LHthread

Hello all,

This is my first post. Apologies in advance if I'm asking questions that have been asked before. I've been a machinist for 25 years, and have lots of experience silver soldering all sorts of decorative and architectural assemblies. However, I've never built a lugged bicycle frame, and I'd like to give it a go, with the idea of making a few of them to zero in on a combination of size and geometry that suits my riding taste. I'm usually brazing bronze castings, or brass/steel assemblies. I tig weld when working exclusively in steel, so I'm a bit out of my depth here, and have a really basic question about jig and brazing strategy in constructing a lugged steel frame.

The methods I've read about involve sequential brazing steps, such as brazing the DT/HT combo, then the ST/BB, then the DT/BB. That's sensible enough, but would one ever want to braze all the BB locations at the same time, in order to only have one heat cycle and cleaning step? Is maintaining alignment too difficult? By extension, is it just not practical to design a jig that locates everything on the main triangle so one could braze all the joints in one operation? Is there too much expansion between lugs for that to work out? The brazing setups I've made have to allow for movement and distortion, but due to using different metals, in different sizes and masses and therefore different heat saturation, I'm just not sure if these experiences are a good reference. In a production environment, I'd think manufacturers would have jigs that were really comprehensive, so they could reduce setup time and cleanup time.

Back to the bottom bracket, I have a question about heat control. When doing each next brazing operation, do you ever have problems with silver starting to run in the previously set joints? If I'm working with a bronze casting, it has much greater mass than a steel bottom bracket, and I need to get a lot of heat into the part overall. I'm guessing it is easier to keep the heat localized in a steel lug. I'll soon be experimenting with all this, but it's always good to get some expert advice beforehand. Thanks for reading.

Nessism

Typically, the "jig" as you reference is used for tacking the frame together, then the full brazing/welding is done in a free state to allow for heat related expansion/contraction.

Regarding brazing all the BB junction joints in the same operation, I don't see any reason not to.

Personally, as someone without a full frame jig/fixture, I do one joint at a time, with alignment steps after each. This way I can avoid a massively misaligned frame after everything is joined together.

Andrew R Stewart 

Ed gives good advice. I'll add that yes, brazing adjacent to another joint with the same or a lower melt point of it's filler can be challenging. Part of the skill is reducing this.

I will braze the seat tube to the shell and then prep the rest of the main triangle to braze that together. I find this helps insure BB shell alignment and when I use brass for the ST/shell socket and silver for the DT and chain stays there's zero issues with filler melt out at the ST. I use this same method of different melt points fillers for other areas as needed.

If you're near me (Rochester NY) feel free to contact me directly or visit. Andy

LHthread

Thanks. Going step by step makes sense. I don't want some big misalignment to correct, and I don't really want to build a full frame jig either. What took my thoughts in that direction is a picture on the cover of the spring 2021 issue of BQ. It is of the Makino work shop in Japan, where they build frames for Keirin racers. They have this massive fixture on a table, with the frame oriented horizontally so the tubes are parallel to the table top, and it really looks like they might be doing the whole triangle at once.

LHthread

So using brass and silver side by side was a question I almost asked. Glad you mentioned this! I've never used brass as an alternative to silver. I'll have to practice this. Unfortunately I'm not near Rochester, although I am in state (Long Island).

Doug Fattic 

All of us use different methods to accomplish the same goals. We start with the teaching and tooling available and make adjustments as we make more. Unlike my buddy Andy, I'm not bothered with using silver everywhere including the bottom bracket shell heating it 4 different times, one for each socket. The advantage of doing it that way is to insure alignment and dropout length accuracy. I'm not reheating the whole shell every time but rather I'm concentrating heat on just one socket at a time.

There are 2 problems with brazing a joint entirely in a jig. The 1st is that it is difficult (maybe impossible) to keep repositioning the fixture that is holding the frame in the best places for brazing efficiency. And part of the fixture will sometimes be in the way making your heating pattern slower and more complicated. And 2nd it doesn't insure alignment accuracy anyway, that is determined by your heating pattern. Like Nessism does it, most of us tack in a fixture and braze free.

