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Driving screws ...

Discussion in 'Electronic Repair' started by Arfa Daily, Aug 6, 2007.

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  1. Arfa Daily

    Arfa Daily Guest

    Totally off topic, but just for a bit of intellectual amusement ...

    Why should the length of a screwdriver's shaft, affect the amount of torque
    able to be given easily to the screw head ? This is something I learnt many
    years ago as an apprentice. I have just fitted a new 'antique' bog roll
    holder to one of my toilet rooms. The screws that came with it were nice
    single slot chrome plated jobs to match, but were about 2" long. When I came
    to drive them into the plastic wall plugs, I didn't want to use a power
    driver for fear of slipping out of that slot, so I went by hand. By the time
    I had got to 1.5" I was really struggling to keep the screw turning. Then I
    remembered the long screwdriver trick. I have one about 18" long. The shaft
    and tip and handle diameter were all near enough the same as the short
    screwdriver I had just been using. Only now, the screws drive in like you're
    putting them into a slab of butter. How can this be ?

  2. Mike Paff

    Mike Paff Guest

    Interesting... Maybe the longer screwdriver lets you apply more
    of your arm strength by moving your hand farther away from the wall?

    With the shorter one, were you in a slightly more awkward position
    and trying to use just your wrist to turn it?
  3. Arfa Daily

    Arfa Daily Guest

    That's a good thought. Maybe. If anyone doesn't believe this, just try it

  4. Ken Weitzel

    Ken Weitzel Guest


    Don't have to try it, been there, done it. Didn't ever get the
    tee shirt though :)

    I'm old and stroke damaged, so can't explain my theory nearly as
    eloquently as I'd like to, but my idea goes something like this...

    When you turn the handle against the resistance of the screw, you're
    to a small degree "winding up" the shaft. Naturally the longer the
    shaft the more you're able to wind it up.

    When the screw resists, it's not linear, but rather full of intermittent
    and random heavy resistance spots and easy spots.

    When the long shaft encounters one of these don't wanna spots,
    the shaft winds up until it finally overcomes the resistance.

    Someone please explain it better for me :)

    Take care.

  5. Charles

    Charles Guest

    Have you considered the size of the hand-grip? Longer screwdrivers have
    larger handles and thus a torque multiplier.
  6. Arfa Daily

    Arfa Daily Guest

    I'm following that ok Ken, and it's another good thought. There used to be a
    little car over here called a Morris Minor, and it employed just what you're
    describing, for its front suspension. "Torsion bar suspension" it was
    called. A bar a couple of feet long ran alongside the chassis members on
    each side. One end was fixed ( but adjustable ) and the other end was
    connected to the lower suspension arm. The bar twisted as the suspension arm
    moved, and provided the springiness. I think that is what you are thinking
    of as being the mechanism at play here.

    I might try sticking the business end of the driver in a vise, and seeing if
    I can indeed introduce some twist into the shaft.


  7. Arfa Daily

    Arfa Daily Guest

    Yes indeed, but as I said in the original post, the handles of the two
    drivers were much alike, as was the shaft diameter and tip dimension. The
    long driver is just that really. A perfectly normal 'average' sized tool,
    but with a very long shaft. I originally got it many years ago when I had to
    work on some graphics terminals, where the metal cabinet was secured to the
    front bezel, by two screws located right in the top corners of the case. The
    screws were spring loaded, so had to be driven *very* straight to get them
    to locate without cross-threading. The only way to do this was with a
    screwdriver 18" long, which was enough for the handle to be outside the back
    of the case.

  8. Just as an aside I was watching a CSI the other night where they were
    dismantling something in the lab using a dumpy screwdriver. Which
    absolutely no one would use unless forced to by space. The answer was, I
    reckon, it made a better framed close up in widescreen...
  9. DaveC

    DaveC Guest

    Why should the length of a screwdriver's shaft, affect the amount of torque
    My theory goes like this:
    Short shaft, you are mostly using the wrist to turn the screw driver. Wrist
    muscles tire easily.

