A large screw is no more likely to be in a deep hole than a small screw

MaximRecoil · Mar 11, 2011

So why does e.g. a #3 Phillips screwdriver usually have a longer shank than a #2 screwdriver; or why does a 5/16" blade screwdriver usually have a longer shank than a 1/4" blade screwdriver, and so on?

I know that there are exceptions, in that you can buy short large head screwdrivers, or long small head screwdrivers, but in general, like when you buy screwdrivers in a set, or choose from the standard selection on the hardware store wall, the length of the shank usually increases for every size that the head increases.

Bull · Mar 11, 2011

I think it's all about leverage, right? Larger screws require more force to remove, especially if stuck, and you get more leverage with a longer driver.

I am dismal with science and more of a reading and writing guy, so maybe I'm wrong. :headscrat

jjjrmx5 · Mar 11, 2011

MaximRecoil said:
So why does e.g. a #3 Phillips screwdriver usually have a longer shank than a #2 screwdriver; or why does a 5/16" blade screwdriver usually have a longer shank than a 1/4" blade screwdriver, and so on?

I know that there are exceptions, in that you can buy short large head screwdrivers, or long small head screwdrivers, but in general, like when you buy screwdrivers in a set, or choose from the standard selection on the hardware store wall, the length of the shank usually increases for every size that the head increases.

Lager screws (or any fastener really) often requires more torque to install and remove as you are trying move a larger mass thru an item with larger exposed surface area.

Larger fasteners can also be torqued tighter as the larger mass of the fastener will be less likely to shear or disfigure from overtorqueing.

So--not big enuff tool = reduced power. Too big a tool = great power but possibity of inducing failure in fastener shank or head. And for screwdrivers, encresed shaft length increases torque, so long as the grip is good enuff to allow it.

MaximRecoil · Mar 11, 2011

Bull said:
I think it's all about leverage, right? Larger screws require more force to remove, especially if stuck, and you get more leverage with a longer driver.

I am dismal with science and more of a reading and writing guy, so maybe I'm wrong.

Leverage doesn't come into play for the twisting that you do with a screwdriver, at least not in the form of shank length. The handle diameter is what gives you leverage for torque multiplication on a screwdriver. A larger diameter handle multiplies torque (due to leverage) the same as if you had a crank on the top of the shank and increased its length.

jjjrmx5 said:
Lager screws (or any fastener really) often requires more torque to install and remove as you are trying move a larger mass thru an item with larger exposed surface area.

Larger fasteners can also be torqued tighter as the larger mass of the fastener will be less likely to shear or disfigure from overtorqueing.

So--not big enuff tool = reduced power. Too big a tool = great power but possibity of inducing failure in fastener shank or head. And for screwdrivers, encresed shaft length increases torque, so long as the grip is good enuff to allow it.

A longer shank does not do anything to multiply torque in a screwdriver, as I mentioned above. You make the handle larger in diameter to accomplish that. It is like a drivetrain in a car. A longer driveshaft will not multiply torque; you can only multiply torque with the gearing in the transmission and/or the transfer case, and/or the differential(s), because that is where the leverage analogy (in the form of gear reduction) can come into play.

Bull · Mar 11, 2011

Dismal with science, I said! :lol_hitti

Now, where is a competent scientific/technical mind? Paging GJ engineers and physicists!

diesel research · Mar 11, 2011

This discussion had been beat up a few times. Mrholeshot said he could tighten a screw with a short shank and then use a long shank and get more turns. Likely what was happening was the longer shank was twisting more (so the handle moves while the tip stays put)

The idea of longer shank is identical to longer extension. Definitely doesn't help.

Perhaps the extra length is some kind of torque limiting function? Or more likely a marketing ploy since quite a few believe a longer screw driver=power, and would buy a longer one as opposed to a shorter one.

MaximRecoil · Mar 11, 2011

Bull said:
Dismal with science, I said!

Now, where is a competent scientific/technical mind? Paging GJ engineers and physicists!

