seatstay taper and wall thickness?

[Ant]

Are seat and chain stays tapered on modern welded bikes becuase of function or for aesthetic
reasons? I am going to build a frame from aircraft chromo (many thanks to those who pointed me in
the right direction) and am wondering

1. if there is any functional reason to the taper (older bikes dont have tapered stays, but maybe
they didnt know something?)

2. waht an appropriate wall thickness would be for the seat/chain stays. For the main tubing, im
using a straight gaube tubeset that works out to about .85 mm. but what to use for the stays?
options range from .71 mm up. id like to go light, but with this metal and construction, is that
too thin, or just fine?

thanks to all for your continued excellent advice, anthony

 

[John Retchford]

"ant" <[email protected]> wrote in message
news[email protected]...
> Are seat and chain stays tapered on modern welded bikes becuase of function or for aesthetic
> reasons? I am going to build a frame from aircraft chromo (many thanks to those who pointed me in
> the right direction) and am wondering
>
> thanks to all for your continued excellent advice, anthony
>
Anthony,

I read your previous post and the answers of others. I would think carefully about this project or
yours - I think you are on the wrong track. For most of us, building a good, accurate, properly
aligned frame by hand requires a fair amount of work and thought - probably more than you realize
now. When I have put in that work I wanted a good frame at the end of it, one that I could be proud
of and that suited my needs. I built my "ideal" light touring frame about 10 years ago. Building it
was interesting and satisfying (and hard work) but not nearly as satifying as riding the 100,000 km
since, in 8 countries. I don't think it would have been nearly as satisfying had it been made from
bits of straight aircraft tubing.

So my advice is this: If you want to improve your welding of brazing, make test pieces or go to
classes. If you want a good bicyle frame, use bicycle tubing. In all but the most exotic steels,
bicycle tubes are not unduly expensive and they are sized for the stresses involved, have
round-oval-round chain stays, tapered seat stays and wonderful fork baldes. Bicycle tubing makers
pioneered some very ingenious techniques for making tubing. Why not make use of this? They probably
cost a little more, but the differential will be a small part of the total cost and who builds
custom bicycles to save money?

John Retchford

 

[John Retchford]

"ant" <[email protected]> wrote in message
news[email protected]...
> Are seat and chain stays tapered on modern welded bikes becuase of function or for aesthetic
> reasons? I am going to build a frame from aircraft chromo (many thanks to those who pointed me in
> the right direction) and am wondering
>
> 1. if there is any functional reason to the taper (older bikes dont have tapered stays, but maybe
> they didnt know something?)
>
> 2. waht an appropriate wall thickness would be for the seat/chain stays. For the main tubing, im
> using a straight gaube tubeset that works out to about .85 mm. but what to use for the stays?
> options range from .71 mm up. id like to go light, but with this metal and construction, is
> that too thin, or just fine?
>

Anthony,

I read your previous post and the answers of others. I would think carefully about this project or
yours - I think you are on the wrong track. For most of us, building a good, accurate, properly
aligned frame by hand requires a fair amount of work and thought - probably more than you realize
now. When I have put in that work I wanted a good frame at the end of it, one that I could be proud
of and that suited my needs. I built my "ideal" light touring frame about 10 years ago. Building it
was interesting and satisfying (and hard work) but not nearly as satisfying as riding the 100,000 km
since, in 8 countries. I don't think it would have been nearly as satisfying had it been made from
bits of straight aircraft tubing.

So my advice is this: If you want to improve your welding of brazing, make test pieces or go to
classes. If you want a good bicycle frame, use bicycle tubing. In all but the most exotic steels,
bicycle tubes are not unduly expensive and they are sized for the stresses involved, have
round-oval-round chain stays, tapered seat stays and wonderful fork blades. Bicycle tubing makers
pioneered some very ingenious techniques for making tubing. Why not make use of this? They probably
cost a little more, but the differential will be a small part of the total cost and who builds
custom bicycles to save money?

John Retchford

 

[Ed Ness]

"John Retchford" <[email protected]> wrote in message
news:<[email protected]>...

