Break down, go ahead and give it to me.



Ken Cline wrote:
> *In response to your question, I calculated the (relative) strength of
> the axle. The short answer is tubes are really quite strong and you
> only lose about 8% of the strength by hollowing out the axle.*
Does this mean that by hollowing out the center of a forged or machined
piece of cold rolled or other material that you should only lose about
8% of strength?

I think I can accept that number as believable. But I also believe it's
8% too much. Square taper axles can't afford to give anything away.

> *The long answer is that bending strength is limited by the maximum
> stress exterted on the axle, which will be at the outside of the bend
> (in a smooth walled tube). For hollow axles, that stress is
> proportional to
> T / (od^4 -id^4) *
All those numbers were very cool, and I won't claim to have followed it
all. But it seems like you were calculating strength based on some fixed
set of parameters.

Unicycle axles break gradually. That's why the age-old question of "how
high of drops can I do?" never makes sense. It's not how high, it's how
many (x how hard).

As was described in later threads, many axles have been known to "twist"
before breaking off. I've seen this on my own and others. When
cotterless cranks are suddenly no longer at 180 degrees to each other,
it usually means your axle is going to let go in the near future.


--
johnfoss - Walkin' on the edge

John Foss, the Uni-Cyclone
"jfoss" at "unicycling.com"
www.unicycling.com

"Hey, could I have some of that spinach? I need to get this pork rind
taste out of my mouth." -- Ryan Atkins to Kris Holm, on the way back
from Moab after sampling some of my pork rinds. They grossed out the
whole van!
------------------------------------------------------------------------
johnfoss's Profile: http://www.unicyclist.com/profile/832
View this thread: http://www.unicyclist.com/thread/31905
 
johnfoss wrote:
> *As was described in later threads, many axles have been known to
> "twist" before breaking off. I've seen this on my own and others. When
> cotterless cranks are suddenly no longer at 180 degrees to each other,
> it usually means your axle is going to let go in the near future. *

I wonder if there aren't already cracks by the time twisting becomes
noticable. I.e. Is the twisting happening because the spindle is no
longer a solid piece due to the presence of cracks? Or, is the spindle
still solid, but just so weakened (by repeated stresses) that it is
deforming?


--
duaner - -

duaner.
------------------------------------------------------------------------
duaner's Profile: http://www.unicyclist.com/profile/4297
View this thread: http://www.unicyclist.com/thread/31905
 
"johnfoss" <[email protected]> writes:

> Does this mean that by hollowing out the center of a forged or machined
> piece of cold rolled or other material that you should only lose about
> 8% of strength?

Yes, that's my extimate for that axle. Of couurse if you change the
size of the hole, the strength loss will change too.

There is another I didn't mention before. My calculation is for the
torque twisting the axle on its axis. There is also a component
twisting it down towards the ground (between bearing and crank).
Still, when we land with the cranks horizontal, there should be much
more torque along the axle than down towards the ground.

> I think I can accept that number as believable. But I also believe it's
> 8% too much. Square taper axles can't afford to give anything away.

True. I think I said something to that effect. We don't need
equations to come to this comclusion - the results of this multiple
break down are ample evidence.

Of course if manufacturers used exotic ultra-high-strength steel, hubs
could be twice as strong or more. But then they wouldn't sell for
$25.

> > *The long answer is that bending strength is limited by the maximum
> > stress exterted on the axle, which will be at the outside of the bend
> > (in a smooth walled tube). For hollow axles, that stress is
> > proportional to
> > T / (od^4 -id^4) *
> All those numbers were very cool, and I won't claim to have followed it
> all. But it seems like you were calculating strength based on some fixed
> set of parameters.

Sorry if I didn't make it properly clear. I enlarged the picture of
the broken axle and measured the inner- and outer-diameters on my
computer screen. Crude, but sufficient for a ballpark estimate. That
where I came up with 4.3w and 2.3w for the outside and inside
diameters of the axle. The formula T / (od^4 - id^4) is a
simplification of an engineering formula made by removing constant
factors. The resulting comparison is identical to the more complex
form since the factors cancel during division.

> Unicycle axles break gradually. That's why the age-old question of "how
> high of drops can I do?" never makes sense. It's not how high, it's how
> many (x how hard).

Right. I was intentionally vague about what "max stress" I was
talking about. There's yield stress, the force the axle can take
without fracturing. Then there's the elastic limit, the amount of
stress required to permanently bend the axle. Exceed these enough and
the part fails. As you point out, we rarely create enough stress to
cause a new axle to fail in a single event, but, conveniently, the
strength of the part is the same regardless of which of these stresses
you pick as the maximum.

Ken
 
Sofa wrote:
> *
>
> Except for......YOU'RE ON A UNICYCLE!
>
> :) *


Oh, god! Thanks, Sofa. That excuse'll hold for at least a month. Phew!
Until the gras dies and I can see the ground before I land. The thing
that was holding me back was the tall grass all over the rollout making
it so I really couldn't tell if the landing would be any good. Mid-late
summer it all dies, though, and it'll just be more padding for the
landing. Any other excuses that'll assist in my procrastination?


