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Figure 5 - bottom since the threads do not carry the load. proper application of the two-nut method is
The two nuts jammed together An advantage of a thin nut in this application is time intensive and requires a degree of skill
that a greater amount of axial backlash will be and is hence unlikely to make a major
provided for a given tolerance class. comeback on new machinery any time soon.
A series of tests were conducted to
investigate the effectiveness of the two-nut Figure 6 -
method in terms of resistance to self-
Results of a Junker Transverse Vibration Test
loosening. A Junker transverse vibration test
machine was used with M10 nuts and bolts.
The results are illustrated in figure 6. With the
small nut on top, both nuts can be observed to
rotate together and can subsequently come
completely loose. The results are slightly better
than is normally observed with a single plain
nut. With the small nut next to the joint, some
relaxation occurs but not a significant amount
of self-loosening. The performance of the
two-nut method, when properly applied,
provides a superior locking capability when
compared to many so-called lock nuts. The
Bill Eccles is a Chartered Engineer and formed his company Bolt Science some 16
years ago to specialise in bolting technology. The company writes and markets
bolted joint analysis software together with completing consultancy assignments
and training courses.
Further information is available from Bill via email (bill.eccles@boltscience.com)
or from the website www.boltscience.com
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