Yeah, when it comes to mechanical advantages such as leverage, pulleys, gear reduction, there is always a trade-off, no free ride, i.e. you don't get the mechanical advantage for free.

For example, in the case of leverage, and using a pry bar as an example, less force is required to lift the object you are prying, but you have to move a greater distance; so the total work that you have to do is the same (a little more actually, due to inherent losses such as from friction). You might move the big rock you are prying on an inch, but have to move your end of the pry bar a foot.

The same applies to gear reduction. Your engine has to spin at higher RPMs to reach a given wheel speed. Pulleys that are arranged in a mechanical advantage pattern are the same way, i.e., you have to pull your rope a much greater distance than the load moves.

Keeping this in mind, you can test to see if a longer shank can possibly multiply torque on a screwdriver. Take two screwdrivers that have the same handle diameter, but different length shanks. Screw in or unscrew the same screw with both of them, and count the number of turns. You will find that the number of turns are the same regardless of the length of the shank (or more specifically, a given point on the outside of the handle will travel the same distance regardless of shank length), which means that it is impossible for a longer shank to provide any mechanical advantage, because if it did, that mechanical advantage would be free, and the universe would self-destruct or something (lol).

On the other hand, with a larger diameter handle (which does multiply torque on a screwdriver), the outside of the handle travels a greater distance to turn a screw a given distance compared to a smaller diameter handle, thus, you're paying for your ride.

MaximRecoil · Mar 11, 2011

diesel research said:
This discussion had been beat up a few times. Mrholeshot said he could tighten a screw with a short shank and then use a long shank and get more turns. Likely what was happening was the longer shank was twisting more (so the handle moves while the tip stays put)

Or the longer shank screwdriver had a larger diameter handle (and they do tend to have larger diameter handles), thus more torque multiplication.

Or more likely a marketing ploy since quite a few believe a longer screw driver=power, and would buy a longer one as opposed to a shorter one.

That could be.

OccupantRJ · Mar 11, 2011

The only way I have seen where a longer screwdriver can possibly allow more torque is that on a short screwdriver, you tend to use only hands to twist the handle. On a longer shank, you can sometimes push your chest into it, thereby keeping the tip in the screw recess. This is a matter of better control, rather than the shank length having an effect on the actual torque that the screwdriver can produce. You can produce more torque with your hands gripping a screwdriver against your chest than you can with the driver at arms length, because your upper body is assisting with the twisting action, not just your arms. Longer shank length will actually absorb some of the intended torque by twisting as force is applied.

diesel research · Mar 11, 2011

I've never used a screw driver like that. Maybe since I have wrench bolsters.

rsanter · Mar 11, 2011

its a matter of scale
you will more likly fins a #3 philips on a truck than a cell phone
so actually it is more likly to be in a 'deeper hole' or have other objects around it than a smaller screw

bob

OccupantRJ · Mar 11, 2011

diesel research said:
I've never used a screw driver like that. Maybe since I have wrench bolsters.

Next best thing to bolsters are square shanks! If I was just starting out again, I would also have bolsters on all my screwdrivers, but with several hundred around, I ain't starting fresh now!

trout · Mar 11, 2011

It's all a mental thing I think. Plus it makes it easier to identify.

MaximRecoil · Mar 11, 2011

rsanter said:
its a matter of scale
you will more likly fins a #3 philips on a truck than a cell phone
so actually it is more likly to be in a 'deeper hole' or have other objects around it than a smaller screw

bob

I don't recall ever seeing any large screws in deep holes, though small screws in deep holes are common in household devices that have a plastic shell (the original Nintendo for example, #1 Phillips). However, those holes aren't generally deep enough to require a particularly long shank; 4" is usually more than plenty.

Additionally, 3/8" blade screwdrivers are usually longer than 5/16" blade screwdrivers, even though both sizes of screws are far more likely to be found on a truck than a cell phone. The only 3/8" blade screwdriver I could find at the hardware store when I needed one had an 8" shank. I needed it for the screws in the **** of my AR-15, and the screws that hold the handles on my pots and pans. In neither case are the screws even remotely in a deep hole.

