Screwdriver length torque

[Nopax,thanx]

Right, here's one for the experts.....my lil sis visited this evening, she had a temperature logger which needed the battery changing and although she had got four of the six screws out, the remaining two had mashed. They were not very high quality self tappers, obviously driven into the plastic case with an air tool on the production line in Romania.

Anyway, she sought the assistance of her big bro (me) to get the recalcitrant fasteners out somehow. So, after trying various combinations of Pozi #1, #2, a little screwdriver, then a big one, I finally picked out a #2 phillips driver with a 30cm long metal shaft that I bought off the local market for 3 quid about 20 years ago. Now this little puppy has always been very good for torque, and sure enough, it gave the extra purchase to crack the screws and get them out, despite the wrecked heads.

So, here's the thing....how does a long driver like this give the extra bite that a shorter one does not? This particular tool has always had that bit extra when it comes to a bit of clout, even though it's quite slender and certainly no Snap-On or Proto weapon. One would think that torque would be a direct function of radius from the centre of drive, but in this case it is the distance from the point in a straight line that makes all the difference.

Your thoughts.....?

[knot4u]

I suspect it probably has a higher quality tip than you assume and your arm position is stronger when using it.

[ampclamp]

If both driver shafts were perfectly perpendicular to the screw and the torque applied was the same, given handle diameter etc, length should have no bearing. If however the longer driver was held off centre ( giving an apparent longer moment arm/ bigger radius ) you may get more torque on it. Just my thoughts.Not sure of this.

[Saint Jack]

Many, many years ago, one of my engineering mentors told me the 'trick' of using a longer screwdriver to loosen a tight screw when a standard length screwdriver wouldn't budge it. It has (almost) always worked for me. I don't know why it works - but it does work. No, it's not because the handle of the longer screwdriver may be fatter/wider producing more torque. Many 'old-timers' will know this and say the same.

[mad_jock]

I was told by an auld boy its all to do with the tip and handle.

He had two tool boxes one for day to day work and one for specials.

The special box contained all sorts of things some of which were quite scary and others as common as rocking horse poo.

He also had a old decommissioned SLR rifle piston which to this day I have never seen a better long drift. You can't hold of them though even when your in the services. Gawd knows what metal its made out of you trash a grinding wheel putting flats on the piston head to decommision it.

Some of his screw drivers were almost chisels and others more of an easy out drill. And he had re-tempered them all himself after adjusting them and quite a few were completely home made for specials. The handles as well weren't your normal type. Quite a few of them had lumps coming out the side which fitted along your palm and gave you lots of surface to push down on and also your palm provided the twisting moment instead of friction on the handle.

He was never defeated. And I never saw him break anything either it was usually a grunt and it was out. But his hand tight quite often defeated the rest of us.

[jxk]

Looking at this in the opposite direction: think of how awkward a 'stubby' screwdriver feels when needed and how you wish you could fiddle a full length screwdriver into position.
There is product on the market which looks and feels like grinding paste that can be quite useful for removing stubborn and damaged screws, you just put a little into the slot and it seems to grip the screw better. I think it's called 'Screw-Doctor'!

[stevef]

The added length gives a better angle for the wrist to apply more torque, coupled with using two hands to grip the screwdriver. Maybe...:confused:

[mad_jock]

Thinking about it.

Defection away from the vertcal would produce less angle at the head. So you wouldn't need to be cock on over the top to get symetrical pressure so more metal incontact at the same pressure?

Also as well the shaft will act as a torque dampener making it less likely that you will strip it?

Sounds like a good final year project to be honest for an engineering grad or MSC.

[helicopter pat]

A mate of mine has a golf club shaft with the end formed to take 1/4" bits.If that does not work then it is old with the drill & ezi-out.

[PowerDragTrim]

I was once told that a longer shaft meant that one could 'lean' over it more and therefore get extra weight to the tip and so avoid cam-out. This gave the impression of extra torque. Assuming all else equal i.e. one/two hands, etc.

[grounded27]

I would guess that it has a fine tip. Logically a longer screwdriver would provide better visual reference to maintain a closer to ideal 90deg angle to the surface the screw is in allowing for more surface contact inside the screw.

[mostlylurking]

My theory is 2 fold:
1. As mentioned, better alignment.
2. The longer & slimmer the screwdriver the more torsional energy it stores.
So you are able to build up torque more gently. In addition when the screw does let go, 'stick / slip' comes into play allowing the screw to loosen more in the first movement. There is a much more noticeable 'crack' as it lets go.

[Golden Rivet]

valve grinding paste is the answer to all stubborn fasteners...

[Capot]

The added length gives a better angle for the wrist to apply more torque, coupled with using two hands to grip the screwdriver. Maybe

I'll go with that, plus....longer screwdriver, wider handle = more torque from same force at wrist.

[Nopax,thanx]

Well, thanks for all the replies, I've found it most interesting. So, I reckon it's a combination of effects, the wrist position is certainly good, and I can feel the metal shaft twisting ever so slightly when undoing a tight fastener, which I think imparts a bit of extra torque.

It's a German driver, so pretty good quality, but I only ever bought it for the reach (it just fitted in through all the pipery around the hydraulic filter in a C-130 freight bay) never realising quite how good it would be in shifting stubborn screws.

So, if you don't have one, it's worth seeking out a nice, thin, long bladed driver; it will complement all of the others in your kit. Plus, my male pride is still intact, having got my sister out of a pickle!

[grounded27]

The ultimate resolution is a drill bit and an easy out! I have found a cordless motor and all my weight often very effective.

[jxk]

There is product on the market which looks and feels like grinding paste that can be quite useful for removing stubborn and damaged screws, you just put a little into the slot and it seems to grip the screw better. I think it's called 'Screw-Doctor'! It's not 'Screw-Doctor' but EzGrip and is marketed as an aviation product.
See: EzGrip :: screw extraction, friction drops, screw removal (http://www.ezgrip.net/)

[TZ350]

Hazet used to manufacture screwdrivers on which the blade thickness was parallel, as opposed to the tapered blade design that is usual. That, plus an excellent grip design, made them a pleasure to use and never damaged screw heads.

I believe the design is known as a gunsmiths screwdriver ? Unfortunately they do not seem to be available anymore in the Hazet catalogue.

[onetrack]

An impact driver is one of the finest items of equipment to have on hand when screws become recalcitrant.
However, they're more suited to items that are large enough to withstand impact.
I'm not sure how much impact a temperature logger would withstand.
One always has to determine the type of screw head correctly as well, before attacking it.
What with five common and two uncommon sizes of Philips, plus Pozidriv, plus Frearson, plus a couple of other "ring-ins" in the oddball driver dept, things can deteriorate rapidly, if the wrong driver is selected for the particular screw.

[Capot]

screwdrivers on which the blade thickness was parallel,

Also achievable, pretty much, with a grinder and an old screwdriver.

Not only does it grip better, but it can be used, with a Mk 1 Hammer, to improve the slot depth if needed.

[mad_jock]

An impact driver is one of the finest items of equipment to have on hand when screws become recalcitrant.

An avionics engineer with an impact driver :eek: