What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?

thunk fired this volley in
:

What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?

You increase any inherent 'play' in the system. Also since the 'middle
race' is no longer heat-sunk to a shaft or housing, risk the possibility
of heating it without any way to remove the heat.

OTOH, you've distributed the wear over at least twice as many rolling
elements, and if everything were perfect the balls and races would turn
more slowly than a conventional bearing. IF everything were perfect.

Lloyd

On 3/31/2014 8:08 AM, Lloyd E. Sponenburgh wrote:
fired this volley in
:

What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?
You increase any inherent 'play' in the system. Also since the 'middle
race' is no longer heat-sunk to a shaft or housing, risk the possibility
of heating it without any way to remove the heat.

OTOH, you've distributed the wear over at least twice as many rolling
elements, and if everything were perfect the balls and races would turn
more slowly than a conventional bearing. IF everything were perfect.

Lloyd

I always thought that would be like two resistors in parallel as far as
friction goes?

On Mon, 31 Mar 2014 08:08:20 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

thunk fired this volley in
:

What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?

You increase any inherent 'play' in the system. Also since the 'middle
race' is no longer heat-sunk to a shaft or housing, risk the possibility
of heating it without any way to remove the heat.

And play = vibrations, most usually. Also, how do you securely secure
an outer bearing race into an inner bearing race? You can't squeeze
either. You can't heat it to red hot to interference-fit it. And glue
isn't strong enough.

OTOH, you've distributed the wear over at least twice as many rolling
elements, and if everything were perfect the balls and races would turn
more slowly than a conventional bearing. IF everything were perfect.

I would think the smaller bearing would take most of the revolutions
due to its lower friction surfaces. That might allow a faster spin,
but with the added vibration from play, it might result in a truly
spectacular catastrophic disintegration, too. I wouldn't want my
hands/eyes/body anywhere near it when that happened.

I wouldn't do it.

--
I would be the most content if my children grew up to be the kind of people
who think decorating consists mostly of building enough bookshelves.
-- Anna Quindlen

"Larry Jaques" wrote in message
...
On Mon, 31 Mar 2014 08:08:20 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

thunk fired this volley in
m:

What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?

You increase any inherent 'play' in the system. Also since the 'middle
race' is no longer heat-sunk to a shaft or housing, risk the possibility
of heating it without any way to remove the heat.

And play = vibrations, most usually. Also, how do you securely secure
an outer bearing race into an inner bearing race? You can't squeeze
either. You can't heat it to red hot to interference-fit it. And glue
isn't strong enough.

For purely academic purposes its not that hard. You use a bushing in
between the two races. Depending on the bearing type and application a
double lipped bushing so when you apply force in one direction it presses
against the inner lip of the bushing, and the outer lip pushes against the
inner race of the outer bearing.

For practical reasons I wonder about the application. A high speed spindle
of some kind? I imagine run out would be pretty bad, but it might be able
to handle more load than a single ceramic bearing to run the same speed.







OTOH, you've distributed the wear over at least twice as many rolling
elements, and if everything were perfect the balls and races would turn
more slowly than a conventional bearing. IF everything were perfect.

I would think the smaller bearing would take most of the revolutions
due to its lower friction surfaces. That might allow a faster spin,
but with the added vibration from play, it might result in a truly
spectacular catastrophic disintegration, too. I wouldn't want my
hands/eyes/body anywhere near it when that happened.

I wouldn't do it.

--
I would be the most content if my children grew up to be the kind of
people
who think decorating consists mostly of building enough bookshelves.
-- Anna Quindlen

"Bob La Londe" wrote in message
...
"Larry Jaques" wrote in message
...
On Mon, 31 Mar 2014 08:08:20 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

thunk fired this volley in
:

What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?

You increase any inherent 'play' in the system. Also since the 'middle
race' is no longer heat-sunk to a shaft or housing, risk the possibility
of heating it without any way to remove the heat.

And play = vibrations, most usually. Also, how do you securely secure
an outer bearing race into an inner bearing race? You can't squeeze
either. You can't heat it to red hot to interference-fit it. And glue
isn't strong enough.

For purely academic purposes its not that hard. You use a bushing in
between the two races. Depending on the bearing type and application a
double lipped bushing so when you apply force in one direction it presses
against the inner lip of the bushing, and the outer lip pushes against the
inner race of the outer bearing.

For practical reasons I wonder about the application. A high speed
spindle of some kind? I imagine run out would be pretty bad, but it might
be able to handle more load than a single ceramic bearing to run the same
speed.


Another thought based on bearing type... If they are tapered roller bearings
with axial pressure the central race could be tapered one way for the outer
and the other for the inner. I suppose an ACB could be designed the same
way as well.











OTOH, you've distributed the wear over at least twice as many rolling
elements, and if everything were perfect the balls and races would turn
more slowly than a conventional bearing. IF everything were perfect.

I would think the smaller bearing would take most of the revolutions
due to its lower friction surfaces. That might allow a faster spin,
but with the added vibration from play, it might result in a truly
spectacular catastrophic disintegration, too. I wouldn't want my
hands/eyes/body anywhere near it when that happened.

I wouldn't do it.

--
I would be the most content if my children grew up to be the kind of
people
who think decorating consists mostly of building enough bookshelves.
-- Anna
Quindlen

On Mon, 31 Mar 2014 09:27:40 -0500, Richard wrote:

On 3/31/2014 8:08 AM, Lloyd E. Sponenburgh wrote:
fired this volley in
:

What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?
You increase any inherent 'play' in the system. Also since the 'middle
race' is no longer heat-sunk to a shaft or housing, risk the
possibility of heating it without any way to remove the heat.

OTOH, you've distributed the wear over at least twice as many rolling
elements, and if everything were perfect the balls and races would turn
more slowly than a conventional bearing. IF everything were perfect.

Lloyd

I always thought that would be like two resistors in parallel as far as
friction goes?

Nope. That would be true if the friction in a ball bearing were
proportional to velocity. It's not -- when everything is sitting still
the two shafts act like they're connected with a spring. Then, once
there's enough force to get the balls rolling (as it were) there's a
relatively constant friction force. There is a small element of friction
that rises with velocity, but it's not usually very big.

I know the gory detail on this from stabilizing gimballed platforms that
have to hang from helicopters. One of the biggest paths by which the
aircraft motion gets into the platform is through the bearings, and one
of the biggest tradeoffs (once you're buying the World's Most Expensive
Bearings) ends up in bearing strength vs. bearing friction -- basically,
the more load the bearing can bear, the more friction it has.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On Mon, 31 Mar 2014 08:08:20 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

thunk fired this volley in
:

What happens if you put a bearing within a bearing - the outer race of
the inside one being the inner race of the outside one? Is friction
reduced? Is the maxiumum speed changed? Temp rise?

You increase any inherent 'play' in the system. Also since the 'middle
race' is no longer heat-sunk to a shaft or housing, risk the possibility
of heating it without any way to remove the heat.

OTOH, you've distributed the wear over at least twice as many rolling
elements, and if everything were perfect the balls and races would turn
more slowly than a conventional bearing. IF everything were perfect.

Lloyd

Early Royal Enfield motorcycles had a connecting rod bearing that was
free to move both in the rod big end and on the crankshaft.
--
Cheers,

John B.