Seatpost Design Discussion for Engineers

[Minion]

 

 

On a different subject' date=' when you crash and that crash causes metal fatigue, is this the manufacturers fault ?

 

[/quote']

A crash can't cause metal fatigue (unless you happen to crash really often). Fatigue is caused by repeated loading/unloading cycles that result in the formation and growth of cracks.

A crash might cause the post to break at a pre-existing fatigue crack, but it should be fairly simple to determine if this was the case as fatigue cracks are quite distinctive.

 

Edit: If you've got some pics of a 350x31.6 Elite setback seatpost, post them here and I can take similar pics of a Masterpiece for comparison.

Edman2009-04-17 06:52:33

[SwissVan]

Can't say I have....  I make a mean lasagna though

 

 

 

hmm well i was hoping we could say you were a cullinary engineer.

 

Lasagna engineer wont pass JB's scrutiny. 

 

 

[Nancy Drew]

I make a mean lasagna though]

What is your secret? I make my own pasta and want to try that soon.

 

dude.. if I told you, it wouldn't be my secret

 

 

[AndreZA]

dude.. if I told you' date=' it wouldn't be my secret[/quote']

 

 

 

if you PM me it can be our secret.

[splat]

How thick are the rails on a Fizik Gobi?

How many saddles have 7mm rails? Is that the standard' date=' or is 7 thicker than most?

 

[/quote']

 

Sorry to interupt your lasagne engineering thread, but does anyone know much about this?

[Wyatt Earp]

Splat

 

 

 

7 mm's is pretty much the standard.

[Wyatt Earp]

 

 

 

On a different subject' date=' when you crash and that crash causes metal fatigue, is this the manufacturers fault ?

 

[/quote']A crash can't cause metal fatigue (unless you happen to crash really often). Fatigue is caused by repeated loading/unloading cycles that result in the formation and growth of cracks.A crash might cause the post to break at a pre-existing fatigue crack, but it should be fairly simple to determine if this was the case as fatigue cracks are quite distinctive.Edit: If you've got some pics of a 350x31.6 Elite setback seatpost, post them here and I can take similar pics of a Masterpiece for comparison.

 

Cool beans Edman will do.

 

 

 

 

[Nancy Drew]

Can't say I have....  I make a mean lasagna though

 

 

 

hmm well i was hoping we could say you were a cullinary engineer.

 

Lasagna engineer wont pass JB's scrutiny. 

 

 

 

I have an A+ diploma which means I can pretend to know some technical stuff about PC's?  I'm pretty good with Excel? I work with a lot of engineers (I think I'm cleverer than some of them)...... dunno, you're gonna have to help me out here with a title that will pass the scrutiny of Mr Bornman

 

 

 

 

[Nancy Drew]

dude.. if I told you' date=' it wouldn't be my secret[/quote']

if you PM me it can be our secret.

 

Hmmm..... it has to do with bacon and red wine.... and like a good stew, tastes much better the next day.

 

I'll think about it

 

 

[Wyatt Earp]

OK Edman

 

 

 

I am guessing and speculating that the post in question has been crashed with numerous times, which is what I said at the start of my discussions.

 

The dude is not too forthcoming as to what really happened and that is why we can't just make a statement as the one which was made in the starter post.

 

 

 

Here are the pictures as requested sir, please bear in mind that this is from my old 3 MP camera

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sorry for the edit, Edman, in your professional opinion do think the Thomson design could possibly suffer from a "pre-existing fatigue crack" as you said.

 

I am very surprised at the failure involving the discussed post, I have never seen a Thomson post break, crack or whatever one could imagine.

 

I feel that there is either foul play or just something out of the ordinary regarding the failed post.Summit Cycles2009-04-17 07:30:41

[Johan Bornman]

A design cannot suffer from a "pre-existing fatigue crack".

A pre-existing fatigue crack is a crack that developed from extended usage.  It is a crack that's been developing over time - hence the pre-existing bit. A crash is usually the final straw that breaks the camel's back.

Spokes break like that. A fatigue crack starts and travels through the spoke until the last remaining piece cannot take the strain anymore and gives way. The last little tip breaks in tension whereas the rest breaks through a traveling stress crack.

 

It is quite easy to see fatigue cracks. The metal displays a course crystallisation with lines that indicate the direction of crack travel. The bit that broke under tension displays a smoother surface than the rest and pulls to a point.

 

 

[Dirtbreath]

For the sake of reference I attach the photo of the damaged post:

 

 

Something has been bugging me and after pulling my post out I now know what it is. The top face of the ear is actually level with the top of the seatpost body. How on earth did the ear shear off here? Impossible. The top face would be black anodised. Something is amiss here.

 

 

[Wyatt Earp]

JB

 

Hence my question, I get the feeling Edman was suggesting something else or might have a different explanation/meaning.

 

I am quite keen to hear his opinion, I am still very surprised to see this happen to a Thomson post.

 

 

 

Dirtbreath, I am leaning more towards a few crashes and over tightening of a bolt.Summit Cycles2009-04-17 08:56:25

[Minion]

 

JB

 

Hence my question' date=' I get the feeling Edman was suggesting something else or might have a different explanation/meaning.

 

I am quite keen to hear his opinion, I am still very surprised to see this happen to a Thomson post. .[/quote']

I was just commenting that fatigue is a (relatively) long, cumulative process, not a single event failure.

I wasn't able to read the linked post properly at work, but I'm doing so now. Stay tuned.

 

[Minion]

Also, just to note that Thomson do claim they performed fatigue tests on their seat posts:

Over double the fatigue life of any other

production models we tested.

- from their site

[Wyatt Earp]

Thanks Ed

 

 

 

I will join you chaps later, I am of to install a new review sample have some work to do.......

 

 

 

Review sample: