Choosing butts...

[suhacycles]

Hey y'all,

Was looking at some tube choices for another lugged steel frame project and was wondering, if you had a choice between say thicker wall and shorter butt (say 0.9mm wall and 70mm butt) versus thinner wall and longer butt (0.7mm and 90mm) which would you choose? Assume all else is equal, construction by silver brazing, 28.6 or 31.7 diameter, etc. I take it the choice would also depend if the frame were TIG'd or fillet brazed? I'm pretty sure there wouldn't be a difference in the ride but was wondering what people's experiences were. I also vaguely recall some testing involving hardness of the material along the tube and how it varied depending on silver vs brass construction but don't recall where I saw it... I wanna say e-Richie did those test samples, yes?

-Hansen Su

[Amaro Bikes]

There's no just one answer for your question, as the tube choice depends on too many variables of each frame. The butt sections, for example, would not only depend on if lugged or tig or silver or bronze, it has a lot to say the actual frame geometry so to know how long the actual tube will be and depending on the cut length you'll be able to know how much butted section is left to get the heat. Wall thickness would also depend on the use of the frame (city, road, mtb, etc).
Not to mention the builders skills, thin tube walls with short butts might be calling overheatland, etc. Same goes with hardness of the material, an unskilled builder can ruin the most thick-butted tube with unproper procedures or technique, while a highly skilled one can keep the ultrathin-shortbutted ones within their original specs.

Never think of a tube as an individual, it just belongs to a whole, and the whole has to be consecuent.

Cheers

[Dazza]

and also check, measure, mark the tube to plot where the butt is
One can be trimming both ends of the tube to ensure the butts are deemed sufficient for their location.
I became aware of one builder who despite many years of building was unaware he was mitering Down tubes with the lug edge overlapping onto the butt transition!
I was in the process of securing a new supply of tubing and I was visiting the Milan show later that year, so I was trying to understand what part tube number he was using because it did not make sense to me , I was astonished.

According to my current opinion, it is better to have more length of butt at the head tube ends of the DT and TT then at the BB end and seat tube end.
Measure, mark and cut to fit and know where the butts actually are in the frame you are building.
Regards butt wall thickness and length, I am conservative.

[David Tollefson]

One of the first things I brazed together was a butt gage - a dial indicator mounted to a looong fork. It's surprising how short some of those butts are.

[suhacycles]

I became aware of one builder who despite many years of building was unaware he was mitering Down tubes with the lug edge overlapping onto the butt transition!
I was in the process of securing a new supply of tubing and I was visiting the Milan show later that year, so I was trying to understand what part tube number he was using because it did not make sense to me , I was astonished.

Hey Dazza, I gotta ask, did that builder ever notice any problems down the road with his frames or heard of any complaints from customers relating to that area?

On that note, yeah, I know that a lug edge being say 3 cm away from a butt transition would be less desirable than say 5 cm away. But what if that butt thickness was 0.9 transitioning to 0.6 compared to a longer butt with a 0.7 wall transitioning to 0.5. All else being equal and it was say a DT-HT joint what would you gentlemen pick?

[Dazza]

Hey Dazza, I gotta ask, did that builder ever notice any problems down the road with his frames or heard of any complaints from customers relating to that area?

On that note, yeah, I know that a lug edge being say 3 cm away from a butt transition would be less desirable than say 5 cm away. But what if that butt thickness was 0.9 transitioning to 0.6 compared to a longer butt with a 0.7 wall transitioning to 0.5. All else being equal and it was say a DT-HT joint what would you gentlemen pick?

Every builder I know always claims they never had trouble with failures, so they never admit to any thing
a lot of times this is contrary to the evidence I see with my own eyes.

A lot of people talk of the haze, but I never see problems in the haze area over 35 years, I have only seen it at the TIG weld edge or the lug shoreline edge or where a routing tube was poked through and just brazed into a main tube with out reinforcement.
So I will step up (every one else seems quiet!) and say, ACTMCO (according to my current opinion, with no trade mark)
.9 with 30mm will have a longer fatigue life that .7 with 60mm.
Impact hits, well that might be different.
How it rides, I am not sure you can actually tell if you could compare two frames.

[e-RICHIE]

Hey y'all,

Was looking at some tube choices for another lugged steel frame project and was wondering, if you had a choice between say thicker wall and shorter butt (say 0.9mm wall and 70mm butt) versus thinner wall and longer butt (0.7mm and 90mm) which would you choose? Assume all else is equal, construction by silver brazing, 28.6 or 31.7 diameter, etc. I take it the choice would also depend if the frame were TIG'd or fillet brazed? I'm pretty sure there wouldn't be a difference in the ride but was wondering what people's experiences were. I also vaguely recall some testing involving hardness of the material along the tube and how it varied depending on silver vs brass construction but don't recall where I saw it... I wanna say e-Richie did those test samples, yes?

-Hansen Su

Hansen - Aimar addressed the question well, and it's a hypothetical one at best. So is the answer. If you're concerned, increase the gauge and have it travel longer towards the middle. Just beware, there's a point of diminishing returns thing going on. If you're planning on a lot of impact, curb jumping, or the unforeseen, just be careful with material choices. The brazing, interference fits, and actual quality of the metal you select will also matter. But who's to say how much?!

I'm assuming this frame is for you only, right?

[suhacycles]

Yup, it's for me but since I tend to like things on the slightly stiffer/stronger end I still want it to feel solid under someone who might be 20-30 lbs heavier, especially if one of my friends wants to take it for a spin. FWIW, the tubes I'm looking at are TT Verus HT, Tange Prestige and Columbus Spirit. I was considering some Reynolds 631 to try but I take it the air hardening characteristics really don't mean much if I'm silver brazing, right?

Thanks for the advice gentlemen... until next time!