All Torque?

[The Medway Handyman]

Just been watching Tommy Walsh on TV. He (and an elderly joiner) ascertained that a longer screwdriver enabled you to apply more torque.

I went on a Wolf Power Tools course many years ago (when God was a boy) and they claimed that the length of the drill was irrelevant, only the diameter mattered.

One of these claims must be false. Granted a longer drill must take more power to deal with material clearance through the flutes, but I can't see why a longer screwdriver applies more torque.

If this is the case, should we all be using extra length bit holders on cordless drills?

[George]

Try it next time you have a stubborn screw...you'll find a longer blade can shift it providing the slot hasn't been mangled. :-)

[dom]

It may be about the motion of the wrist and forearm. With a stubby screwdriver, the motion must remain exactly on axis. With a longer driver, a combination of axial twist whilst moving the hand in a small circle is possible - possibly meaning the wrist is more rigid and some of the action coming from movement at the shoulder and elbow. That may confer some mechanical advantage if the wrist can be held more rigidly in some positions more than others. Or it may not.

[Chas]

Fucken dimwit! Did you ever go to school or was you always just a cleaner?

[John Rumm]

I think they key may be in the application, rather than the transmission. The longer driver will probably let you hold the driver closer in to the body, allowing you to lock your arms against the body and use a whole body movement to apply torque, rather than doing it more at arms length which reduces your mechanical advantage.

A longer drill may encounter more friction, but only if used to drill a deeper hole than would be possible with a shorter one.

No, or at least certainly not with an impact driver. The less torsional flexibility in the linkages the better since they absorb some of the impact impulse energy.

[John Rumm]

More milk tibbles?

[Bob Mannix]

No, of course not! With a shorter screwdriver, off axis movements at the hand end, which are inevitable as you apply serious torque, convert very quickly into an unacceptable angle the blade makes with a screw. With old slot head screws, you would then get the blade slipping out of the slot and mangling the screw. With a long shafted screwdriver, the allowable movement at the hand end is greater so you can more easily apply greater torque without the danger of slippage. Therefore, even if indirectly, longer screwdriver = greater torque possible. For pozidrives in a power tool, this is, of course, irrelevant.

[Ian White]

If the longer screwdriver allows you to brace your arm/wrist against your rib-cage and get some body weight above the job, then you probably can apply more torque than you could with a short driver and extended arm. Or at least, you can apply more forward force to avoid cam-out.

Only if they're totally rigid.

[Dave Plowman (News)]

It's to do with how the human arm can apply torque to a screwdriver. Grip and so on. Doesn't apply with a power tool - unless you have problems holding it. ;-)

[TheScullster]

"The Medway Handyman" wrote

The key is in the small print as ever:

As has been stated by others, it is possible for a person to apply more torque to a longer driver (therefore Tommy is right). However, assuming the same materials and shaft dimensions are used, the maximum transmittable torque will be the same for a long or short driver (therefore your power tools course is also correct).

Phil

[Colin Wilson]

Steel has a natural "spring" to it - perhaps a longer shaft allows this springy nature to direct the applied force to the screw better ?

[dennis]

Not irrelevant.. it is easier to keep the head in line with a longer screwdriver even(especially?) in a drill. Pozidrives don't like the screwdriver to be out of line, they strip easily.

[Derek Geldard]

I think it's because you can use different ( IE bigger & stronger) muscles to drive a long screwdriver.

DG

[Roger]

The message from "The Medway Handyman" contains these words:

I don't buy the idea that a longer shaft alters the way in which the body can deliver torque. If the handle is the same size then ultimately the hand to shaft maximum torque will be the same. Where there does seem scope for the longer shafted drivers is in extra leverage by using the the screwdriver at a slight angle. Provided the end of the driver can still engage the screw it would have the same effect as using a screwdriver with a fatter handle.

[Bob Mannix]

Well it's always easier to keep a long driver in line, granted. My point was, with a power driver, it's actually quite easy to keep a short one in line, irrespective of the torque (which is where it differs from a hand tool).

Bob>

[Mungo "Two Sheds" Toadfoot]

Oh, the irony.

Si

[NoSpam]

There are 2 things going on. The longer shaft means that small movements in the hand position cause less movement at the tip so the driving end is less likely to cam out of the screw. Longer screwdrivers tend to have larger handles so the force is being applied further from the centre of the shaft.

Dave

[Brian G]

It's all in the 'twist' gents, it's all in the twist - and the fact that usually the longer the screwdriver, the bigger the handle - and as as we all know, a big handle allows a better grip :-)

At least that what I was told 48 years ago when I started my apprenticeship and at fifteen, who was I to doubt such wisdom - and the elders amongst us would understand what would have happened to me if I did..... ROLFLMAO

Brian G

[Andy Dingley]

Yes. Just try it with a big old ratchet screwdriver, like a Spiralux or a Stanley, that's a couple of feet long.

Of course the torque you can apply depends on the diameter of the screwdriver handle. However the torque you can _usefully_ apply is increased by using a long handled screwdriver with a separated two-handed grip.

If you try to gorillate things by applying a lot of torque to a short-handled screwdriver with a long blade, then the relative lever length between both hands, compared to the nearest-hand to blade distance means you're likely to slip with it. If you can get your hands separated (long handle), then you can apply much more torque in a controlled fashion. Similarly, a stubby (short blade) screwdriver can give much the same result, so long as you've still got space to get two hands onto it.