Understanding the limits of tubes and braze-ons

[frankbike]

Hello folks,
I'm starting a framebuilding activity un Brussels, Belgium and while I'm quite confident with the quality of my work, I lack the background and experience to fully appreciate the (possible) limitations inherent in the tubes and braze-ons available on the market. Here are a few concrete situations in which I'm looking for guidance:

1. What diameters and ranges of tubes are best for a fairly tall, heavy rider (1m90/100kg(220lb))?
2. What diameters and ranges of tubes for more demanding activities such as mountain biking?
3. Is it realistic to install a child's seat on a rear rack with pannier bosses brazed on the SS or is this just too much weight ?
4. In general, are there hard limits in terms of usage you feel a handmade steel brazed bicycle shouldn't approach ?

At this stage, I'd like to use only tubes that are ‘easy’ to work with, such as Columbus Zona tubes and brass brazing as joining process.

Thanks for your feedback.

François

[e-RICHIE]

Mine may likely be an unpopular reply to your question.

I'm of the mind that materials take a back seat to experience, and without the the latter, the former - even more of it (thicker, wider, etc.) - won't help you solve the problem.

Are you making lots of frames? Are the tools available to you lacking in any way? I'm not advocating for lightweight or thin wall tubing here. I'm also suggesting that beefing up won't mask a lack of skills.

Let us know some background. That would help the conversation along. And PS welcome to the room.

[frankbike]

Hello Richard,
Thanks for your reply and welcoming :)

I've built 6 frames so far. I'm certainly not experienced, but the purpose of this question was to try and understand the intrinsic limits of the materials we use (if any).

Of course, I understand that the framebuilder's talent goes a long way, but aren't there rules-of-thumb in the choice of tubes (diameter, families) depending on the scenarios presented?

Is bronze brazing sufficiently solid (if well executed) to withstand the impact of a 15kg child seat?
Won't a tall rider have problems with frame rigidity (or weakness) if the diameter of the tubing is too thin?

If the answer is no, and it all depends on the craftsman, that's fine by me too :)

[Andrew R Stewart]

Hello Richard,
Thanks for your reply and welcoming :)

I've built 6 frames so far. I'm certainly not experienced, but the purpose of this question was to try and understand the intrinsic limits of the materials we use (if any).

Of course, I understand that the framebuilder's talent goes a long way, but aren't there rules-of-thumb in the choice of tubes (diameter, families) depending on the scenarios presented? yes and no, as people will sway from following what others have done before to what no one does (that they know of at least:). A quick look through a few bike brand spec sheets will show the middle of the generally accepted bell curve.

Is bronze brazing sufficiently solid (if well executed) to withstand the impact of a 15kg child seat? Sure, but design has a lot to do with things like leverages and bracing angles, of course this is where some skill counts.
Won't a tall rider have problems with frame rigidity (or weakness) if the diameter of the tubing is too thin? Maybe. Tube stiffness is more a diameter controlled thing than a wall thickness one. if the tubes were too thin I'd be concerned about brazing skills and what the expected lifespan of the frame is understood to be. Not the ride quality anywhere as much.

If the answer is no, and it all depends on the craftsman, that's fine by me too :)

So by my view both skills and materials are in play but I'd rather own a well built frame made from basic grade tubing than a poorly made one from a wonder tube set.

Has the OP done any destruction tests of their work? Any repairs of other's work? Made any mistakes yet? Andy

[e-RICHIE]

<snipped>

If the answer is no, and it all depends on the craftsman, that's fine by me too :)

I believe experience trumps technology. And I’m aware that it’s an abstract thought. No amount of beefing up the structure will be a buffer against workmanship or the assembly skills of the under or untrained.

On the other side, if you’ve made the six aforementioned frames and are sure they’ll stay together over the long haul, you’re already ahead of the curve.

Before you assembled these six, what experiences did you have to know what went where, or why? My ask is to get a better understanding re the kind of advice that’d help you the most.

[steve garro]

Look at proven designs around you and practice brazing a lot

- Garro.

[frankbike]

Thanks for all your inputs !
I guess my question was more related to the material sold by modern manufacturers (Columbus, Reynolds and Dedda) and the fact that they all offer very optimized tubing profiles with the thinest wall thickness possible, butting, ... And hence, I'm wondering if we can still pretend to to all kind of bikes with those or if there are areas (for instance downhill bikes, heavy duty bikes) that cannot (or should not) be built using these :)

[Paul Jacobs]

This book is 35 years old but the discussions of steel tubing profiles and thickness in relation to designing frames for different purposes are still relevant. Used copies are readily available.

[claritycycler]

^^^

This book is 35 years old but the discussions of steel tubing profiles and thickness in relation to designing frames for different purposes are still relevant. Used copies are readily available.

Interesting, and popular as a google search indicates most used copies are around $70 but I did find one for $40. I'd like to read it but think I'll check local libraries on the unlikely chance they have it.

link to article on steel tube thickness and diameter, a little dated but imo pretty good
https://valvejob.wordpress.com/2016/...all-thickness/

and
https://valvejob.wordpress.com/2020/...al-compliance/

[steve garro]

And hence, I'm wondering if we can still pretend to to all kind of bikes with those or if there are areas (for instance downhill bikes, heavy duty bikes) that cannot (or should not) be built using these :)

What does your intuition and experience tell you?
if you are selling bikes you should be able to design one without internet help


- Garro.

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