Removing a seized screw.

[brenellic2000]

... I was thinking more on the lines of higher torsion and wind-up being transmitted through its elasticity as in torsion bar suspension, not possible with a 'stubby' screwdriver or Allen key...

[fetteler]

Herald is indeed correct.
Also worth noting is that in the static state the torque at the screwdriver tip will be will be unchanged by any elasticity and will be equal to that applied to the handle. In the dynamic state (i.e. when the screw starts to move) the tourque at the tip may lessen but it will never be greater thatn the torque applied to the handle.
This is Physics.


Steve

[richrussell]

I'd have drilled it out and found another screw. Once the head's started to break up, I don't bother wasting any time trying to save what is after all, a damaged screw. No need to try to remove it in one piece if it's going in the bin.

[Happy Listener]

Well, the damaged screw extraction tool did the job! As I suppose one would expect! Surprised it's taken so long to get a set for the tool kit... Thanks again for all the tips. Now the cover is off, I have to decide if it's worth the effort to restore or if it's too far gone under the nicotine and rust and it's a donor machine. But that's another thread!

[Nickthedentist]

Originally Posted by brenellic2000

... and the longer the screwdriver shank, the greater the torque can be applied with the least effort!

Whilst agreeing with the other responses to your explanation, I do have to admit that I have more luck removing stubborn screws with long-handled screwdrivers compared with short ones.

In certain DIY situations, e.g. fixing a blind in a window recess, a longer handle will allow the screwdriver shaft to be better aligned with the screw's axis (for a given handle diameter), but I'm at a loss to explain why it also seems to hold true in other circumstances.

It may, of course, be something daft like the fact that my very long-handled screwdrivers see less use so may be in better condition.

Nick.

[Herald1360]

I think the answer is already there- a longer screwdriver can accept the handle being further off centre before the blade loses its grip on the screwhead. So when you apply the grunt, the effect of any involuntary sideways movement superimposed on your torque generating efforts is less problematic.

The basic statement that it's easier to remove a stubborn screw with a long screwdriver is perfectly valid, it was just the explanation with which I begged to differ.

Of course a screwdriver in good condition well matched to the screw is a big help, too!

[brenellic2000]

... and while I'm still on a winning streak, I can whole-heartedly recommend in preferance to an electric drill for extracing screws, a good old fashioned Carpenter's brace - perfect control and a breast piece to apply weight.

Just make sure it has the Jacob's type parallel jaw chuck and not the mostly pre-war aligator tapered-jaw type for the old tapered shank drill bits.

Progress demands if it's good and works, they'll stop making them... which they have!

Barry

[Herald1360]

The best screwdriver I have for stubborn screws is an old Yankee 131 which is about 2 feet long extended. You can lean on it and inch it down the spiral without removing hands to get the next bite.

[brenellic2000]

... we're back to the increased torque and effort at the tip through torsional strain, elasticity and stored energy, plus the increased 'power' from the inclined screw surface of the Yankee spiral. The longer the shaft the greater the torque and power can be transmitted as transmission shafts (and screws) have a different set of rules to bog standard foot-poundals in a simple 'torque' application we were all taught at skool. It has nothing to with the angle of attack or grip at the screw-head!... but we're off topic here! This is advanced Fizzicks!!

I find Yankee spiral-screwdrivers are far more likely to slip at the screw (and damage the surrounding area) through pumping and that it defies logic to apply forward thrust when unscrewing! Personally, I think they're best avoided! A carpenter's brace is infinitely superior, easier to use and control and a darn sight better than an electric screwdriver! Luddites Rool!!

TTFN

[emeritus]

I recently removed a very small siezed contersunk screw (about 8BA ) that was too small for my screw extractors and too recessed to cut a cross head slot, by making a screw extractor from the shank of a broken HSS drill, grinding the end to a point in the form of a tapered 4 sided pyramid. I drilled a pilot hole in the screw and then followed with two sucessively larger drills to form a stepped hole so that the edges of the pyramid of the drill would have more than one set of edges to engage. The extractor was firmly tapped in to engage the stepped hole in the screw and turned wth a small pair of mole-type grips.

