Re: Snaping Spokes

Jim Smith said:

Quoted message said:

Werehatrack said:

On Sat, 05 Mar 2005 22:28:40 -0700, [email hidden] may have
said:

>On Sun, 06 Mar 2005 05:13:42 GMT, "Leo Lichtman"
><[email hidden]> wrote:
>
>>4,) Steel wheel with steel spokes--stronger and lighter than cast iron
>>wheel. Insight that the upper spokes are carrying tension.
>^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^?
>>5.) Steel wheel with thin spokes, in which both compression and tension are
>>developed.
>>6.) Wheel with wire spokes.
>
>Dear Leo,
>
>It's the step between 4 and 5 that's puzzling.
>
>The upper spokes in a compression wheel shouldn't show
>tension, should they?

I looked closely at a couple of very old implement wheels a while
back, and was a bit surprised to see that in the case of these
particular ones, the spokes were not welded to the rim, but rather
passed through it and upset on the outer side. I have no idea how old
they were, nor where they came from or what the brand of item was that
they were on; they were in a collection of disused farm equipment that
was being sold for its value as antiques and decorations. It's quite
possible that there was no actual tension on the spokes at rest, and
they may have been made with a shoulder that butted against the inside
of the rim; I didn't think to look for that. Still, the germ of the
idea may have been present.

>I think that you should be able to cut off everything just
>above 3 and 9 o'clock on such a wheel when motionless.

In a perfect world, perhaps, but a spoked wooden wagon wheel without
compression from its band will collapse *sideways* in short order.
That's according to a wheelwright who makes them for some of the
wagons that are used in the annual Trail Rides that are tradtional in
the week leading to the opening of the Houston Livestock Show and
Rodeo.

>Maybe there's a little tension or compression in the upper
>spoke of a wooden/iron compression wheel?

More than a little, from what he was saying.

Dear Werehatrack,

Yes, load-bearing wooden wheels like wagon wheels are
compressed and dished by the shrunk-on metal rim strip. The
dishing is needed for the side-loads of 4-wheel wagons (they
have a nasty habit of failing sideways).

The compression of the metal rim strip is needed just to
hold the wheel together--without it, the sections fly apart
at any speed. There's some mortise work, but the tapered
spokes are just jammed into holes bored into the separate
curved sections of wood that make up the rim. It's
tinker-toy construction that needs a rubber band just to
hold it together.

But the spoke load is carried entirely by further
compression by the lower wooden spoke--if anything, the
upper wooden spoke might experience a little decompression,
but I don't think that this would amount to anything like
"hanging from the upper spoke" in the sense of a pre-tension
wheel "standing" on its lower spoke.

Bicycle wheels function the same as wagon wheels. Pre-tensioning the
spokes does two important structural things: 1) it prevents the spokes
from buckling. 3) it allows the connections at nipple and hub to work.

It is instructive to note that it is not necessary to tension the
spokes in a computer model if one is only interested in which spokes
carry the load.

Dear Jim,

It is, however, necessary to compress a wooden wagon wheel.
Otherwise, it falls apart.

Bicycle spokes are in tension. When the lower spokes lose
tension dramatically, the upper spokes do gain tension
slightly (not nearly enough to match the loss in the lower
spokes).

But wagon wheel spokes are in compression--an iron band is
shrunk onto the rim formed by multiple wheel sections and
holds everything together like a rubber band. When the lower
spoke compresses and the lower rim flattens slightly,
tension is lost in the band, so it seems possible that the
upper wooden spoke actually loses compression and expands
slightly.

As for your last point, I think that you're mistaken. It is
necessary to have tension on a computer model of a
pre-tensioned bicycle wheel, just as it's necessary for a
real wheel--if there is no initial tension, there's none to
be lost by the lower spoke contracting when the lower part
of the rim deflects.

If not tensioned to begin with, the lower spoke would simply
rattle around loose when a load was put on the hub, and the
hub would indeed hang from the upper spokes.

But that's not a pre-tensioned bicycle wheel, as poor Jobst
has to keep pointing out.

You may be thinking of solidly connected strut-spokes, like
a single-piece cast control wheel. Since those spokes are
not free to dangle out the bottom of a rim like bicycle
spokes, they work as you suggest.

Carl Fogel

Quoted message said:

As for your last point, I think that you're mistaken. It is
necessary to have tension on a computer model of a
pre-tensioned bicycle wheel, just as it's necessary for a
real wheel--if there is no initial tension, there's none to
be lost by the lower spoke contracting when the lower part
of the rim deflects.

