Fillet brazed head tube
 

I'm planning to fillet braze a road frame. I have a Columbus SL tubeset with a head tube suited for 1" steerer. The wall thickness is 1mm.
I've read in "The Paterek Manual" that standard head tubes are designed for lugs and are not strong enough for fillet brazing. I've also read from other sources that the head tube should be reinforced for fillet brazing.

So my question is what are my chances to get away without chosing a stronger tube and with no reinforcements. And if I actually should add something to make my head tube stronger, what should it be? Should I braze on a couple of rings on the ends of the head tube in a similar way the lugs are brazed?

I'm not sure the basis for many things stated in the Paterek manual. I started reading it once, and when I reached about 4 things I considered to be myths, I closed the book and gave it back to the guy I borrowed it from.

In the case of the 1.0 walled head tube, these are my observations and experience. First, you don't have a lot of choice in tubes for a 1" steerer, but thicker ones are available.

So... I have FBed tubes to the thinner head tube stock. The tubes you are joining to the head tube are thinner, so strength of the tube is not really the issue. I've never seen one tear from the head tube. But, due to the higher heat required, distortion is much greater. Reinforcement rings will help (not with distortion) but give you extra material for reaming. It's surprising how much distortion there really is in the HAZ. If your fillet isn't humongous it won't spread too far.

One thing I do is leave enough material above and below where the tubes join so no material is removed from the weld areas resulting in a thinner tube at that spot. And... I think reinforcement rings are necessary, especially in the 1.0 walled tubes.

JMO- someone may come along and say I'm all wet, but that's OK. It's just what I see. Not comfortable? Get a thicker tube.

As I start No. 1.5, I've been pondering this as well. I assumed it was to protect against ovalization at the headset not joint strength but, that makes sense too. I just received a few rings I ordered from Ceeway to braze onto the ends of the HT and they seem very nicely made. I think just some cro-mo tubing with the right size ID to fit around the outside of the HT would work as well. You could add some detail to this also if that's how you roll.

The issue to be aware of is ovalisation - with no reinforcement and the heat put in with filleting, you can end up with an ovalised head tube which causes problems after reaming. But it depends on your temperature control - it's certainly possible to fillet braze a lightweight head tube without ovalising it.

This was a 1.1mm wall head tube, with six tubes fillet brazed to it:

The problem with using a standard head tube for fillet brazing with an outer diameter of 1 1/4” is that after the inside of the tube is reamed to fit a headset, there is not enough wall thickness left to properly support the headset and it can ovalize or crack when the bicycle is being ridden. This is especially true if the head tube became distorted during brazing and the round reamer takes a little bit more off of 2 sides. Reaming makes the head tube too thin on its ends. It should be obvious that a lug provides that additional support on the ends of head tube.

The solution – if you still want to use the Columbus SL tube that came with your set – is to silver braze a supporting ring at the top and bottom of the head tube after the main triangle has been brazed. The proper size of this ring to have the right slip fit over the head tube is 1 3/8” outer diameter with a wall thickness of .058”. This tubing can be bought at Wicks or Aircraft Spruce online. Framebuilding suppliers used to have (and may still have) these rings available in a decretive design. This usually requires that the placement of the down and top tube move a bit more towards the center of the tube to make room for the ring.

The other solution is to buy a head tube with a larger outside diameter than 1 1/4” that has a wall thickness of 1.2 (Columbus) or 1.5mm (True Temper) thick. Don’t make the mistake of buying a thicker tube than 1.0 and still have the same 1 1/4” outside diameter (OD). It isn’t just about preventing distortion, it is about how much material the reamer removes for the headset so the ends would still be too thin.

I've not had problems fillet brazing a standard head ube, but I do like to use some of the scrap from trimming the head tube as a reinforcement so ham-handed headset installation won't be as likely to distort the head tube.

Thanks, everyone! That helps a lot. I think I'll go with brazing a couple of rings on my head tube.

@Doug Fattic
A couple of months ago you've mentioned that you frequently come to Ukraine to braze frames.
Do you mind answering a couple of questions about that now and then?
Like what kind of tubes do you use and do you bring them from the States or do you have some supplier near Kiev?

Sorry, can't send any private messages yet, don't have the necessary 50 posts.

Waterlaz, I didn’t notice that you were located in Kiev. Cool. We have a small bicycle repair and framebuilding shop in the back of a college campus (Ukrainian Institute of Arts and Science) about 25km west of Kiev. I was there last September and Jesse will arrive next week. We are making a kind of Dutch style transportation bicycle for pastors and other help society workers. This project started in 2000. Originally we bought bicycles from the XB3 company in Kharkov. I actually brought the head guys from Shimano Europe to meet with them so their bicycles could be supplied by Shimano parts. Eventually however they didn’t want to be bothered with our small order after ownership changed hands so we started making the frames ourselves. It is a kind of irony because if I hadn’t talked Shimano to go there, they would not have survived.

I have shipped the tubing from the True Temper tubing company here in the States to Ukraine. Most of the other parts like the dropouts and fork crowns are laser cut for us in Cherkassy. (This is a city maybe 200km south of Kiev for those not familiar with Ukraine geography.) They also helped design and laser cut and etch a prototype of the fixture I use.

I can send with Jesse the rings you will need for your frame. He will be fillet brazing a sample frame in Bucha for the next batch of bicycles we plan on making. He has been coming to my shop for a couple of hours a day for months so he can learn how to do this in Ukraine. This will be his first trip and will only be there for a couple of weeks. He will eventually go back later for a longer period of time. His goal is to also collect pictures and info to help make a more effective website of this project.

Well.. they are like a factory on life support now anyway. They used to make more than 100k bikes a year. And not just frames but all the things like cranks and hubs.

Thank you but I don't want to bother you with those rings. I think I can find the appropriate tubes myself. If not I know some people that can help me machine those. Maybe not from something as fancy as CrMo but I don't think this is very important.

Do you mean that there is some website already? This would be something very interesting to look at.

Waterlaz, Jesse left for Ukraine today. I sent the head tube rings with him. He is also bringing the right brass rod and flux to fillet braze our frames. I assume some of your knowledge of bicycle supplies in Ukraine might be useful for us? So lets keep in contact.

Wow. Thank you.

Sure. That would be nice. If there is anything I can help with just let me know.

Just in case. My name is Evgeniy and my number in Ukraine is 066 614 30 82.
Does Jesse stay in Bucha?

Yes, he is staying in one of the dormitories on campus. His wife came with him. Yesterday he was setting up a fixture to match the design of the frames we are making and practicing brass brazing with Yuriy who is in charge of our bicycle project in your country. One of our latest fixtures is in Cherkassy (where it was made) where they are designing and making a combination fixture and alignment table. I'll pass on your contact information so a visit can be arraigned.

Thanks a lot! The rings look great. I've brazed them on and cut the head tube. Now I see that the head tube hasactually deformed quite a bit.

I've almost finished my frame. Only the bridges are not brazed. And now I think that I might have made a big mistake. My ST-TT join is not lugged and I've got a fair amount of distortion after brazing.
I can insert a seatpost but it is being hold by those bumps near the joint so there is a nail thick gap on one side between the seatpost and the seat tube.
I've added a small reinforcement ring to the end of my seat tube but I am still afraid to use my reamer since the walls on the seat tube are so thin (0.6 mm only).
I there a good way to fix this?