seat stay "helenic" style

[Rui Rodrigues]

Hi,

I am a newbie in framebuilding (2 frames fillet braze) and preparing my next project. This is my first post but I am a long term reader of the group. Thanks to all of you to share so much of your experiences and skills as  this allows others (like me) to engage into the great and painful adventure of building ;)

For pure aestetics reasons (bad I know), I want to build a frame with "helenic" seat stay. JP Weigle has just finished one for the last cirque and I can't sleep since :)

I am completly in love with this design and would like to try reproduce it.

My newbie questions (not criticising Mr Weigle works's, just trying to understand his work.)

Why is the seat tube sleeve so short (not going all the way down to the SS junction)? As a newbie I am scared to overheat the area (ST-SS) and deform the seat tube which is quite thin in this area (0.6mm). Or I am worrying about nothing.

The bike built by Jo Routens don't look like there is any sleeve around the seat tube: Why is that? Thicker seat tube and smaller seat post?

Thanks for your help. Have a great day,

Rui.

[Andrew R Stewart]

Rui- I'll try to give some answers, although more experienced builders might have greater insight then I. I only built about 5 Helenic frames many years ago and I was pretty  wet behind my ears then.

 

The reason to not have a sleeve extend further down the ST and act as a thicker contact point for the seat stays crossing on to the TT is that with good heat control one doesn't need it. the stresses the ST/SS contact patch sees is less the if the stays ended at the ST. As they extend past and solidly attach the the TT the small, and likely silvered, contact with the ST is sufficient. With good temp control little if any distortion will be present on the ST and after brazing reaming will remove minimal material.

 

Not asked but an aesthetics question is the size of the "triple triangle" (as the brand GT called it). JP Weigle chose to have the stays attach to the TT on it's sides. This pretty much requires the attachment point to be far back on the TT./ If the ST is slightly larger in diameter then the TT is (say, 1.125" ST and 1" TT) then the angle the stays have coming off the drop outs will define the locations of the two contact points (the ST and the TT), unless some other method is used to deal with those contact points.

 

At Cyclery North we liked the SS to just touch the ST side  and butt onto the TT underside (like a fastback cluster). This meant that the SS was angled further down and crossed the ST lower down. It was a bit of a jiggle to make all the contact points happy and also look nice. On big frames the 'triple triangle" tended to be small and on small frames it was larger. This made the aesthetic less balanced. How the SS angle compared to the DT angle and how the "triple triangle" compared to the main triangle were the driving issues.

 

How the top ends of the SS blended together and also cupped the underside of the TT was one way we managed the issues and dimensions. Sometimes we had the top of the SS slightly overlap the TT on it's side, the SS wall would extend just past the TT's side and get curved around the top of the TT. Sometimes we blended the two ends of the SSs before they butted onto the TT, there were the hardest style for me to miter. Sometimes we wanted a SS top look that made the contact point with the ST not exist, there would be a small gap. We would add a tiny cross piece of small diameter rod or tube and fillet enough to hide that there was a connecting element that wasn't just a large fillet joint. The classiest that Tommy (the other and far better builder at CN) did was to use a ball bearing held in place with small holes drilled in the SS and ST. Then using a small fillet this connecting element had it's own set of curves. Watching Tommy position the holes was a study in focus.   

 

https://www.flickr.com/photos/73195587@N00/3347325999/in/set-72157615123048864/

 

https://www.flickr.com/photos/73195587@N00/3342408495/in/set-72157614977063963

 

Here are two links to check out. The first is of a bike Tommy made but doesn't show much detail except the overall proportioning of the frame. The second is one shot within my album of some of the frames I built during my 7 months at Cyclery North. There are shots with better details of the Helenic treatments, you'll have to poke around within the album to view all the shots. Feel free to check out other albums of frames I've done as well. While I never did more Helenics there are some interesting little details scattered among my frames. Also I always like looking at the shops, tooling that other builders have. I've had the fortune to build with a number of other builders, and their shops, as well as have to move my shop many times. You'll see the progression of my set ups.

