I don't get that either. A screw is a helical ramp, more or less. You
turn it to go in and come out. The farther the screw is in, the more
friction/resistance there is in both directions. Most often, I find it
necessary to push on a screw when removing it, at least until it's a
good deal out.
What am I missing?
"Playing is not something I do at night, it's my function in life"
Well, I should clarify my remark, since there appears to be at least 2
1. The friction (between the bottom of the screw head, and the
workpiece) that I alluded to.
2. The fact that you are pushing "down" when you wish for the screw to
come "up", that has been mentioned.
Because the objective is to _raise_ the screw. Pusing down on it
makes that harder to do and thus requires more torque to raise it. To
get more torque without cam-out yout have to push harder, which then
requires more torque to raise the screw, which requires you to push
True. But the point is you're better off using a screw head and bit
design that minimizes the amount of pushing required -- especially
when removing a screw since the pushing is forcing the screw in the
Since the amount that you wish to raise the screw head with a twist of
the wrist is very, very, small, I think the
effect you describe may be negligible. Of course, the wider the
threads, the greater the effect. I could probably
design a screw that would be difficult to unscrew by pushing down on
it! ; )
On Friday, August 1, 2014 8:12:41 PM UTC-7, Ed Pawlowski wrote:
Yeah, there IS a screw head design that allows you to pull. The
screw has a dovetail slot, curved so the driver can be positioned
at one edge and rocked into the slot. This scheme is not
compatible with magnet-held hex shank bits.
On Fri, 01 Aug 2014 12:55:57 -0400, email@example.com wrote:
I guess there is a difference between the generic "square-drive" now
being sold in the USA and the original Canadian Robertson (or Scrulox)
screws and screwdrivers. I know I've seen a lot af really crappy
square drive screwdrivers recently, and a lot of REALLY crappy screws
of all types with Chinese lettering on the boxes.. And the difference
between pozi-drive, Reed and Prince (aka Freerson), and Philips screws
and drivers causes a LOT of problems because they look so similar but
are virtually incompatible.
On Fri, 01 Aug 2014 22:33:16 -0400, firstname.lastname@example.org wrote:
Anyone with a torque screw driver want to do a test? Drive several
identical screws into severel peices of different woods then read the
torque required to remove them with no downward force, and with , say,
5, 10, and 15 lbs of force pressing on the screw and tabulate the
results? In both hard wood and soft wood - and using both steel and
I'd be willing to bet the difference in torque required would be
within the limits of the torque required to lift the downward force
treating the screw as a simple inclined plane. (in other words,
I think the initial "breaking loose" of the screw to get it to turn requires
more down pressure and torque than does the following turns... I think back
to the days of working on motorcycles and using an impact driver that was
hit with a hammer to break Phillips head screws free as an extreme example.
A less extreme example is when I've hit the handle of the screw driver with
a hammer as I put rotational force upon it to break the screw free. More
typically I push down hard with the screw driver to break the screw free and
them use primarily rotational torque to remove them. When using a powered
driver (usually my PC drywall driver) with various bits the same dynamic
occurs... I need a lot more down pressure to break the screws loose than to
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