I don't think any standard screwdriver needs a shank longer than 4". That would save on cost and storage space, be maneuverable, and work for most applications. Save the extra long and extra short lengths for the specialty screwdrivers, as is normally done with other tools.

srmofo · Mar 11, 2011

OccupantRJ said:
Next best thing to bolsters are square shanks! If I was just starting out again, I would also have bolsters on all my screwdrivers, but with several hundred around, I ain't starting fresh now!

In my experience all the bolsters do is allow you to break stuff quicker :bounce:

. Ive shattered a few drivers that way and broken a few more screws also. With that said if it is stuck enough that you are breaking things, nothing is gonna get it out anyways.

Vicegrip · Mar 11, 2011

rsanter said:
its a matter of scale
you will more likly fins a #3 philips on a truck than a cell phone
so actually it is more likly to be in a 'deeper hole' or have other objects around it than a smaller screw

bob

I think the scale is what we have come to expect a standard screw driver to look like. Bigger shaft = longer driver. Ratio is dia to length. Normal proportions. Make the shaft shorter than the dia dictates and the purchaser will think it is more a stubby than a standard. I have a short flathead driver with a full size handle in the track tool box that tends to get borrowed from by a group. People comment on it.

MattT · Mar 11, 2011

The standard shank lengths are sized for prying. A 6" x 3/16" screwdriver would either bend or break if used as a prybar.

nikonica · Mar 11, 2011

I agree with Vicegrip - it's the scale that consumers have come to expect. We expect a Phillips #1 driver to be a 1/3-scale model of a Phillips #3 driver. This phenomenon is primarily evident in screwdriver sets, which in turn are mostly sold by the likes of Sears, Lowe's, and your local hardware store. If you look at a catalog of screwdrivers sold individually and marketed towards professional or industrial users, like Stanley 100 Plus, Snap-On, etc., you'll see that screwdrivers are available in many different tip size/shaft length combinations.

I prefer to use longer screwdrivers myself; my favorite Phillips #2 driver has a 10" shaft. It just feels better to me, for some reason, even when there is no need for the additional reach.

Stuey · Mar 11, 2011

The large the handle, the greater the torque that can be applied to a fastener if given the same user-applied turning force.

As for why the shafts must be longer for larger screwdriver sizes, I'll need to think about that for a bit.

Contrary to my instinctual belief that longer shafts do NOT lead to greater applied torques, I think that there definitely is a solid relationship there.

The idea that it's done for consumer convenience is good reasoning as well, but not really.

Stuey · Mar 11, 2011

Check out this thread:

http://answers.google.com/answers/threadview/id/24192.html

Some of the responses are similar to what I've been thinking. They discuss how the shafts of larger drivers are lengthened becuase the torsional spring behavior of the shaft can apply a little extra torque.

I'm also thinking that this is done to uniformly distribute the stored torsional energy in lesser incremental amounts. My thoughts are that larger drivers with smaller shafts could potentially lead to more damaged fasteners. If the fastener is resisting tightening, and the user keeps applying force, the shaft can only twist so much. A longer shaft will lower some of the energy from being transmitted to either the shaft, driving tip, or fastener head, helping to prevent failure of one or more of the system components.

mrholeshot · Mar 11, 2011

Not only can you get more of your body into the movement than a Stubby shaft where the handle would be close to the work surface but there is something to the length adding to the power of a screwdriver. May not make sence but been through it thousands of times.

MaximRecoil · Mar 11, 2011

Stuey said:
Check out this thread:

http://answers.google.com/answers/threadview/id/24192.html

Some of the responses are similar to what I've been thinking. They discuss how the shafts of larger drivers are lengthened becuase the torsional spring behavior of the shaft can apply a little extra torque.

