OK, so square (four sides) is better than slot (two sides), and
octagonal (eight sides) is even better than four sides, the logical
conclusion would seem to be than the more sides the better.
Take that to the limit as sides -> infinity, and you get what must
be the best of all: round drive (or as it is usually known: cheap
philips head screws after use with the wrong sized driver).
There's probably some truth in that... But remember the bit you used to
make the round isn't making a good quality round. It's kinda like those
Combo drive screws or the square drives that are almost, but not quite,
Make a good quality round, use a good quality round bit, and pull rather
than push and the screw will come out easily.
(Do be careful not to make the round too round. You might wind up cold
welding the bit to the screw. :-))
On Sat, 02 Aug 2014 12:14:44 -0400, email@example.com wrote:
Except, particularly in a woodscrew (and this IS a woodworking group)
the pressure applied against the threads of the screw by the
compression of the wood fibers is SO much more than the pressure you
are applying to hold the screwdriver in, that the pressure you are
applying is totally insignificant.
And in th case of a machine screw, the pressure applied to the surface
by the head due to the torque of the screw, and it's torsional stress,
again makes ANY pressure you are going to apply TOTALLY irrelevent.
The friction on the upper surface of the thread due to the installed
tension will be 10 or more times what the friction on the bottom of
the screw thread would be from the pressure you apply.
In FACT, hitting a screw on the head while turning it is a well known,
shop worn method of removing a stuck screw or bolt.
Again - I say "red herring"
On Sat, 02 Aug 2014 12:18:42 -0400, firstname.lastname@example.org wrote:
Not nearly as "beyond belief" as thinking the pressure you apply to
the head of a screw to keep the driver engaged is going to increase
the torque required to remove screws that have weathered a decade due
to increased friction in the threads!!!!
You really do not have a CLUE.
On Sat, 02 Aug 2014 18:35:05 -0400, email@example.com wrote:
Pardon? The friction provided by the wood gripping the screw is what
makes a screw difficult to remove. The friction between the wood and
the threads, plus the friction between the wood and the shank.. If
anything, putting pressure on the screw would DECREASE the friction on
the top of the threads while increasing the friction on the bottom -
either netting out or reducing the total friction on the screw - so
either keepi ng the required torque the same or less. Certainly no
great increase in required torque.
OK - I'm not a physics major - just a dumb mechanic. The tension load
placed on the screw by virtue of the torque applied to the fastener
puts very high pressure on the interface between the head of the
fastener and the surface of the material being bolted together. The
pressure can be in the hundreds of lbs. The break-away torque required
to overcome the stiction between the screw head and the bolted
material is often significantly more than the torque required to
continue turning the fastener after it is broken loose. The force
required to overcome the "static friction" in the threads - breaking
the bonds of rust and corrosion, is also quite substantial. So is the
"running friction" between a corroded fastener and the internal
threads of the material being fastened, or the nut. So substantial as
to render the incredibly small amount of extra friction caused by even
40 lbs of pressure applied to the screwdriver to keep the driver in
the head of the screw almost totally incosequential.
Again - you are not reading what was said very well for a PHD in
Physics (or someone who plays one on TV) Nowhere did I say the
friction on the threads is irrelevant. I said your contribution to the
friction on the threads is totally irrelevent. Your effect on the
universe is greatly overestimated.
Who said anything about "screw removers" by which I assume you are
referring to "impact drivers" which you hit with a hammer, causing a
cam to rotate the fastener. I'm talking about beating the bejeapers
out of the head of a bolt while pulling on a wrench to break free a
seized bolt. It is a VERY effective method of breaking loose large
threaded fasteners in old equipment.
Nope. I have removed thousands of stubborn fasteners from old
equipment over the last 50 years. Some of them litterally seized by
"bullshit" which can REALLY make things stick. Ever try removing bolts
from the apron chain of an old shit-spreader????
That device is not what is termed a "screw remover". I have to side with
clare on this one - I have such a device in my toolbox - albeit for metal
and not wood, but the principle is the same: you insert the tool into the
screw head, apply torque, then hit the end with a hammer. The tool has a
heavy spring inside and a spiral mechanism - when you hit it with a hammer,
it applies more torque than you can apply with your hands - plus vibration,
This sounds like an impact wrench. The impact of the hammer is
converted to torque. There is some advantage hammering to break
metal-metal binding (essentially a "weld") but you're applying torque
constantly. The impact only increases friction for the milliseconds
of the impact. Sorry, physics doesn't care about consensus.
On Sun, 03 Aug 2014 11:22:11 -0400, firstname.lastname@example.org wrote:
And stuck bolts don't care about theoretical physics. Have you ever
had to remove any REALLY stuck bolts?? Your physics theory won't
remove them. And I can guarantee you would not be able to measure the
amount of extra torque required to remove a stuck bolt due to the
extra friction (if any) caused by pushing on the screwdriver to hold
the bit in the head without extremely accurate lab measurement
equipment.(and a good dose of imagination)
I have a stuck bolt right now holding a lawnmower blade on that belongs
to my neighbor lady, removed two of the blades but the third one will
not budge. I have used an impact wrench but someone had rounded the bolt
before and even tapping a smaller fraction size on it will not grab good
enough. Tried vice grips and pipe wrench--what next, maybe heat. I am
afraid it will break and then the mower will be toast, it is an old John
Deere her husband had before passing away. Any ideas?
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