Gears are probably the most efficient method of mechanical power transmission we have today, and much of the reason for that is the shape that gear teeth are ground to.

Unlike the triangular or rectangular teeth you see on comical depictions of gear trains, gear teeth are actually ground to a shape called an "involute".

If you have a string wound around a cylinder, and you keep that string tight as you unwind it from the cylinder, the shape of the curve the end of that string makes is called an "involute". It's a shape similar to a spiral.

The unique advantage of involute gear teeth is that when two involute gear teeth meet, they actually ROLL over each other. That is, the point of contact between the two teeth is a ROLLING contact, not a sliding contact.

And it's this rolling contact made possible by the involute shape of the gear teeth that results in negligible loss of mechanical power to friction, and therefore the excellent mechanical efficiency of gear trains.

If gear teeth slid across each others surface, as is depicted in comical gear trains with rectangular teeth or the "peg" shaped gear teeth you might see on a TV show like "Gilligan's Island", then much of the mechanical power would be lost to friction.

Watch the gear animation at the top of this web page:
Involute gear - Wikipedia, the free encyclopedia

The black dot is the point of contact between the two gear teeth. Note that that dot moves with respect to both teeth as the teeth roll over each other, thereby transmitting force (and hence power) between the gear teeth with negligible friction losses.

So, gear trains are a very efficient way to transport power for much the same reason that passenger and cargo trains are a very efficient way to transport people and goods... ... both benefit from negligible friction losses as a result of a steel-to-steel rolling contact.

On 09/07/2014 10:27 AM, nestork wrote:

Gears are probably the most efficient method of mechanical power
transmission we have today, and much of the reason for that is the shape
that gear teeth are ground to.

Unlike the triangular or rectangular teeth you see on comical depictions
of gear trains, gear teeth are actually ground to a shape called an
"involute".

If you have a string wound around a cylinder, and you keep that string
tight as you unwind it from the cylinder, the shape of the curve the end
of that string makes is called an "involute". It's a shape similar to a
spiral.

The unique advantage of involute gear teeth is that when two involute
gear teeth meet, they actually ROLL over each other. That is, the point
of contact between the two teeth is a ROLLING contact, not a sliding
contact.

And it's this rolling contact made possible by the involute shape of the
gear teeth that results in negligible loss of mechanical power to
friction, and therefore the excellent mechanical efficiency of gear
trains.

If gear teeth slid across each others surface, as is depicted in comical
gear trains with rectangular teeth or the "peg" shaped gear teeth you
might see on a TV show like "Gilligan's Island", then much of the
mechanical power would be lost to friction.

Watch the gear animation at the top of this web page:
'Involute gear - Wikipedia, the free encyclopedia'
(http://en.wikipedia.org/wiki/Involute_gear)

The black dot is the point of contact between any two gear teeth, and
it's the involute shape of the gear teeth allows them to roll over each
other, thereby transmitting power with negligible friction losses.






Thanks for the info

I studied cams and gears as part of my 4th year mechanical engineering course years ago at the U of Manitoba. I've forgotten most of what I learned back then, but I still remember the basic principles. I guess that applies to everything. No matter what you learn, you eventually forget the details, but you always remember the principles.

On 09/07/2014 12:42 PM, nestork wrote:

'philo*[_2_ Wrote:
;3280901']Thanks for the info

I studied cams and gears as part of my 4th year mechanical engineering
course years ago at the U of Manitoba. I've forgotten most of what I
learned back then, but I still remember the basic principles. I guess
that applies to everything. No matter what you learn, you eventually
forget the details, but you always remember the principles.







Well , I was an electrical engineering student so never studied gears...
but I did learn that most of the principles of electrical engineering
could be applied to mechanical engineering (and visa versa)


Perhaps gears and transformers are analogous as they transfer and
convert power efficiently.

On Sun, 7 Sep 2014 17:27:06 +0200, nestork
wrote:


Gears are probably the most efficient method of mechanical power
transmission we have today, and much of the reason for that is the shape
that gear teeth are ground to.

Unlike the triangular or rectangular teeth you see on comical depictions
of gear trains, gear teeth are actually ground to a shape called an
"involute".



Watch the gear animation at the top of this web page:
'Involute gear - Wikipedia, the free encyclopedia'
(http://en.wikipedia.org/wiki/Involute_gear)

The black dot is the point of contact between any two gear teeth, and
it's the involute shape of the gear teeth allows them to roll over each
other, thereby transmitting power with negligible friction losses.

I've never need to know that. But like a lot of other facts, it is
interesting to know. Thanks for posting it. I'll pass it on to a
couple of others that may find it of interest too.

On Sun, 07 Sep 2014 08:27:06 -0700, nestork
wrote:


...snip...excellent fun to read, however...

I feel stupid today, but to me the Wikipedia .gif shows 'constant' speed
transfer, NOT very low friction.

