This is my first post to bikeforums, and I am utterly uninformed about brazing and metallurgy in general, knowing only what I've been able to glean from one evening of Google searches; basically I'm ignorant.

I work at a pottery studio, and I'm curious whether it would be possible to create a lugged steel frame in a large bisque kiln. Its probably an absurd concept.

Leaving methods for assuring proper joint alignment and stabilization, etc, to the imagination, if I were to use a high silver content, low-temperature brazing wire and a relatively thick walled tubeset, like classic 531, would it be possible to securely join the tubes by firing them in a kiln at 1200-1300f and allowing them to air cool, without causing the frame to become brittle or oxidized? If it would be possible and not totally illogical what sort of preparation would be involved?

Also what is the 'heat treatment' that differentiated the 753 tube set from Reynolds 531? I imagine it was something other than simply baking the tubes.

Any help or comments would be appreciated.

Some old school production frames were built using a furnace brazing process. Frame was placed on a rotary table and rotated into a furnace for heating, after the metal is up to the proper temp, the table rotates again removing the frame from the heat and brazing metal is added. My understanding is that one area of the frame was heated at one time, not the entire frame at the same time. Some of these frames used a internal fillet brazing technique; rings of brazing alloy were placed inside the joints which flowed out during heating.

Hope this helps in some way.

Ed

mercian still uses open hearth brazing
http://www.merciancycles.co.uk/craft.asp

Brazing in a kiln? Won't you end up with a layer of molten metal on the floor?...

No, I don't imagine I would end up with molten steel, though my boss would probably kill me if I did.

The kiln would slowly heat to 1250 or 1300 degrees and immediately begin to air cool after reaching the desired temprature, and unlike a torch there would be no risk of overheating. The silver braze would hopefully melt and spread enough to bond the lugs, but the frame tubing whould be about 1000 degrees away from liquifying. My fear is that heating the entire frame would significantly weaken the steel, but other than that I am fairly certain that it could be done without much difficulty.

I was aware of the Mercian process, not what I'm imagining exactly; my plan is to wrap very fine brazing wire tightly around the ends of the tubing, then to insert the tubes into the lugs, which would need to be heated enough that they would expand to accomidate the increased diameter. Perhaps bisque moulds could be used to hold additional braze-ons in place.

So ultimately my question is would heating Reynolds 531 or an equivlent steel to 1300 degrees make it weak?

This would just be a fun project for me, designing and building my own custom touring frame cheaply.

Thanks.

nome.king-
You might consider experimenting with something other than a complete frame. For instance, I believe it is at bikelugs.com that lugs for making threadless stems are sold.

Sounds somewhat similar in principle to what Masi did with the 3V, but they put a spring of silver wire in the joint before brazing, they didn't wind it around the tube. I imagine that getting the proper interference fit between tube and lug would be impossible, given the 1/16" thickness of typical silver rod. How small can you go with silver? Probably not something in the 1 or 2 thousands of an inch you're thinking of.

Fred Parr described something similar; the Schmidt (spelling??) technique for making internal fillets. He would wind Allstate 11 rod into a spring, saddle-form it to mate up against the intersecting (head?) tube and then lightly tack it with silver into the other (down) tube. When you heat the tubes to create the external fillet, it makes the internal fillet too.

He also said to make use of gravity. And there's your next problem. How would you use gravity to your advantage to draw the filler through the lugs?

capillary action is not gravity dependent; the filler
follows the heat. you can "walk" brazing material
vertically as long as your heat source so directs it .
e-RICHIE©™®

Thanks for your comments and suggestions. The smallest appropriately composed silver rod I've seen so far is 1/64". It probably is available in smaller diameters.

Wouldn't heating the lugs to about 500f and perhaps chilling the tubes cause at least 2/64s of an inch of expansion/contraction temporarily? I use this method for installing steel crown races, and the inner diameter increases visably. After cooling they are tightly mated to the fork. Condensation might be a problem if the tubing was cooled.