    Long shaft, you can use your arm and shoulder (which are capable of greater
    strength) to rotate the screwdriver via a "locked" wrist (and if not locked,
    the twisting motion is shared by the forearm and wrist). Much easier on the
    wrist alone, which isn't known for it's strength. Having a longer shaft means
    it's easier to use your weight to lean on the screwdriver, keeping it in the
    screws' slot. Much harder to do with a short one.

    So it's not the screwdriver, per se, but which of the body's muscles you can
    put into play that make one screwdriver "easier" than another.
  10. Arfa Daily

    Arfa Daily Guest

    That's an interesting one Dave, and it kinda backs up what I'm saying. Even
    though you would expect to get a good 'torque multiplier' effect from the
    fat handle that those dumpies usually have, in fact it is actually very hard
    to undo a tight screw, or get a decent tighten on one either. If I'm forced
    by space to use one of them, I often finish up with a pair of Mole grips
    locked on the shaft to get enough purchase.

  11. WalkingMan

    WalkingMan Guest

    There were a whole lot of cars over here that used torsion bar
    suspension--the Chrysler Corp. By the way one of my neighbors has a
    restored Morris Minor, never drives it though.
    My 64 Chrysler used the torsion bar idea for keeping the trunk up.
  12. Arfa Daily

    Arfa Daily Guest

    Hi Dave
    This is the sort of theory that I have been coming around to as well, as I
    couldn't see any science that would explain it in terms of the physics of
    the screwdriver itself. I mean, you wouldn't expect a rear wheel drive car
    with a long prop shaft, to develop more torque at the diff, than one with a
    short prop shaft, given a similar engine and gearbox, would you ?

    I actually tried to visualize which muscles I was using, and whether it was
    anything to do with a locked wrist, at the time, but it was hard to say,
    which is why I was interested to hear the opinions of others who must have
    come across the phenomenum. I am sure that you must be right, but it is
    still difficult to see how such a subtle shift in muscle usage, produces
    such a huge difference in the amount of effort that can be applied to the

    I suppose that it's a bit like the difference between a drummer, and a
    'good' drummer. You can see some thrashing away at their drums, and only
    producing an average sound, whilst others seem to be putting hardly any
    effort in at all, and producing a really 'big' sound. Down to the technique
    of using the right muscle groups to put the force into the drumsticks, I

  13. isw

    isw Guest

    If the long-shaft driver is perfectly in line with the screw, there is
    no advantage. However, with a long-shaft driver, it's pretty easy to let
    it lean to the side a bit, and when you do that, the amount "off to one
    side" it is, gives you additional leverage -- like a short handle on a
    socket wrench.

  14. N Cook

    N Cook Guest

    a call on sci-med ?
    Who would ever use dumpy screwdrivers unles restricted access.
    My dumpy ones have parallel flats that i've ground into the shaft to take
    adjustable spanner.
  15. Arfa Daily

    Arfa Daily Guest

    That's an interesting one. I'm gonna have to think on that a bit ...

  16. jakdedert

    jakdedert Guest

    Arfa Daily wrote:
    It also may be useful to note that the longer shaft gives one more
    options on how to hold the tool. Likely one holds the screwdriver in a
    different fashion when the screw is stubborn (or simply tight). I know
    that I vary my grip depending on the amount of force necessary to remove
    a given fastener. A stubby can only be held in a limited number of ways.

  17. Ken G.

    Ken G. Guest

    The longer screwdriver has a sharper more newlike tip that stays in the
    screw better . The long drivers dont get used near as much as the normal
    familiar size which will have a sligtly worn tip causing you to fight it
    harder to keep the driver in the screw .
  18. Bob F

    Bob F Guest

    It's not force into the drumsticks. It's "pulling" the sound out with the
    drumtick. As the stick hits, it is being pulled away from the head.

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