It looked like a lot of sliding along each tooth, but importantly there
was absolutely NO variation in rotational speed for each gear's shaft.

I think I made a big mistake.

To prove to Robert Macy that involute ground gears have a pure rolling contact, I Googled "involute rolling contact" and I got this web page:

http://www.salemcompany.com/cgi-bin/...SSSect1ed2.pdf

...which explains involute gear teeth well... but also says that there's both rolling AND SLIDING between the teeth of involute gears.

That page says the principle advantage of involute ground gear teeth isn't the rolling contact at all, but that involute ground gear teeth allow for constant angular velocity between gears even when the distance between the centers of the gears varies.

I don't know what to say. I was taught that the purpose of the involute shape was to provide for a pure rolling contact between gear teeth, and now when I try to confirm that with online references, I find that's wrong. There is apparantly both rolling and sliding happening at the point where involute ground gear teeth meet.

On 9/7/2014 11:27 AM, nestork wrote:

The unique advantage of involute gear teeth is that when two involute
gear teeth meet, they actually ROLL over each other. That is, the point
of contact between the two teeth is a ROLLING contact, not a sliding
contact.


Years ago, I noticed "hypoid gear oil" for sale at
the auto parts. I asked he twenty something behind
the counter was hypoid gear oil all about. He said
it had to do with the viscosity. I asked a mechanic
who knows a bit out these things, and he explained
that the gears were cut in the shape of a hyperbola,
and that made the energy transfer more efficient.
Hmm.

--
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

Yes, that's a common experience. If you ask any store employee a question, and they don't know the answer, they'll think up one for you.

It's a service they provide free of charge so that their customers don't have to think up an answer themselves.

I kinda feel embarrassed offering up this information on involute gear teeth, and then finding out I was wrong, but I know that no one in here believes that I had anything but the best of intentions.

On 9/8/2014 9:30 AM, nestork wrote:
'Stormin Mormon[_10_ Wrote:
;3281170']
Years ago, I noticed "hypoid gear oil" for sale at
the auto parts. I asked he twenty something behind
the counter was hypoid gear oil all about. He said
it had to do with the viscosity. I asked a mechanic
who knows a bit out these things, and he explained
that the gears were cut in the shape of a hyperbola,
and that made the energy transfer more efficient.
Hmm.


Yes, that's a common experience. If you ask any store employee a
question, and they don't know the answer, they'll think up one for you.

It's a service they provide free of charge so that their customers don't
have to think up an answer themselves.

I kinda feel embarrassed offering up this information on involute gear
teeth, and then finding out I was wrong, but I know that no one in here
believes that I had anything but the best of intentions.

We know you well enough to forgive small
mistayks.

Wish the guy was still there, I'd go ask for a
hypoid-dermic syringe.
http://www.ffx.co.uk/Content/images/tools/AK46.V2.jpg


--
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Mon, 08 Sep 2014 06:30:39 -0700, nestork
wrote:

...snip...

Yes, that's a common experience. If you ask any store employee a
question, and they don't know the answer, they'll think up one for you.

It's a service they provide free of charge so that their customers don't
have to think up an answer themselves.

I kinda feel embarrassed offering up this information on involute gear
teeth, and then finding out I was wrong, but I know that no one in here
believes that I had anything but the best of intentions.



Don't STOP! I saved that little animated gif from Wikipedia. And for the
first time, I marveled out just how difficult true gear design must be.
Think about the vibration potential as the gears wear and the transferring
shaft speed starts to become modulated. Arrgg! And I thought electronics
was fraught with peril.

On Sunday, September 7, 2014 2:23:02 PM UTC-4, philo* wrote:
On 09/07/2014 12:42 PM, nestork wrote:



'philo*[_2_ Wrote:

;3280901']Thanks for the info



I studied cams and gears as part of my 4th year mechanical engineering

course years ago at the U of Manitoba. I've forgotten most of what I

learned back then, but I still remember the basic principles. I guess

that applies to everything. No matter what you learn, you eventually

forget the details, but you always remember the principles.















Well , I was an electrical engineering student so never studied gears...

but I did learn that most of the principles of electrical engineering

could be applied to mechanical engineering (and visa versa)





Perhaps gears and transformers are analogous as they transfer and

convert power efficiently.

I was a math major but worked evenings on a machine that cut the teeth into the gear blanks. Very interesting process.

On 09/08/2014 11:51 AM, Pavel314 wrote:
O








Well , I was an electrical engineering student so never studied gears...

but I did learn that most of the principles of electrical engineering

could be applied to mechanical engineering (and visa versa)





Perhaps gears and transformers are analogous as they transfer and

convert power efficiently.

I was a math major but worked evenings on a machine that cut the teeth into the gear blanks. Very interesting process.




A few of my customers were gear manufacturers so I got to see them being
made.