Integrated seatposts in steel - wall thickness?

[prolix21]

this is an awesomely nerdy discussion, but I'm gonna side with Garro on this one. i've never really understood the need for a non-adjustable seat post outside of really specific race configs.

[Will Neide]

this is an awesomely nerdy discussion, but I'm gonna side with Garro on this one. i've never really understood the need for a non-adjustable seat post outside of really specific race configs.

Just about all of the current iterations of an ISP I've seen have had some range of adjustability. Knowing where my saddle height is on all my frames and what range of movement I personally would need, I would have no problem going with an ISP. I admit that for me it is more aesthetic than function, but hey, we're talking custom bicycles here. Why not get what you want?

[cfrisia]

The ISP is 100% aesthetic in my case.
I didn't expect that the use is so controversial.
But this was not intended to be the point.
(btw.-who in this business is to criticise aesthetic decisions? Why not build all frames without ornamental elements and paint all white? ;) )

Garro, HAZ is in issue of course, but no need to remind me. There are excellent papers/investigations on this.
Same for your engineering criticism - we don't always need to learn by failure and doing things over and over again, this is where we differ from pre-scientific ages.

I just try to approach this with some hard facts, something that I sometimes miss when reading on frame building

Regards

[cfrisia]

This article sheds some light -
Bob Brown Cycles: analysis

scroll down a bit for the Rockwell hardness vs. distance from joint graphs.
A bit on metallurgy - Rockwell hardness and tensile strength are almost proportional in heat treatable steel (eg Chrome/Moly alloys, microalloys etc.).
That means, if the hardness drops to 82% (as in the ishiwata for example), tensile strength does too.
Keep in mind, this is the maximum drop. A positive prospect, isn't it?

back to my issue, the ISP would not bend, it would buckle. As also shown by Mark, the buckling resistance is not dependent on actual tensile strength.
It is determined by modulus of elasticity and radius vs. wall thickness.
Strictly spoken, even if the tensile strength would drop by 50%, the ISP is more likely to fail because of its dimensions rather than because of its strength.
(This is just a ballpark figure, maybe the heat required to drop the strength by 50% would totally destroy the brazing alloy or induce microscopic crystal structure faults etc)

Of course one needs to braze it properly, and I'm able to do so (please don't get me wrong in the post above - I'm not trying to say "there are investigations, no need to learn heat control" - this is not how all engineers think ).

regards

[Mark Kelly]

this is an awesomely nerdy discussion, but I'm gonna side with Garro on this one. i've never really understood the need for a non-adjustable seat post outside of really specific race configs.

So I'm a nerd. Deal with it.

The frame I built myself last year would have had an ISP if that didn't make it too big to fit in a Qantas box for my trip to Tasmania (80cm max height). My saddle height hasn't changed in thirty years and I keep my bikes so I can't see the problem with ISPs myself.

[steve garro]

I didn't expect that the use is so controversial.

Garro, HAZ is in issue of course, but no need to remind me. There are excellent papers/investigations on this.
Same for your engineering criticism - we don't always need to learn by failure and doing things over and over again, this is where we differ from pre-scientific ages.

I just try to approach this with some hard facts, something that I sometimes miss when reading on frame building

Regards

1st, I don't care how you build it, I do hope you do it safe.

2nd - dude, you've got it 100% backwards, and I fucking hate this about the internet and framebuilding - YOU ARE THE ONE ASKING HOW TO DO IT SAFELY AND WHEN CONFRONTED WITH AWNSERS YOU DON'T LIKE YOU GET ALL PISSY. i EXPECT THE WORD "HATER" TO BE THROWN OUT SOON.

3: IF YOU DON'T LEARN FROM THINGS FAILING OVER & OVER AGAIN, WHAT DO YOU LEARN FROM?

4: I HOLD THAT YOU HAVE ZERO HARD FACTS - YOU HAVE #'S

Man..........I'm starting to sound like Dazza.
I'm stoked on that.
I only jump in anymore to try to save people who I think are doing sketchy things, and that might make me sound like a curmudgeon, but if people seem to "have it down" then why chime in at all?



Good luck, really.
- Garro.

[Will Neide]

3: IF YOU DON'T LEARN FROM THINGS FAILING OVER & OVER AGAIN, WHAT DO YOU LEARN FROM?

I think he's just saying he wants to do this in a scientifically controlled way with numbers to support his assertions. My impression is that he's just kind of looking for real world buliders opinions to support what his math says. I don't think his goal is to fail at all, but start with a solidly safe, yet minimal, starting point. I'm sure if it does fail he will learn from it, but since he apparently has never built one, then he's hoping not to fail on his first attempt. IMO. Bricoleur vs Engineer?
:)

[cfrisia]

woa woa Garro, I didn't mean it like that. English isn't my first language, it probably came out wrong.

I'm not pissy - there's been input from bellman/jake about using a 0.8 thickness instead of 0.6. after some input by Mark pointing out that my assumptions for dimension were faulty, I wrote that I'll take 0.8 because it compares well to aluminum posts in terms of buckling resistance.

I just tried to say that I am aware that proper brazing is important but not the vital issue for me.

Of course I want to do it safely, but I don't see why I should overdimension it. We had some calculations here, but the stresses in a seatpost are not completely tangible, so I sought for real life experiences. Otherwise I wouldn't have needed to discuss and could've taken a really thick gauge.

I learn from planning, investigating and doing. I make mistakes, but I can greatly reduce their number by emphasizing on the first two parts.

Please accept my apologies, I did not intend to make your angry. Please know that a lot of stuff you posted here and on the old framebuilding forum was a big help to me when I started.