[fetteler]

Snip:

Originally Posted by brenellic2000

... we're back to the increased torque and effort at the tip through torsional strain, elasticity and stored energy, plus the increased 'power' from the inclined screw surface of the Yankee spiral. The longer the shaft the greater the torque and power can be transmitted as transmission shafts (and screws) have a different set of rules to bog standard foot-poundals in a simple 'torque' application we were all taught at skool. It has nothing to with the angle of attack or grip at the screw-head!... but we're off topic here! This is advanced Fizzicks!!


TTFN

Good Grief!
Please mods - end this thread now and ease my pain....

Steve.

[Station X]

We'll keep it open. I for one would like to know how using a longer shaft increases torque. If I use a torque wrench to tighten a nut, will the resultant torque at the nut depend on whether the extension bar is long or short?

[glowinganode]

Of course it won't, I've never heard anything so ridiculous.
Rob.

[Station X]

Neither have I, but I'm always ready to learn something new.

If we had a new olympic sport of "Bar twisting" with competitors trying to twist a long bar in opposite directions, which competitor would benefit from the increased torque at one end of the bar?

[brenellic2000]

How do you think they manage to drill oil wells with shafts several hundred feet long and only a few inches diameter? Fizzicks, of course! Don't forget that Einstein had to tweak e=mc squared to make it work! Fizzicks!

TTFN

[Station X]

That's a slightly different case to that of a long screwdriver turning a screw, because there'll be friction twixt drill pipe and the surrounding rock to overcome.

I still want to know how the torque at one end of a screwdriver shaft can be greater than that at the other. Can you point me to a text book which explains this? I don't disbelieve you, but I question things I don't understand until I do understand them.

[reelguy]

Happy Listener,
Re message 12. Having removed the screw on the cabinet of the Teac X10R ,What is the condition of the deck itself?. Just curious.
Peter W.....Reelguy.

[glowinganode]

I am willing to accept that once the screw starts to move, and if it experiences stick-slip, and the shaft is elastic enough to store sufficient torsional energy, and the handle has sufficient inertia to react against there could be a marginal benefit.
However this marginal benefit is unlikely to exceed the torque required to "break" the thread in the first place, this torque generally being limited by the condition of the head of the fastener and the condition of the driver.
In fact any energy absorbed by the shaft of the driver will reduce the effectiveness of impact techniques.
I'm not wholly convinced.
Rob.

[kalee20]

I can't see that a longer shaft will increase static torque.

Consider someone trying to undo a screw with a very long-shanked screwdriver, having no luck, but persevering with a steady applied torque. The shank will twist slightly with applied torque, reaching equilibrium.

Along comes another person, of identical muscular physique, and clamps a wrap-around handle at the shaft mid-point. They then hold this handle rigidly at whatever position it happens to be.

The first person at the end, gets fed up and releases their grip. Immediately, the torque coming down the stressed shaft above the extra handle disappears, as the top part of the shank untwists, so the second person suddenly finds they have to apply torque to hold the shank mid-point at the same rotational position.

As the shank, from the mid-point to the stuck screw, stays exactly motionless, the screw doesn't 'know' anything has happened.

However, the top part of the shank, from the mid-point to the original handle, is now serving no purpose, so while the second person continues to hold in position, along comes somebody with a hacksaw and cuts it off.

We now have a situation where the same torque is applied, the shank is only half the length, and the screw doesn't see any difference.

In practical aspects, shaft wind-up will rather confuse the sensation at your hand, which is a minus. But, as pointed out, small lateral movements of your hand will result in a lesser angular misalignment of driver and screw.

[brenellic2000]

Station X - I never said you can get more torque at the tip than you can put in!

But Rob has applied the correct lateral thought in understanding the solution to the problem about transmission of the power/torque/stored energy to break the resistance and or tensile strain at the screw head or in the threaded shank. It is a lot easier with a long shank than short!

Also when transmitting power/turning-motion down screwdriver shaft an increased angle of attack to the head (by going slightly off centre) cannot increase torque: that can only come from applying a spanner to the shank, or via a universal joint, to allow extra leverage, but what that offset will do is damage the head and defeat the object of the exercise!

I hope your grey cells have enjoyed this teasing little conundrum.