The relationship between length and force in the spokes is linear,
there is no need to model the preload. Superposition is real, it
works.

To simulate the effects of tension in the spoke it is only necessary
to constrain the spoke ends to remain in contact with the hub and rim,
and to eliminate buckling from the spokes.

Neil Brooks said:

Tim McNamara said:

Gee, the OP seems suddenly to have dropped out of sight. You think
maybe this was a troll?

My guess is that the OP just never got the answer to the question
posed in his/her subject, "Snaping Spokes."

To snape, you see, is (in shipbuilding parlance) to bevel the end of a
timber to fit against an inclined surface.

I presume the OP left in frustration while we spoke about this
seemingly unrelated stuff.

Ahhh, now I see the connection.

Think about how the rim end of the wooden wagon wheel spoke is prep'd
to fit into the inside of the rim... snaped, indeed.

So the OP was actually asking about how to build a wagon wheel, and
we've probably just annoyed him/her with all this talk about wire
spokes.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

"Mark Hickey" wrote: (clip) So the OP was actually asking about how to
build a wagon wheel, and we've probably just annoyed him/her with all this
talk about wire spokes.
^^^^^^^^^^^^^^
I've thumbed through Jobst's book twice, and cannot find a word about wagon
wheels or wooden spokes. Is there a rec.wagons.tech group?

Jim Smith said:

Quoted message said:

As for your last point, I think that you're mistaken. It is
necessary to have tension on a computer model of a pre-tensioned
bicycle wheel, just as it's necessary for a real wheel--if there is
no initial tension, there's none to be lost by the lower spoke
contracting when the lower part of the rim deflects.

Quoted message said:

The relationship between length and force in the spokes is linear,
there is no need to model the preload. Superposition is real, it
works.

Quoted message said:

To simulate the effects of tension in the spoke it is only necessary
to constrain the spoke ends to remain in contact with the hub and
rim, and to eliminate buckling from the spokes.

I'm getting deja-vu all over again. I have tried to explain this over
the years to no apparent effect just as the concept that all spoked
wheels support loads in the same manner. To emphasize this
graphically as well as in words, "the Bicycle Wheel" has a picture of
a wooden wagon wheel as well as a die cast aluminum wheel that appears
to be a wire spoked wheel but isn't. None of these wheels need to
have their pre-condition given in the FEA model.

This concept has been rehashed many times on this forum.

Jobst Brandt
[email hidden]

Jim Smith said:

Quoted message said:

As for your last point, I think that you're mistaken. It is
necessary to have tension on a computer model of a
pre-tensioned bicycle wheel, just as it's necessary for a
real wheel--if there is no initial tension, there's none to
be lost by the lower spoke contracting when the lower part
of the rim deflects.

The relationship between length and force in the spokes is linear,
there is no need to model the preload. Superposition is real, it
works.

To simulate the effects of tension in the spoke it is only necessary
to constrain the spoke ends to remain in contact with the hub and rim,
and to eliminate buckling from the spokes.

Dear Jim,

How do you constrain a spoke at the nipple end in a real
bicycle wheel? If it isn't pretensioned, it moves
effortlessly into space with the slightest push.

Carl Fogel

Leo Lichtman said:

"Mark Hickey" wrote: (clip) So the OP was actually asking about how to
build a wagon wheel, and we've probably just annoyed him/her with all this
talk about wire spokes.
^^^^^^^^^^^^^^
I've thumbed through Jobst's book twice, and cannot find a word about wagon
wheels or wooden spokes. Is there a rec.wagons.tech group?

Dear Leo,

Note the sections, wooden spokes, and hot-shrunk 1" x 1/8"
steel (an improvement) band:

http://www.wagons-wheels.com/p3260020.html

No dish in this model.

Some are a bit larger than the penny-farthing:

http://www.wagons-wheels.com/whatinwor.html

Here's the enlarged picture, showing the coompressive bands:

http://store1.yimg.com/I/wagon-wheel_1803_8204579

Carl Fogel

Leo Lichtman said:

"Mark Hickey" wrote: (clip) So the OP was actually asking about how to
build a wagon wheel, and we've probably just annoyed him/her with all this
talk about wire spokes.
^^^^^^^^^^^^^^
I've thumbed through Jobst's book twice, and cannot find a word about wagon
wheels or wooden spokes. Is there a rec.wagons.tech group?