--
gerblefranklin - Trials Unicyclist

Don't you think it's a cruel irony that acting like a G.I. Joe in the
army can get you a Medal, while playing with one can get you thrown out?
------------------------------------------------------------------------
gerblefranklin's Profile: http://www.unicyclist.com/profile/4295
View this thread: http://www.unicyclist.com/thread/31905
 
First of all I'd like to thank Harper for being a guinea pig, testing
these hubs, and sorry the new lame hub failed so early and wrecked your
ride. But I think I've learned something from it.

The first batch of hubs I made had external threads like a Suzue. That
was on purpose because I knew the solid square taper would be stronger
than one with a hole in it. My line of thinking was "why make an
already weak hub weaker by drilling a hole in it?" It's one of those
original hubs that Harper has been riding for almost two years and Ryan
tried to break in Moab.

As we know, there's a problem with the external thread type hubs: it's
tough to keep the cranks on and tight enough. I made a hub with
internal threads to address that problem. I used standard 8mm bicycle
crank fixing bolts and drilled the holes plenty deep to ensure that the
fixing bolts wouldn't bottom out in the hole. I also threaded the hole
deeper than necessary just to make sure the fixing bolt didn't bottom
out in the threads. Now I know that was WRONG!

I'm sure the hole extending beyond (deeper) than the back of the crank
weakened the axle significantly (I calculate about 21% weaker than
solid) and the threads going beyond (deeper) than the back of the crank
only gave the axle a nice place to start cracking internally.

I've come to a conclusion about my making square taper hubs: why
bother?

There's two things to consider when talking about unicycle hubs. One is
material strength and the other is the shape and size of the axle at
it's weakest point. I think the weakest point on a square axle is just
inboard of the crank - exactly where Harper's axle broke. At this point
I measure the square to be .530". On a Profile or KH splined axle this
dimension is almost .750" *round*. The round shape and larger size
makes a huge difference in strength over a square taper. Notice that
"splines" per se don't make a stronger axle ... it's the larger "root
diameter" of a splined axle that makes all the difference.

I've done some calculations and made a drawing showing the result. I'll
stick my neck out here and attach the drawing. I think it *might* be
correct but be aware that I've simplified the forces acting on the axles
to that of simple twisting (not to mention that I probably don't know
what I'm doing!). If nothing else, the drawing shows pretty well what
the relative size difference is between the Profile, KH and square taper
axles. Also, I think I'm conservative on my comparison of the KH to the
Profile because I'm ignoring the eight beefy splines that surely add a
lot of strength to the KH axle.

In conclusion I'll say that Harper's axle broke because the crank fixing
bolt holes were too deep and especially that the threads were too deep.
I don't think the 17-4ph stainless steel was faulty or heat treated
wrong. Actually, I think that G3orge's broken axle is more interesting.
Why did it break inboard of the bearing and in a spot that's greater in
diameter? Perhaps the welded-on flange is to blame?

SH


+----------------------------------------------------------------+
| Attachment filename: spindle ends.jpg |
|Download attachment: http://www.unicyclist.com/attachment/204891|
+----------------------------------------------------------------+

--
showard - ------
------------------------------------------------------------------------
showard's Profile: http://www.unicyclist.com/profile/452
View this thread: http://www.unicyclist.com/thread/31905
 
I'm just glad there are people like you that can do the thinking for
people like me! And I have confidence that someday you'll invent the
"unbreakable" hub/axle/crank combo. Really, very interesting reading,
and nice illustrations Steve:cool:


--
elmer - uniimpaired

"At 40 life begins...to show."
------------------------------------------------------------------------
elmer's Profile: http://www.unicyclist.com/profile/5193
View this thread: http://www.unicyclist.com/thread/31905
 
showard wrote:
> *
>
> I've come to a conclusion about my making square taper hubs: why
> bother?
>
> *
LOL,i got a good chuckle out of that.:D


--
forget_your_life - #3649 plus_your_life

[image:
http://www.unicyclist.com/gallery/albums/albup23/bunnyjumping.gif]
dream one dream many....
*'R.I.P' (http://tinyurl.com/vr86)*
------------------------------------------------------------------------
forget_your_life's Profile: http://www.unicyclist.com/profile/4558
View this thread: http://www.unicyclist.com/thread/31905
 
showard wrote:
> * Actually, I think that G3orge's broken axle is more interesting.
> Why did it break inboard of the bearing and in a spot that's greater
> in diameter? Perhaps the welded-on flange is to blame?
> SH *


one could hazard a guess at "poor technique". however, if you were to
need a test subject for a splined hub, i just happen to have need for a
splined hub. :D in exchange, i'd be happy to send you my broken hub for
analysis.
does the sem wide hub have a welded-on flange?? from the looks o' it,
it looks as if the axle is press-fit into a separate hub piece...
-g3o


--
g3orge - stupid git

happiness is a warm unicycle...
------------------------------------------------------------------------
g3orge's Profile: http://www.unicyclist.com/profile/5477
View this thread: http://www.unicyclist.com/thread/31905
 
"showard" <[email protected]> writes:

> I'm sure the hole extending beyond (deeper) than the back of the crank
> weakened the axle significantly (I calculate about 21% weaker than
> solid) and the threads going beyond (deeper) than the back of the crank
> only gave the axle a nice place to start cracking internally.
....
> I've done some calculations and made a drawing showing the result. I'll
> stick my neck out here and attach the drawing. I think it *might* be
> correct but be aware that I've simplified the forces acting on the axles
> to that of simple twisting (not to mention that I probably don't know
> what I'm doing!). If nothing else, the drawing shows pretty well what
> the relative size difference is between the Profile, KH and square taper
> axles. Also, I think I'm conservative on my comparison of the KH to the
> Profile because I'm ignoring the eight beefy splines that surely add a
> lot of strength to the KH axle.