I'm also thinking that this is done to uniformly distribute the stored torsional energy in lesser incremental amounts. My thoughts are that larger drivers with smaller shafts could potentially lead to more damaged fasteners. If the fastener is resisting tightening, and the user keeps applying force, the shaft can only twist so much. A longer shaft will lower some of the energy from being transmitted to either the shaft, driving tip, or fastener head, helping to prevent failure of one or more of the system components.

There was an interesting idea in that thread, i.e.:

"3.Improved ability to keep the screwdriver axis closely aligned with
the axis of the screw, thus ensuring the tip of the screwdriver
engages correctly with the slot and is less likely to slip out."

I'd never thought of that, but it is true. This is the same reason that longer barrels on guns with open sights tend to be more accurate. This is not because longer barrels have any inherent accuracy advantage (if anything, shorter barrels are more inherently accurate, all else being equal, because they are more rigid), but rather, the longer barrel allows for a larger sight radius, improving the precision in which one can align the sights, allowing the user to make better use of the available accuracy.

In the case of a screwdriver and typical shank lengths however, this effect is going to be very minor, probably even negligible, and I doubt any manufacturers have that in mind when deciding what length to make their shanks.

mrholeshot said:
but there is something to the length adding to the power of a screwdriver. May not make sence but been through it thousands of times.

Not only does it not make sense, but it is impossible for a longer shank to add power to the screwdriver. In fact, with a given input torque, the torque that reaches the screw will decrease as the length of the shank increases, all else being equal. This is because some of that torque will be lost in the shank itself, due to the torque required to move its mass in the first place (its mass increases as it gets longer) and the fact that with all else being equal, longer shafts have less torsional stiffness, resulting in greater losses through twisting. To take it to an extreme, imagine if the shank were lengthened to say, 100 yards. It would take most of your effort just to turn it, leaving little torque left over to turn the screw.

nw2571 · Mar 11, 2011

Stuey said:
Check out this thread:

http://answers.google.com/answers/threadview/id/24192.html

Some of the responses are similar to what I've been thinking. They discuss how the shafts of larger drivers are lengthened becuase the torsional spring behavior of the shaft can apply a little extra torque.

There is no "extra" torque being applied through the spring effect. Energy in the system must be conserved. To multiply torque using a spring would be in violation of several physical principles. Springs don't multiply force, they store energy.

The extra length makes the screwdriver less stiff, torsionally (assuming the same shaft cross-section). That is to say for a given amount of torque applied at one end there is more angular deflection over the length of the shaft. This would actually tend to slightly reduce the amount of torque transferred from one end of the driver to the other. Part of the applied torque is used to wind up the spring (shaft) which has some small losses.

This is mostly academic though. The torque limitations of a reasonably designed screwdriver aren't in the shaft anyway. The amount of torque you can apply is limited by either the stiffness of the tip, the screw itself, or the amount of torque a human can input to the screwdriver. The shaft is simply a way to connect the two ends of the screwdriver.

nw2571 · Mar 11, 2011

By the way, with a title like, "A large screw is no more likely to be in a deep hole than a small screw," I can't believe there hasn't been a single d*ck joke.

mrholeshot · Mar 11, 2011

MaximRecoil said:
Not only does it not make sense, but it is impossible for a longer shank to add power to the screwdriver.

You turn enough screws you figure out what works and what doesn't. Torsional energy, Like Prego it's in there :beer:

walrus · Mar 11, 2011

mrholeshot said:
You turn enough screws you figure out what works and what doesn't. Torsional energy, Like Prego it's in there

Why don't you explain how that myth works. You're saying if I use a screwdriver with a shaft of 20 ft I'll be able to loosen or tighten screws easier than a driver with a 4" shaft. Correct?