 

Their are some really nice Helenics done out there to try to duplicate, steal ideas from. But there are also some really clumsy looking ones to avoid. Have fun with your research and next building project. Please post photos when you're done. Andy.

 

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Andrew R Stewart
Rochester, NY

[Jon Norstog]

Rui,

Peter can do things with a torch that the rest of us probably should not try.  I would definitely sleeve the seat tube at the stay joint.  You also may have a difficult miter where the stays join the top tube.  Take your time and good luck!

jn

"Thursday"

[Rui Rodrigues]

Hi guys, thanks for your feedback.

I was also thinking about a longer sleeve until I read a post from Mark Bulgier who advise against brazing a long sleeve on a tube. In my case the sleeve would be like 50 or 60mm long...is it too long?...

also, shall i go for a reinforcement on the top tube? (I am thinking silver brazing the SS on the TT so stress would be minimal. I don't think distortion is a problem in that area).

cheers,

Rui

[M-gineering]

If you're building lugless just get an externaly butted seat tube

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mvg

Marten Gerritsen
Kiel Windeweer
Netherlands

[Mark Bulgier]

Rui Rodrigues wrote:

I was also thinking about a longer sleeve until I read a post from Mark Bulgier who advise against brazing a long sleeve on a tube. In my case the sleeve would be like 50 or 60mm long...is it too long?...

 

A bit off topic from your original question, but I’ll tackle that.  A doubler that long can be done, but I just don’t like it.  Maybe my reasons aren’t so important to you. 

 

It’s not easy to get filler to penetrate over that long distance.  Even if you feed it all in on one end and have it come out on the other end, you don’t know if you have full penetration. Voids in the joint, with maybe flux or maybe just air in them, might not cause problems (probably won’t, I’ll bet), but I just don’t like not knowing.  Plus that’s more heat and duration (time at temperature) than needed.   And then you re-melt the filler inside the sleeve when you braze the top tube on (and TIG welding the top tube is not an option at all, with brazing filler underneath). But short of the TIG exception, it’s unlikely to cause your frame to fail, unless you really cook it.  So don’t consider this a rule, more of a preference.

 

Marten’s idea of an externally-butted seat tube is an excellent one, or you can use an internally butted tube, a.k.a. downtube as a seat tube.

 

If you must use a single-butted light-weight seat tube, then it should be reinforced at the top.   If a longish reinforcement suitable for fillet brazing or welding the top tube is needed, the style I like is more work and requires a lathe.  I’ve described it before on this list but it’s nothing special, just a piece of 1-1/4” x .095 4130 bored in a bit from one end to fit the seat tube, and turned down to a reasonable OD. I made the socket depth pretty much the bare minimum except with nice-looking lug points front/back.  Very quick/easy to braze the tube into the socket.  The entire portion where the TT is welded or brazed on is in the solid section fully above where the seat tube is brazed in its socket, so no remelting. 

 

Maybe you can buy these pre-made? I think Ritchey used to sell a piece pretty much like mine but plain cut at the bottom, no lug points.  Maybe they still do or someone else (Nova, Ceeway?) does.

 

But first let me say, on the original question of a “Hellenic”, why not do a small reinforcement at the top for the seatpost pinch bolt and/or top tube (can be a normal commercially available seat lug), and then another even smaller one down where the stays cross? Or two smaller diamond or four-pointed star reinforcements, one at each seatstay – they don’t even have to meet up with the diamond on the other stay. Even a small diamond will spread the stress out over a larger area of seat tube.

 

Mark Bulgier

Seattle

 

[Rui Rodrigues]

Thanks for your feeedback.

the externally butted ST seems the way to go! Time to start :)

Rui

[Duane Draper]

Ceeway sells a rough pre-made sleeve that I had good luck with.  It's not as long as you are proposing though.  Perhaps Mark or other experts could comment on side reinforcement plates at the ST/SS brazing point.  If it was done with brass and then the seatstays were done with Silver, that seems like it could work and add some nice interesting detail?  I have read elsewhere that gussets can cause more problems than they solve if not done correctly but, perhaps this is a low enough stress area to get away with it?