Thanks for the drawing! I should have done my homework before posting
my estimate. Even so, my calculations end up with different results
than yours: Drilling should weaken the taper by 13%, and the drilled
taper should be only 36% the strength fo the Profiles. If you want,
email me ([email protected]) and we can figure out which of us is
mistaken - I don't want to bore people in the forum figuring this out.

> In conclusion I'll say that Harper's axle broke because the crank fixing
> bolt holes were too deep and especially that the threads were too deep.
> I don't think the 17-4ph stainless steel was faulty or heat treated
> wrong. Actually, I think that G3orge's broken axle is more interesting.
> Why did it break inboard of the bearing and in a spot that's greater in
> diameter? Perhaps the welded-on flange is to blame?

Yep. The weld is my #1 suspect.

Ken
 
On Wed, 21 Apr 2004 01:02:20 -0500, "showard" wrote:

>Notice that
>"splines" per se don't make a stronger axle ... it's the larger "root
>diameter" of a splined axle that makes all the difference.

It's a pity that the ubiquitous square taper design is so small. Were
it twice the size they might be a fine concept also for heavy duty.

Klaas Bil - Newsgroup Addict
--
Clearly a system of 1/14 and 1/16 is not decimal - Mikefule on the English weight system
 
Not that a picnic table drop is anything by the group's standards, but
for what it's worth, whereas the Odyssey cranks were insufficient (both
bent), my Uni.com hardened square taper hub is holding up just fine for
now...but from what I've seen so far, the spines are soon to arrive and
take their rightful place in the center of my wheel.


--
unisk8r - All this for just cross-training?
------------------------------------------------------------------------
unisk8r's Profile: http://www.unicyclist.com/profile/4660
View this thread: http://www.unicyclist.com/thread/31905
 
unisk8r wrote:
> *Not that a picnic table drop is anything by the group's standards,
> but for what it's worth, whereas the Odyssey cranks were insufficient
> (both bent), my Uni.com hardened square taper hub is holding up just
> fine for now...but from what I've seen so far, the spines are soon to
> arrive and take their rightful place in the center of my wheel. *

If you showed up at the 1997 CA Muni Weekend and started jumping off
picnic tables you'd have been in an elite group. Back in the "old" days
that was not the style of riding people were doing. Things are
different now and the equipment has changed to keep up. Back then a
standard unicycle with a 2" knobby tire was a muni. The riding style
was XC with no jumps and drops. Now a basic muni has a fat DH tire,
stronger hub and stronger cranks. Jumps and drops are considered a
normal part of riding.

Back in '98, '99 the Odyssey Black Widow Euro cranks worked just fine
for me. I never worried about them bending. My riding was XC style on
a Pashely MUni and a 2" or 2.1" XC tire. In August of 2000 I bought a
DM Vortex just one month before the 2000 CA Muni Weekend and my riding
style changed.


--
john_childs - Guinness Mojo

john_childs (at) hotmail (dot) com
Gallery: '' (http://www.unicyclist.com/gallery/john_childs)
------------------------------------------------------------------------
john_childs's Profile: http://www.unicyclist.com/profile/449
View this thread: http://www.unicyclist.com/thread/31905
 
You wouldn't happen to still have the frame, would you? If so, would you
ever consider selling it?


--
gerblefranklin - Trials Unicyclist

Don't you think it's a cruel irony that acting like a G.I. Joe in the
army can get you a Medal, while playing with one can get you thrown out?
------------------------------------------------------------------------
gerblefranklin's Profile: http://www.unicyclist.com/profile/4295
View this thread: http://www.unicyclist.com/thread/31905
 
gerblefranklin wrote:
> *You wouldn't happen to still have the frame, would you? If so, would
> you ever consider selling it? *

Which post are you replying to?
If this is about my Vortex muni I've still got it and it's still a
complete unicycle. It's a 26x3. It still gets used, but it doesn't get
ridden as much now that I have a KH 24 because I prefer the 24x3 to the
26x3. The 24x3 is more manageable and maneuverable through technical
bits and the 24x3 is easier to hop with. But when I want to go faster I
use the 26x3 Vortex.


--
john_childs - Guinness Mojo

john_childs (at) hotmail (dot) com
Gallery: '' (http://www.unicyclist.com/gallery/john_childs)
------------------------------------------------------------------------
john_childs's Profile: http://www.unicyclist.com/profile/449
View this thread: http://www.unicyclist.com/thread/31905
 
You must log in or register to reply here.
Top Bottom Back