MaximRecoil · Mar 11, 2011

mrholeshot said:
You turn enough screws you figure out what works and what doesn't. Torsional energy, Like Prego it's in there

The energy returned to the screw from what you term as "torsional energy" can not exceed the energy that you put in in the first place. In fact, energy returned from a spring ("torsion bar" type spring in this case) will always be less than what was put in, due to inherent losses. If you have a screwdriver that can create energy then you would easily win the Nobel prize and shatter the foundations of physics as we know it.

walrus · Mar 11, 2011

MaximRecoil said:
The energy returned to the screw from what you term as "torsional energy" can not exceed the energy that you put in in the first place. In fact, energy returned from a spring ("torsion bar" type spring in this case) will always be less than what was put in, due to inherent losses. If you have a screwdriver that can create energy then you would easily win the Nobel prize and shatter the foundations of physics as we know it.

A few physics or Statics or Dynamics classes I see

diesel research · Mar 11, 2011

No, no. Not simple explanation, let's see some quality youtube'age.

(same size/style of handle required, along with shaft diameter)

MattT said:
The standard shank lengths are sized for prying. A 6" x 3/16" screwdriver would either bend or break if used as a prybar.

If you are suggesting a shorter shaft/board/bridge/prybar/frame rail/spring/nail/rod/pipe bends easier, your physics are backwards.

mrholeshot · Mar 11, 2011

walrus said:
Why don't you explain how that myth works. You're saying if I use a screwdriver with a shaft of 20 ft I'll be able to loosen or tighten screws easier than a driver with a 4" shaft. Correct?

Can't explain it. Send me a 20 foot screwdriver and I'll test it. Like I said it may just be the better position you can put yourself in.

MaximRecoil · Mar 11, 2011

walrus said:
A few physics or Statics or Dynamics classes I see

It has been a long time since I was in school, but I suspect there are a few things that haven't changed.

By the way, whereabouts in Maine are you located? Dexter here.

walrus · Mar 11, 2011

MaximRecoil said:
It has been a long time since I was in school, but I suspect there are a few things that haven't changed.

By the way, whereabouts in Maine are you located? Dexter here.

Verona. This myth comes up from time to time. Wish I had that screwdriver that produces energy from nothing. I might be able to leave here in the winter :thumbup:

cause that winter has been one for the ages.

Stuey · Mar 11, 2011

MaximRecoil said:
There was an interesting idea in that thread, i.e.:

"3.Improved ability to keep the screwdriver axis closely aligned with
the axis of the screw, thus ensuring the tip of the screwdriver
engages correctly with the slot and is less likely to slip out."

I'd never thought of that, but it is true. This is the same reason that longer barrels on guns with open sights tend to be more accurate. This is not because longer barrels have any inherent accuracy advantage (if anything, shorter barrels are more inherently accurate, all else being equal, because they are more rigid), but rather, the longer barrel allows for a larger sight radius, improving the precision in which one can align the sights, allowing the user to make better use of the available accuracy.

That does make sense as well. You get maximum torque out of a given force if the drive shaft is 100% perpendicular to the fastener as it allows for the applied rotational force and handle radius to be perfectly perpendicular to that as well.

nw2571 said:
There is no "extra" torque being applied through the spring effect. Energy in the system must be conserved. To multiply torque using a spring would be in violation of several physical principles. Springs don't multiply force, they store energy.

The extra length makes the screwdriver less stiff, torsionally (assuming the same shaft cross-section). That is to say for a given amount of torque applied at one end there is more angular deflection over the length of the shaft. This would actually tend to slightly reduce the amount of torque transferred from one end of the driver to the other. Part of the applied torque is used to wind up the spring (shaft) which has some small losses.

This is mostly academic though. The torque limitations of a reasonably designed screwdriver aren't in the shaft anyway. The amount of torque you can apply is limited by either the stiffness of the tip, the screw itself, or the amount of torque a human can input to the screwdriver. The shaft is simply a way to connect the two ends of the screwdriver.

I perhaps chose my words too quickly the first time around, and do happen to agree with your arguments.

I still think that the torsional restoring force will work in the user's favor and/or serve to help prevent tip/fastener damage.

