DIYbanter - View Single Post - Torque required to break screws

wrote:
OldScrawn wrote:
However I would have thought that at least some of the better
screw manufacturers would publish such figures.

Well, for "high tensile" bolts you can usually work out the values
from the numbers stamped on the heads. But then, you might want to
know the strength of the bolts if (say) you were using six of them
to hold a 2 inch flange on a 100 psi system. But you are not usually
doing stress analysis on wooden structures held together with
screws. Why were you asking? Find a friendly metallurgy lab and you
might get them to measure the hardness for a particular type of
screw, then there are formulae. Usually what you want in carpentry
is a joint that is as strong in shear as the wood. You don't need
much area of the weakest steel to get enough normal force across the
joint; friction and/or glue do the rest.

As I was trying to explain in my original question I'm not in the
slightest bit interested (well, not for this question anyway) what the
*tensile* strength of screws is. So it's not about how well they hold
things together.

What I'm after is how easy it is to break them, especially with a
power screwdriver.

BUT WHY????? If it is so you don't break any during 'installation' turn your
torque ring down so the screw is proud and then increase it till it's flush!
Nobody on here seems to know the answer to a question that seems
irrelevant!!

John