GNH.Wbst207V@xerox.com wrote:
>
> to ridiculously low levels!) All the fittings were barely more than finger
>tight,
> because my friend (a very bright but non-technical salesman) did not *know*
> how tight to make them and feared breaking fittings off.
**** That's OK. Better than the guys who just twist the damn nuts off.
>From ``Zen and the Art of Motorcycle Maintenance'' by Robert Pirsig:
``..... There's what's called ``mechanic's feel,'' which is very obvious to
those who know what it is, but hard to describe to those who don't; and when
you see someone working on a machine who doesn't have it, you tend to suffer
with the machine.
The mechanic's feel comes from a deep inner kinesthetic feeling for the
elasticity of materials. Some materials, like ceramics have very little, so
that when you thread a porcelain fitting you're very careful not to apply
great pressures. Other materials, like steel, have tremendous elasticity,
more than rubber, but in a range in which, unless you're working with large
mechanical forces, the elasticity isn't apparent.
With nuts and bolts you're in the range of large mechanical forces and
you should understand that within these ranges metals are elastic. When you
take up a nut there's a point called ``finger-tight'' where there's contact
but no takeup of elasticity. Then there's ``snug', in which the easy surface
elasticity is taken up. Then there's a range called ``tight,'' in which all
the elasticity is taken up. The force required to reach these three points
is different for each size of nut and bolt, and different for lubricated
bolts and for locknuts. The forces are different for steel and cast iron
and brass and aluminum and plastics and ceramics. But a person with
mechanic's feel knows when something's tight and stops. A person without it
goes right on past and strips the threads or breaks the assembly.''
- Jerry
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