Curved Handles: Mechanics Behind the Design

[BurnIt0017]

Hi, why did they make the handles curved? Is there a mechanical advantage?

 

[pukb]

In order to create a higher moment (higher mech adv) it is designed like that. If it were straight as seen usually, it would create moment which is a multiple (sin x) of what is created here. hence Mech Adv is increased by sinx times.
above explanation is true when force is applied normal to handle.

 

[BurnIt0017]

Hi, the reason why I ask is I am working on a vertical axis wind turbine project. I am looking for away to increase the start up torque. If the blade rotor spokes had a similar configuration would it be beneficial?

 

[mfb]

In order to create a higher moment (higher mech adv) it is designed like that. If it were straight as seen usually, it would create moment which is a multiple (sin x) of what is created here. hence Mech Adv is increased by sinx times.
above explanation is true when force is applied normal to handle.

Assuming you can apply the same force for both designs, and the end of the handle is perpendicular to the lever arm (which is true for a straight handle, and maximizes torque), torque is just determined by the length of the lever arm - and that does not increase with a curved handle.

 

[phinds]

It's strictly ergonomics ... fits the hand better. As mfb stated, the idea that the curve changes the torque is just silly

 

[BurnIt0017]

Thank you

 

[Ranger Mike]

Bemis & Call was an early maker of tools and hardware dating back to an 1844 partnership between Stephen C. Bemis and Amos Call. The company produced a variety of tools including pipe wrenches, monkey wrenches, and other adjustable wrenches, and was especially well known for their S-shaped adjustable wrenches.
The S handle is NOT for ergonomics as the 1844 introduction shows..it is to be able to " snake' into tight restrictive appliactions where the straight handel does not permit tightening or lossening of the nut or pipe flange. I have had to use a propane torch to heat and bend open end wrenchs on many occassions due to very limited room t o swing the wrench.

 

[phinds]

Bemis & Call was an early maker of tools and hardware dating back to an 1844 partnership between Stephen C. Bemis and Amos Call. The company produced a variety of tools including pipe wrenches, monkey wrenches, and other adjustable wrenches, and was especially well known for their S-shaped adjustable wrenches.
The S handle is NOT for ergonomics as the 1844 introduction shows..it is to be able to " snake' into tight restrictive appliactions where the straight handel does not permit tightening or lossening of the nut or pipe flange. I have had to use a propane torch to heat and bend open end wrenchs on many occassions due to very limited room t o swing the wrench.

And in what way is that not ergonomics ?

 

[Ranger Mike]

Ok I realize that the action of fabricating a tool to better access a particular application may be covered under todays definition of Ergonomics. That was not the purpose of designing the S handle. Its introduction pre-dated the first documented introduction of the subject.

The term ergonomics, from Greek Έργον, meaning "work", and Νόμος, meaning "natural laws", first entered the modern lexicon when Wojciech Jastrzębowski used the word in his 1857 article Rys ergonomji czyli nauki o pracy, opartej na prawdach poczerpniętych z Nauki Przyrody (The Outline of Ergonomics, i.e. Science of Work, Based on the Truths Taken from the Natural Science).[3] The introduction of the term to the English lexicon is widely attributed to British psychologist Hywel Murrell, at the 1949 meeting at the UK's Admiralty, which led to the foundation of The Ergonomics Society. He used it to encompass the studies in which he had been engaged during and after the World War II.[4]
Since the first patented S handle wrench was in 1844,,,I submit that its purpose was not to address Ergonomics but to remedy one particular requirment of the day...and my best guess was locomotive..
I am sure you are much more versed on this subject than I. I am merely a wrench bender with a college degree and defer to your knowledge...

 

[phinds]

Since the first patented S handle wrench was in 1844,,,I submit that its purpose was not to address Ergonomics but to remedy one particular requirment of the day...and my best guess was locomotive..

You are picking nits. Yes, it was ergonomics before the name was invented, but that does not stop it from being ergonomics.

I am sure you are much more versed on this subject than I. I am merely a wrench bender with a college degree and defer to your knowledge...

The snotty attitude is not necessary.

 

[Ranger Mike]

ok , leaving attitudes aside.,..and so I can learn..

please define ergonomics.

 

[phinds]

In common usage (I'm not even going to bother with a dictionary lookup) it just means design that enhances the experience for the user or makes something easier for a person to use. It doesn't change the basic functionality.

For example, really well designed chairs can be a lot more pleasant to sit in, expecially for hours at a time, than a simple straight-back chair, but they are both just chairs and have exactly the same function.

I think in the case of a S shape being used to ALLOW the tool to work (as opposed to making it more comfortable to grip), it may NOT be ergonomics and I spoke too soon because I have a prefernce for those grips (they ARE more comfortable to use) but have never had to use them in a place where the S was needed for functionality. That is, it turns out to be an ergonomic design even though it was not specifically added for that purpose.

Also, I was responding to the OP's belief that it might be a force enhancement thing, which it clearly is not.

 

[russ_watters]

The crank handle is probably just curved for aesthetics.

The adjustable wrench does provide a potential "force advantage" in that if you pull toward the wrench, it pushes the wrench onto the nut, which may help keep it from slipping off. You may notice that a modern adjustable wrench is angled (just not curved):

http://upload.wikimedia.org/wikipedia/commons/5/55/Adjustable_wrench.svg

 

[phinds]

The crank handle is probably just curved for aesthetics.

I think you must have overlooked the statement about how the S was needed to get the wrench to fit around pipes and stuff.

 

[russ_watters]

I think you must have overlooked the statement about how the S was needed to get the wrench to fit around pipes and stuff.

I think you missed the words "crank handle" in the sentence you quoted... That's the object on the right in the picture. It isn't a wrench. It looks like the handle of an old meat grinder:

http://www.neaca.com/images/Win_grinder_2_.JPG

 

[phinds]

I think you missed the words "crank handle" in the sentence you quoted... That's the object on the right in the picture. It isn't a wrench. It looks like the handle of an old meat grinder:

Obviously I did miss it. Sorry, and thanks for pointing that out.

 

[AlephZero]

It looks like the handle of an old meat grinder:

19th century mech engineers seemed to have an thing about curved spokes rather than straight ones. I suspect they came up with some wrong idea about forces "flowing smoothly" from the spokes into the rim. Of course tangential spokes at the hub (as in modern bike wheels) are a geuninely good idea, but that doesn't seem to be what they were aiming at...

 

[pantaz]

I can't cite a source, but I believe the superfluous curves were generally just for aesthetics. However, I would not be surprised if some were believed to add mechanical advantage.

Examples of artistic design can be found on many antique machines and tools. You must remember that they were created by true craftsmen, who often added embellishments as a "signature", or to otherwise demonstrate their expertise.

 

[Ranger Mike]

Thanks you Phinds...well stated.

 

[256bits]

19th century mech engineers seemed to have an thing about curved spokes rather than straight ones. I suspect they came up with some wrong idea about forces "flowing smoothly" from the spokes into the rim. Of course tangential spokes at the hub (as in modern bike wheels) are a geuninely good idea, but that doesn't seem to be what they were aiming at...

Curved spokes from hub to rim was one method as casting technique designed to counteract the stresses induced within the metal shunk in volume as it cooled from liquid to solid. Straight spokes would crack either the hub or rim, or fail early in use.

Contrast that with the 19th century of assembled straight wooden spokes for carriage wheels.

 

[Ranger Mike]

now this makes perfect sense. that is why this forum is so valuable..good point and thank you!