[steve garro]

I think he's just saying he wants to do this in a scientifically controlled way with numbers to support his assertions. My impression is that he's just kind of looking for real world buliders opinions to support what his math says. I don't think his goal is to fail at all, but start with a solidly safe, yet minimal, starting point. I'm sure if it does fail he will learn from it, but since he apparently has never built one, then he's hoping not to fail on his first attempt. IMO. Bricoleur vs Engineer?
:)

“An expert is a man who has made all the mistakes which can be made, in a narrow field.”
Niels Bohr

I'm not trying to piss in anyone's wheaties.
Just trying to keep someone from a forced 4130 anal probe.
What ever happened to building in a margin of safety & working backwards from there?
Nobody's goal is to fail, is it?
It's not like 1.125" x .035" is heavy..........!
- Garro.

[steve garro]

I did not intend to make your angry.

You haven't - frustrated, maybe.
I appreciate what you are trying to do.
Just maybe start off with a good margin of safety built in, yeah?

As we all know, ultimately all engineering disasters can be traced to a lack of redundancy, right?
Maybe bond in a CF or Al sleeve in the highest stress area?
- Garro.

[cfrisia]

Good to hear that. I have to learn more modesty.

I thought about making the whole thing from cf and glue it in, similar to what I saw from Ritte.
An all-steel design is seductive nevertheless :)

[anon.]

Just out of curiosity, why are you married to the idea of a 28.6 st? Going to a larger tube ID would give you the ability to use a cap-style topper rather than a stub post.

[Mark Kelly]

Just out of curiosity, why are you married to the idea of a 28.6 st? Going to a larger tube ID would give you the ability to use a cap-style topper rather than a stub post.

Going to a larger tube diameter exacerbates the buckling issue due to decreased t/R - inversely proportional to diameter for equal thickness, inversely proportional to the square of diameter for equal weight. (31.8 / 28.6)^2 ~ 1.25.

[cfrisia]

Yes, because it'd become heavier but also because it looks a tad too big for my taste.
The frame will have a 36mm ht, 31.7 dt, 28.6 tt.

Regards

[Amaro Bikes]

I do like isp as an aesthetic thing, and I kind of thought at the beginning all those old cumugdeons framebuilders were always being discouragin people and the like.

Boy, how wrong I was! Even if didn't have to go through a broken isp, I can't think of anything as valuable of those experienced guys sharing their incredibly valuable knowledge with no more interest than helping newcomers to avoid fatal mistakes (although I do also think nothing gets better learned than experienced by yourself). I guess we would never be thankful enough for their open doors attitude.

Regards

[liberacefanboy]

omg.
here it is:
DO NOT DO IT.
I am one of the " because I can " builder guys, but seatmasts like this are crazy. they will fail.
I dont care about wha tthe " science and numbers " say. Real life is way worse than science and numbers.
It is one of three things I will not build, no matter what money is thrown at me.
PLEASE don't do this. Its the best advice I can give you when you came here to the Salon.
Take this from a guy who just got nine, yes 9 stitches in his ass. Not seatmast related, but it could have the same if not worse effect it that thing broke.
noren

[Will Neide]

omg.
here it is:
DO NOT DO IT.
I am one of the " because I can " builder guys, but seatmasts like this are crazy. they will fail.
I dont care about wha tthe " science and numbers " say. Real life is way worse than science and numbers.
It is one of three things I will not build, no matter what money is thrown at me.
PLEASE don't do this. Its the best advice I can give you when you came here to the Salon.
Take this from a guy who just got nine, yes 9 stitches in his ass. Not seatmast related, but it could have the same if not worse effect it that thing broke.
noren

My wife just a stitch or two down there as well, but she just had a baby last weekend. For some reason the first time she had a baby she got stitches then too, but this didn't seem to stop the inevitable from happening.

[steve garro]

My wife just a stitch or two down there as well, but she just had a baby last weekend. For some reason the first time she had a baby she got stitches then too, but this didn't seem to stop the inevitable from happening.

I honestly don't know why we try sometimes.
this place used to have some great builders who went away because they quit caring.
Good Luck - may be your last child with the ISP experiment.
- Garro.

[Will Neide]

“An expert is a man who has made all the mistakes which can be made, in a narrow field.”
Niels Bohr


It's not like 1.125" x .035" is heavy..........!
- Garro.

I honestly don't know why we try sometimes.
this place used to have some great builders who went away because they quit caring.
Good Luck - may be your last child with the ISP experiment.
- Garro.

Stealing your quote, I think it's only fair that tinkerers will not easily be thwarted, and probably isn't best to tell them "DON'T DO IT because it will fail!" We've all seen an ISP done on some bikes and they clearly haven't failed. Many reputable builders can solidly build one. The question the freelance tinkerer has is, "Why did that one work and not that one?" It's not a matter of telling them "Don't do it!," but how about a little guidance to minimize errors. How are people to become experts if you won't let them make mistakes? I take it as a forgone conclusion that no matter what anyone in this thread thinks, Cfrisia is going to build what he wants. He just needs guidance (and I benefit from the suggestions of tubing as well since at some point in my life I wouldn't mind tackling this same project.)

Great builders come and great builders go. Maybe Cfrisia is the next great builder? Who the heck knows.

And it may be the last child anyway. 3 may be my max. :)

[liberacefanboy]

Seatposts are designed to flex a little bit.
I and Garro are telling you dont do it, because the one that breaks will be the one YOU pay for. Like as in if you get sued.
Its just not a good idea, and Thomson makes a hell of a seatpost. You wanna talk fluff, seatmasts are fluff. What is it adding to the bike? how does it make it better?
Last I have to say about it, judt don't. Save the Advil for me.
noren