Dear Leo,

Here's the wooden wagon-wheel equivalent of "The Bicycle
Wheel":

http://www.wagons-wheels.com/bd113.html

Otherwise, you can google here:

http://groups.google.co.uk/groups?hl=en&lr=&group=rec

for "wooden wheel" and "wagon" and find some posts in the
woodworking and metalworking groups.

Carl Fogel

Jobst Brandt said:

Jim Smith said:

Quoted message said:

As for your last point, I think that you're mistaken. It is
necessary to have tension on a computer model of a pre-tensioned
bicycle wheel, just as it's necessary for a real wheel--if there is
no initial tension, there's none to be lost by the lower spoke
contracting when the lower part of the rim deflects.

Quoted message said:

The relationship between length and force in the spokes is linear,
there is no need to model the preload. Superposition is real, it
works.

Quoted message said:

To simulate the effects of tension in the spoke it is only necessary
to constrain the spoke ends to remain in contact with the hub and
rim, and to eliminate buckling from the spokes.

I'm getting deja-vu all over again. I have tried to explain this over
the years to no apparent effect just as the concept that all spoked
wheels support loads in the same manner. To emphasize this
graphically as well as in words, "the Bicycle Wheel" has a picture of
a wooden wagon wheel as well as a die cast aluminum wheel that appears
to be a wire spoked wheel but isn't. None of these wheels need to
have their pre-condition given in the FEA model.

This concept has been rehashed many times on this forum.

Apparently the deceased equine has not been sufficiently flagellated.

--
Tom Sherman - Earth

Leo Lichtman wrote: I've thumbed through Jobst's book twice, and cannot find
a word about wagon
wheels or wooden spokes. Is there a rec.wagons.tech group?

<[email hidden]> wrote: (clip) "the Bicycle Wheel" has a
picture of a wooden wagon wheel (clip)
^^^^^^^^^^^^^^^^
I stand corrected. I guess I'd better look again.

Quoted message said:

Jim Smith said:

Quoted message said:

As for your last point, I think that you're mistaken. It is
necessary to have tension on a computer model of a pre-tensioned
bicycle wheel, just as it's necessary for a real wheel--if there is
no initial tension, there's none to be lost by the lower spoke
contracting when the lower part of the rim deflects.

Quoted message said:

The relationship between length and force in the spokes is linear,
there is no need to model the preload. Superposition is real, it
works.

Quoted message said:

To simulate the effects of tension in the spoke it is only necessary
to constrain the spoke ends to remain in contact with the hub and
rim, and to eliminate buckling from the spokes.

I'm getting deja-vu all over again. I have tried to explain this over
the years to no apparent effect just as the concept that all spoked
wheels support loads in the same manner. To emphasize this
graphically as well as in words, "the Bicycle Wheel" has a picture of
a wooden wagon wheel as well as a die cast aluminum wheel that appears
to be a wire spoked wheel but isn't. None of these wheels need to
have their pre-condition given in the FEA model.

Right, but some boundry conditions are implicit in the model, of
course. Your book describes a 37 node 2d model and a 72 node 2d
model. The rim ends of the spokes share the same 36 nodes which make
up the rim in your model. That is what I meant by "constrain the
spoke ends to remain in contact with the rim."

Similarly, it seems to be common to model the spokes as a single
element between two nodes. One write up on the web, for example, uses
an ANSYS LINK8 element to model the spokes. The "no buckling"
constraint is implicit in the use of this element.

Quoted message said:

Jim Smith said:

Quoted message said:

As for your last point, I think that you're mistaken. It is
necessary to have tension on a computer model of a
pre-tensioned bicycle wheel, just as it's necessary for a
real wheel--if there is no initial tension, there's none to
be lost by the lower spoke contracting when the lower part
of the rim deflects.

The relationship between length and force in the spokes is linear,
there is no need to model the preload. Superposition is real, it
works.

To simulate the effects of tension in the spoke it is only necessary
to constrain the spoke ends to remain in contact with the hub and rim,
and to eliminate buckling from the spokes.

Dear Jim,

How do you constrain a spoke at the nipple end in a real
bicycle wheel? If it isn't pretensioned, it moves
effortlessly into space with the slightest push.

You constrain it by pretensioning it.

That is what I meant by saying that pretensioning the spokes allows
the joints at the hub and rim to work.

Werehatrack said:

On Sun, 06 Mar 2005 18:39:27 -0700, [email hidden] may have

Quoted message said:

Durability aside, we may not be thinking of the same design
yet. I'm thinking of a tinker-toy assembly of tapered wooden
spokes stuck into a hub, shod with wooden wheels sections,
which are in turn compressed by a shrunk-on iron band.

I was under the impression that the specific type for this subthread
was an all-iron implement wheel with welded spokes, in which I really
doubt there's enough spoke compression to cause any tension change
anywhere in the wheel.

Compression-band wood wheels are also very stiff. If there's any
flattening, it's probably going to be just the amount permitted by the
wood in the immediate vicinity; not much, if any. I doubt that you'd
measure any change in the compression elsewhere in the wheel with
those, either.

While I have significant respect for you and your contributions to
this forum, this verges on snape sniping.

;-)

On Sun, 06 Mar 2005 18:39:27 -0700, [email hidden] may have

Quoted message said:

Durability aside, we may not be thinking of the same design
yet. I'm thinking of a tinker-toy assembly of tapered wooden
spokes stuck into a hub, shod with wooden wheels sections,
which are in turn compressed by a shrunk-on iron band.

I was under the impression that the specific type for this subthread
was an all-iron implement wheel with welded spokes, in which I really
doubt there's enough spoke compression to cause any tension change
anywhere in the wheel.

Compression-band wood wheels are also very stiff. If there's any
flattening, it's probably going to be just the amount permitted by the
wood in the immediate vicinity; not much, if any. I doubt that you'd
measure any change in the compression elsewhere in the wheel with
those, either.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

(clip) this verges on snape sniping.
^^^^^^^^^^^^^^^
And THIS is snape snipe snooping.

Werehatrack said:

On Mon, 07 Mar 2005 19:31:49 GMT, "Leo Lichtman"

may have said:

(clip) this verges on snape sniping.
^^^^^^^^^^^^^^^
And THIS is snape snipe snooping.

No need to get snippy...

Or to snap at the guy...

On Mon, 07 Mar 2005 19:31:49 GMT, "Leo Lichtman"

may have said:

(clip) this verges on snape sniping.
^^^^^^^^^^^^^^^
And THIS is snape snipe snooping.

No need to get snippy...

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

S o r n i said:

Werehatrack said:

On Mon, 07 Mar 2005 19:31:49 GMT, "Leo Lichtman"

may have said:

(clip) this verges on snape sniping.
^^^^^^^^^^^^^^^
And THIS is snape snipe snooping.

No need to get snippy...

Or to snap at the guy...

He wasn't. I verified that on Snopes.

Tim McNamara said:

Gee, the OP seems suddenly to have dropped out of sight. You think
maybe this was a troll?

His disappearance is otherwise inexplicable, especially when you
consider that the Chairman of the RBT Membership Committee took time
to send him a personalized 'welcome' message.
-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Comprehensive catalogue of track equipment: online since 1996.
http://www.businesscycles.com

Werehatrack said:

On Sun, 06 Mar 2005 18:39:27 -0700, [email hidden] may have

Quoted message said:

Durability aside, we may not be thinking of the same design
yet. I'm thinking of a tinker-toy assembly of tapered wooden
spokes stuck into a hub, shod with wooden wheels sections,
which are in turn compressed by a shrunk-on iron band.

I was under the impression that the specific type for this subthread
was an all-iron implement wheel with welded spokes, in which I really
doubt there's enough spoke compression to cause any tension change
anywhere in the wheel.

Compression-band wood wheels are also very stiff. If there's any
flattening, it's probably going to be just the amount permitted by the
wood in the immediate vicinity; not much, if any. I doubt that you'd
measure any change in the compression elsewhere in the wheel with
those, either.

Dear Werehatrack,

Yes, I think that there's been some confusion in this
thread, with some posts not distinguishing between newer
all-metal welded and old-fashioned wooden-spoke
pre-compressed-by-shrunk-band (as opposed to pre-tensioned
by spoke).

I really have no idea whether there's any change in the
tension of the pre-shrunk band (lose or gain) on a wooden
pre-compressed wheel.

But we do have the calculations and tests that show that the
upper spokes on a pre-tensioned wheel do change slightly,
gaining a few pounds of tension--so I wonder what the
sorta-kinda reverse design does, when the rim supplies the
compression to stiff wooden spokes rather than being
compressed by tension from elastic metal spokes.

As for how much permitted by the wood, I have no idea how
much the wooden rim (or maybe just an individual section)
would deflect, but the typical wagon load is much higher
than the load on a bicycle wheel. Something's gotta squash,
and that may in turn affect the rest of the wheel.

Carl Fogel