Don Bruder wrote:

Perhaps all of these are true. Perhaps none of them are. That isn't
important. What is important is that he got it done, and, regardless of
how or why, he got it done without getting hemself damaged or dead in
the process.

In my opinion, what is important is that people realize the fact that
he got away with it doesn't in and of itself make it a good idea, or
safe. Without getting into the specifics of the valve removal this
can be discussed as a matter of philosophy. i.e. doing something
risky and getting away with it for a while doesn't make it either safe
or a good idea. Its good to be lucky, but it isn't a good idea to
depend on it over the long term.

They flew the shuttles with burnt O-rings that were not supposed to
burn for quite a long time before they lost the Challenger. They flew
with 11 times the foam falling off, when none at all was supposed to
fall off, after they changed the adhesive that they used to have for
several years before they lost the Columbia. In both cases the logic
was that because it worked a few times it was safe. History has
shown, with tragic outcomes, the flaw in that logic, though it seems
to be a lesson that is very hard to learn.

The deal is that a contemplated course of action should be shown to be
safe, or have acceptable risk vs payback, or one doesn't proceed. One
does not have to show something to be unsafe to avoid proceeding. The
difference is profound.

Doing risky things and getting away with it is a matter of chance. Do
it once, you have a better chance of dying from other causes than if
you do that same risky act a lot. People pass over the yellow line
and may get away with it. People cut in and out of traffic on
freeways at high speeds and get away with it. People who do these
things a lot usually don't. There are similarities.

Shop safety is much the same. I file on the lathe by holding my right
arm over the work with the file handle in my left hand to avoid having
my arm over the chuck. Most folks I know do it the other way. I
suspect this is probably because they are right handed and want the
file handle in their right hand. I'm right handed, but with practice
it doesn't matter. The chuck, in my experience, is more likely to be
able to grab the arm or clothes because:

a) its bigger in diameter and closer to the arm than most of the work
on the lathe

b) it can have grabby things sticking up like chuck jaw ends that are
usually not there on the work. They can be, in which case maybe the
chuck end is safer in that instance, but usually the work where the
right arm is smooth.

Similarly, when using a lathe dog between centers, I don't want my arm
over it, even if it is the "safety" type with a recessed setscrew.
People file with their arm over the chuck a lot, but I don't think it
is as safe as doing it the other way.

Its called risk management. Its a personal choice.

You pick your pony, you take your ride.

Fitch