I would like to find an official ex 3

[ietech]

I would like to find an official explanation of the difference between a "Pulley and a Sheave".

So far throughout the years I have heard several comparisons from back yard engineers and professionals:

1) There is no difference, the terms are inter-changeable. Personally don't think this one is correct. but don't really know. ??????

2) Sheaves drive on the flat inner surface of the belt, thus the sides of a sheave are perpendicular to the diameter (drive surface) between the sides. I Don't think this is accurate based on seening variable sheaves sold with tapered sides.


3) Pulleys are used to drive and be driven by v-belts and cog (synchronous) belts. (????) Maybe????

4) A sheave is used to transfer linear motion i.e a block and tackle; whereas a pulley is used to transfer rotational motion i.e. a belt driven fan unit. I like this one the best but am unsure if it is fact.

Definitions or references to accurate info. is appreciated.

 

[EnglishMuffin]

I love these sorts of questions - they lead to endless discussions with no conclusive outcome, but are very entertainling.

The small dictionary that I have on my desk says :
Pulley : wheel with groove in rim for cord .....
Sheave : grooved wheel of pulley

This is not totally consistent. The second definition seems to imply that a pulley is a wheel plus something else, or was once so defined. The term "pulley wheel" also seems to imply this.

The larger Websters that I have says :

Pulley : a small wheel with a grooved rim .....
a combination of such wheels ...
a wheel that is turned by a belt ....
conical pulley ...
fast pulley .....
loose pulley ....
Sheave : grooved wheel in a pulley block; the wheel of a pulley or any similarly grooved wheel

So on that basis, it looks as though sheaves usually have grooves, but pulleys need not have (most of us know about line shafting with fast and loose pulleys and flat belts).
But to get the full story, you probably need the OED, which would give you the history of these terms - I think sheave is Old English. I expect someone has got an OED - maybe even an on-line subscription. Both of these terms originally predate vee belts, cog belts, etc, but grooved pulleys for rope and cylindrical pulleys with flat belts are both very old, going back to classical times, and so predate the English language, so it should at least be possible to find a precise distinction (if it existed) for the time period when these English words were originally coined. But what really counts is what the majority say is correct today - that will eventually become the dictionary definition, even if it isn't at present.

 

[ietech]

I think you are right about this being a very entertaining. Since I submitted my first post I have spent a couple of hours looking for a definitive answer. Still don't know.

I found some interesting history (the old timers weren't sure either). It appears the terms are commonly used interchangably. To a sailor it means specific type of product. A crane rig is similar but the definitions are different. I really think it comes down to what you do and what part of the world you are from.

It's kinda like Tomato or Tomahto. As long as the person you are talking to understands I guess it doesn't matter.

Thanks for taking the time to answer.

 

[1raven]

The way I understand it, a sheave can be used as a pulley, but it doesn't necessarily have to be.

A sheave is simply a wheel or disk with a grooved rim.
There is no function explicitly implied.
It is no more than a simple object.

A pulley is a sheave (or a collection of sheaves used in combination) that is employed to change direction of pull on a rope, chain or belt, or...
A disk driving or being driven by a belt.
Either way, a pulley implies a specific function.

A pulley is a sheave, but a sheave is not necessarily a pulley.

A sheave is a part of a machine.
A pulley IS a machine.

 

[ietech]

Thank You EnglishMuffin and 1Raven for your responses.

I think I should repost this with a different subject title. I really expected many responses and I think the subject title doesn't really invite folks to express there views.

I will re-post and see if I can get some renewed interest as this is an age old subject and I still haven't been able to find a definitive answer. I think there is really a difference but in this period of history I think it is truly lost.

Thanks Again,
ietech

 

[involute]

i think that it is just a matter of language in the end they are just both the same

We in india call them pulleys and had a customer come in from USa who was calling them sheaves and i was wondering what the heck is he talking about !!!!!!

till it hit me that a pulleyand a sheave is one and the same !!!!!

 

[Neilmo]

ietech,

I use both pulleys and sheaves in my work and my understanding is -

A sheave is used for `driving`, whereas a pulley is `driven`, or used for `diverting`. In other words, an electric motor would have a sheave on it to drive some piece of equipment. While a pulley would be on the piece of equipment being driven. On a crane a pulley would be used to divert the cable.

Having said that, both pulleys and sheaves often have the same dimensions, so physically there is not necessarily any difference. The terminology being governed only by where the pulley / sheave is being used.

Regards,
Neilmo

 

[ietech]

Nielmo,

Thanks for the response. Your explaination is one that is very similar to my preferred definition, actually I like yours better.

 

[Neilmo]

Thank you for the star ietech, it is greatly appreciated and I am glad to be of help.

Neilmo