What would your reasoning be for the longer shaft?

mrholeshot · Mar 11, 2011

walrus said:
This myth comes up from time to time. Wish I had that screwdriver that produces energy from nothing.

I argued it to death as a young man. After being proven wrong over and over I finally figured out that some things defy logic. I just went with it and quit over thinking it. If it works it works

garfunkle24 · Mar 11, 2011

nw2571 said:
There is no "extra" torque being applied through the spring effect. Energy in the system must be conserved. To multiply torque using a spring would be in violation of several physical principles. Springs don't multiply force, they store energy.

The extra length makes the screwdriver less stiff, torsionally (assuming the same shaft cross-section). That is to say for a given amount of torque applied at one end there is more angular deflection over the length of the shaft. This would actually tend to slightly reduce the amount of torque transferred from one end of the driver to the other. Part of the applied torque is used to wind up the spring (shaft) which has some small losses.

This is mostly academic though. The torque limitations of a reasonably designed screwdriver aren't in the shaft anyway. The amount of torque you can apply is limited by either the stiffness of the tip, the screw itself, or the amount of torque a human can input to the screwdriver. The shaft is simply a way to connect the two ends of the screwdriver.

Right.

MaximRecoil said:
The energy returned to the screw from what you term as "torsional energy" can not exceed the energy that you put in in the first place. In fact, energy returned from a spring ("torsion bar" type spring in this case) will always be less than what was put in, due to inherent losses. If you have a screwdriver that can create energy then you would easily win the Nobel prize and shatter the foundations of physics as we know it.

Right.

mrholeshot said:
You turn enough screws you figure out what works and what doesn't. Torsional energy, Like Prego it's in there

Wrong.

Even you are governed by the laws of physics, Mr Holeshot. It seems your anecdotal evidence often defies what is logically possible or likely.

mrholeshot · Mar 11, 2011

garfunkle24 said:
Wrong.

Even you are governed by the laws of physics, Mr Holeshot.

Maybe you should read where I said it could be from better position of the screwdriver handle. You work with your short tool, I'll work with some length

garfunkle24 · Mar 11, 2011

mrholeshot said:
Maybe you should read where I said it could be from better position of the screwdriver handle.

I can easily understand the added friction between screw and fastener than can be created by a greater axial load on the driver.

I cannot, however, conceive of a magical mystery force created solely by lengthening the driver.

mrholeshot said:
You work with your short tool, I'll work with some length

So the opposite of usual?

PassnThru · Mar 11, 2011

mrholeshot said:
Maybe you should read where I said it could be from better position of the screwdriver handle. You work with your short tool, I'll work with some length

I'll throw something in on that note. We know larger screws require more torque. Generating your maximum torgue requires optimum positioning of your body and the tool. A longer handle gives you more flexibility to achieve the optimum positioning?

MaximRecoil · Mar 11, 2011

PassnThru said:
I'll throw something in on that note. We know larger screws require more torque. Generating your maximum torgue requires optimum positioning of your body and the tool. A longer handle gives you more flexibility to achieve the optimum positioning?

In some cases I suppose, but generally, the range of motion that the human body has can allow for a position to "lean into it" regardless of shank length. For example, if you are simply screwing a screw into a wide open table, assuming you're not in a back brace, you can "lean into it" whether the shank is 4", 8", or 12". Of course there are times when the screw may be down in the bottom of an engine bay or something and a long screwdriver gives you the extra reach, but there are also times when a longer screwdriver gets in the way (screws under a dash for example).

I'm still of the opinion that a 4" shank is all that's needed for a general purpose screwdriver regardless of the tip size, and it will work fine for most applications; and longer or shorter versions can be selected on an "as needed" basis.

PassnThru · Mar 11, 2011

I see your point. I also think about how a extension bar can be a force multiplier underneath a car when it brings the ratchet down to you instead of being buried up in the chassis.
Of course, I know the real reason. I've just been holding out on you. The longer shank gives you more places to attach the vice grips :thumbup:

A large screw is no more likely to be in a deep hole than a small screw

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