As a reference to alignment challenges, I refer back to the 70's when American framebuilding got restarted again. Reynolds required that those that buy 753 (thin wall heat treated tubing that can't be cold set) take a test to confirm they could braze a joint with complete penetration everywhere and end up with an aligned frame. When I talked to Terry Bill at Reynolds in Birmingham in 1977, he told me every single American that applied had failed the test. I'm sure that these pros after paying 75£ for the test tubes and making a complete frame and shipping it to England at their own expense put a lot of thought into their process. Their theory didn't match reality.

My primary tool in making a frame is an alignment table. I've also been refining a main triangle fixture ever since I came back from England with frame making tooling from Johnny Berry a master builder in England. In reality is just a much more sophisticated version of laying V blocks on a flat table over a full scale drawing to spot a frame together.

LHthread

Thanks Doug. It's good to know the heat can stay local enough to each joint location. In my normal work, I'm brazing with anything from a rosebud to a #1 and hardly think about it, but a bicycle frame is like a musical instrument, and I'm a bit apprehensive about getting things as right as I can. Regarding Reynolds 753, I was under the assumption that some amount of cold setting was part of the deal. Are you saying that when using heat treated tubing one has to nail the alignment all through the process? I'm planning on using 531 for my first frame, by the way, as it seems like a more forgiving alloy for a beginner. That's a funny story about the Americans failing the test. The Brits are top notch craftsmen, and there's not a very strong master/apprentice relationship here. But we are good at banging things out, or we used to be, anyway.

CrowSeph

sorry for the off topic sorta.
Can i weld small parts as steel rods (used to make replica of vintage bottlecages) with just the burner torch with gas propane?
I'am asking because i want to complete some little parts handmade, but asking to any professionist cost a lot of money and learning by myself would be very nice.
ps. i don't have any silver flux

Doug Fattic 

The 753 test needs to be put into context. 531 frames sold for small money after WWII in the UK. I bought my Hetchins frame for $75 in 1969. The market for 10 speed bicycles was to the poorly paid working class. A builder had to work fast and make at least one a day to make a living. They probably worked for a shop or shops that typically didn't have any expensive tooling. Frame alignment would probably be after the build. 531 would bend nicely.

Adult Americans didn't ride bicycles until 1970/71 when suddenly interest exploded. People that now wanted to build frames had to ether go to Europe where there were a lot of builders or try and figure it out on their own. Neither of those situations were ideal for knowing how to silver braze heat treated tubing (higher temperature melting brass would reduce the heat treatment). This is why Reynolds wanted to protect their new flagship tubing from getting its reputation ruined by a culture of inadequate techniques.

Americans in the 1970's were marketing to a different social class with a lot more money. They could charge more and as a result spend more time on each frame. It wasn't long before Americans did figure it out but it wan't right when 753 was introduced.

But to answer you question, yes thin wall heat treated tubing can be cold set a little during the build. Small adjustments can be made between spotting and brazing each joint. I've always considered myself to be very fortunate to have gone to a place in England that aligned on a cast iron surface plate during the build rather than just after it was made. That was good preparation for heat treated tubing when it became available.

Andrew R Stewart 

I never tried to melt steel with a propane torch, would you be using an air/propane or an Oxygen/Propane one? Big difference in flame temp. Either way in my little gas welding experience one wants a fairly tightly focused inner cone in the flame, set to be slightly oxidizing. The Propane flames I've seen are rather broad and with less a tight high temp tip. hence some of their appeal with those who use silver and/or build with lugs.

If you have the torch set up already than you should just try and see. If you don't and are trying to decide on what fuel to start your set up with and are going to weld (as in melt base metal) with no other info I would choose an Acetylene fuel. Andy

guy153

I don't think so. But you could probably braze it with that kind of torch. Is it basically a bent piece of thick wire that you need to join together and also attach to a mounting plate?

unterhausen

Vintage brazed water bottle cages made from wire definitely had their joins brazed or welded at the mounting plate. Seems to make sense even if you are making them from tubing.

Air/fuel torches might be hot enough to weld steel. You still want to support that weld. Brazing is the way to go, I think.