I see people recommending to heat to red hot then quench with water or thin
oils, and it makes me cringe a little bit. There are real chances that the
metallurgy of the nut or bolt is going to be significantly changed, and
brittle to the point that it snaps off.
If the goal is to break a nut off, and it is replaceable (not left handed or
something) go for it I guess. I myself would not want to heat up a part
that was going to be used again past straw temperature, which is barely
showing any dull orange at all. If breaking the nut was a reasonable
option, I would just use a mechanical nut buster and be done with it if
impact wrenches and granny helper bars did not do the trick.
By the way, has it been confirmed that the nut that will not come off is not
a left handed nut? If there are three blades, it is most likely that at
least one (the middle blade) is a left handed nut.
At this point, I would say it is irrelevant.
What is apparent is that a screw head thread has managed to usurp the
place of the infamous wRec electrical threads in the amount of bullshit
contained therein. ;)
lot less than when I just try to muscle them out without heat - and
heating and shocking is a LOT more effective than heating alone.
In critical applications you replace the bolt. Half the time it is so
badly corroded you'd be crazy to try to re-use it even in non-critical
For me the most important thing is the quality of the steel of the
screw. Buy screws where the metal has been heat treated to make them
tougher. The shape of the head recess comes next in my book. Then, I
put toilet bowl wax on the threads to make them drive much easier.
Someone made a point that you don't want to have to press very hard
when removing a screw. I find this isn't a bigt issue unless the screw
has stripped out the material it is attached to.
My wife was helping me put up a fence in our yard. I started her
driving screws with Robertson (square) heads. She had trouble holding
the drill steady enough to keep the bit aligned. She had no trouble
with the star shaped screw heads.
Probably if I had a hammer driver at the time it wouldn't have been a
problem. Now I do. It makes the OP's question less important.
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