> Anthony,
>
> I read your previous post and the answers of others. I would think carefully about this project or
> yours - I think you are on the wrong track. For most of us, building a good, accurate, properly
> aligned frame by hand requires a fair amount of work and thought - probably more than you realize
> now. When I have put in that work I wanted a good frame at the end of it, one that I could be
> proud of and that suited my needs. I built my "ideal" light touring frame about 10 years ago.
> Building it was interesting and satisfying (and hard work) but not nearly as satisfying as riding
> the 100,000 km since, in 8 countries. I don't think it would have been nearly as satisfying had it
> been made from bits of straight aircraft tubing.
>
> So my advice is this: If you want to improve your welding of brazing, make test pieces or go to
> classes. If you want a good bicycle frame, use bicycle tubing. In all but the most exotic steels,
> bicycle tubes are not unduly expensive and they are sized for the stresses involved, have
> round-oval-round chain stays, tapered seat stays and wonderful fork blades. Bicycle tubing makers
> pioneered some very ingenious techniques for making tubing. Why not make use of this? They
> probably cost a little more, but the differential will be a small part of the total cost and who
> builds custom bicycles to save money?
>
> John Retchford

I couldn't agree more with this advice. Spend the money and buy the real stuff. Joe Bringheli at
www.bringheli.com will sell you a complete tubeset for less than $50 so to cheap out further is
pure folly.

Another thing to consider is to post a "wanted to buy" message on the framebuilders list. No doubt
someone has a few spare tubes they will sell you for cheap. In fact, I have some if you want to drop
me an email.

Good luck.

Ed

 

[Bluto]

ant <[email protected]> wrote:

> 1. if there is any functional reason to the taper (older bikes dont have tapered stays, but maybe
> they didnt know something?)

Tapered tubes distribute stresses along greater lengths than straight tubes, which tend to
concentrate stresses next to joints.

Tapered stays in this way serve an analogous function to butted main tubes.

> 2. waht an appropriate wall thickness would be for the seat/chain stays. For the main tubing, im
> using a straight gaube tubeset that works out to about .85 mm. but what to use for the stays?
> options range from .71 mm up. id like to go light, but with this metal and construction, is
> that too thin, or just fine?

My impression is that sub-1mm walls are going to be flimsy unless the tubing is oversized. If you
have a resource of junk frames you can dissect, I'd cut up and measure one made of straight gauge
4130 CrMo to get a baseline from which to vary.

It's probably easiest, as a previous poster said, to just use a bike tubeset if you are building a
normal bike in a normal size. Much design refinement will have been done for you if you choose a
stock tubeset. As a novice, you should use as forgivingly thick-walled a tubeset as you can buy. If
fabricating with thin-walled tubing were easy, you'd be able to get a custom frame at any auto
chassis shop.

Since bike tubesets are made in stupidly narrow size ranges, however, you should ignore such advice
if your design is very differently proportioned than average.

Be generous with tube wall thickness, though. You can always build a lighter one as your skills
improve, but it would be a disappointment to struggle with finicky thin tubing only to have your
frame fail structurally because you overcooked it.

My first custom frame used 1.5"x.035" top and down tubes, 1"x.058" seat tube, and .75"x.049" stays.
Built for a friend of mine, it's been in service eight years now as regular transportation. He's
happy with it and so am I.

Chalo Colina

 

[Ant]

"John Retchford" <[email protected]> wrote in message
>
> I read your previous post and the answers of others. I would think carefully about this project or
> yours - I think you are on the wrong track.

John and others- thanks for your advice. As luck would have it, I made two breakthroughs in my
fledgling framebuilding career (actually *hobby* re: a current thread on the frame list) this week.
first, i forced my computer to finally recognize the bikelist.org server with the help of a savvy
networking pro. the framebuilding list has already been a great help. second, i learned that
bringheli is selling off his low end dedacciai zero tre tubeset for cheap, and i bought a set for 42
dollars shipped. nine tubes. this is so low that it approaches or matches aircraft 4130 prices, so i
couldnt resist.

i have to say- every step of the way i get strong advice much like that you are giving me. It is
generally either 'use the right materials, you wont regret it', or 'buy the book, you wont regret
it'. both of these are obviously true, and im doing my best. for the time being, i spend an
inordinate amount of time welding small pieces of scrap metal together, and the little remaining
time pouring bike info on the web into my head.

best news of all? i convinced my college to give me class credit to make a couple frames this
semester. hows that for a liberal arts education?

thanks for your collective help, with this and all my other questions.

anthony