports of broken knobs.
A related characteristic is that since the plastic washers are a
friction element, any clockwise motion of the yoke relative to the
fixture will drag the knob along with it and effectively wrench this
assembly down really hard.
It's far too easy to do that with the Rokbox, even if you're careful.
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