The kiln would apply heat very evenly, which hopefully would cause the filler to spread in all directions.

It may also be possible to make clay funnels to guide the silver into the lugs rather then attempting to put it in place before hand.

I will probably get a fork crown and blades to experiment with. Or building a stem from the lugs at bikelugs.com would be nice and I would have a better chance of survival in case of catastrophic failure... but they are rather expensive.

Perhaps I should just learn traditional brazing?

Thanks again.

LOL! I'm ignorant AND fascinated by the process of creating a frame.
Also, as a silversmith used to creating wearable art, the thought of riding my art is magnetically attractive to me.

I often use silver paste solders containing 56% silver or higher (http://www.myuniquesolutions.com/page6.html - not my site, just an example) I imagine this might be used much like the coiled silver solder placed inside the lugs.

I'd imagine that this would be worth a try.

FYI to those interested, the clearance between the lug and the tube depends mostly on type of lugs used. If the clearance is on the tight side, 2-5 thousands, a high silver content brazing material like 56% is commonly used (by custom builders anyway), for looser fits, brass is typically used. As Richard mentioned, it's the capillary action that pulls the brazing material into the joint after it turns into a liquid so the diameter of the wire rod in not that important. The material is fed in from the outside and the capillary action pulls the material into the gap formed by the lug and the tube thus there is no need to make a coil in the inside.

Hope this helps.

Thanks, Nessism. You and Richard are definitely correct about the capilliary action. I'm always amazed at the way a hot tight joint will suck up solder.

Nome.king, do you have any experience in working with enamels? After soldering your kiln might be just the ticket to set off a well cut lug with cloisonne enamels.

oooooo....

An enamled frame would be sweet.

What temp does the enamel melt at?

I've discovered the perfect frame material, True Temper OX Platinum, which supposedly gets stronger at these temps rather than annealing and losing temper. As soon as I can afford to I will buy a set from henryjames.com. It costs about the same as what my source wants for NOS 531.

The cloisonne idea is wonderful. The only instances I can find of it being used on bikes are the headbadges of Rivendells and Bike Fridays.

You've got me imagining something with the intricate detail of a Russian icon. Much more exciting than a powder coat. Can this type of enamel withstand prolonged exposure to rain, and is it capable of withstanding impact? My goal is to build a long-distance loaded touring frame, so it would definitely get exposed to nature.

Oooh, yes, an enameled frame would look sweet. But it would have to be for show. Enamel would be too brittle (it is glass) on a flexing frame.

It would be possible to set off cut outs in lugs with enamel. The fusing temps of enamel are lower than pure silver or copper, as both are regularly used as the base to build an enameled piece.

Dichroic glass would also be very useable as its slumps and flows at lower temps than even the enamels.

I like the enameled headbadge idea. I'll have to work on my enameling skills (mediocre at present. I'm just learning as shown by these three enameled .999 silver leaves show. http://users.cis.net/coldfeet/3leaves.JPG )

What you are suggesting is to bake the entire frame, lugs, solder and tubes at the same time?

I would seem to me that you would lose control over the brazing process by doing that while gaining nothing. And the frame would not be able to be worked under those conditions, so adding more solder wouldn't be possible once firing was underway.

I really don't see an advantage with that, even in time savings.

What I would be curious to know is whether a reliable lug could be made in a sintering oven using powder metal technologies. Sophisticated sintermetal technologies exist already that are able to impart varying qualities (hardness, rust resistance, etc) of metal to different parts of a single sintered piece by varying the content of the component metals, specifically in stainless steel applications.

The primary reason for using the kilns is that I have access to them, and I do not have access to welding equipment or a frame jig. It would also reduce expossure to noxious fumes and chemicals. Also, the kiln is large enough to hold up to perhaps six 64cm frames, and if the process could be streamlined it could potential allow me to build several bikes each week.

Certainly ensuring enough braze went into the lugs would be tricky, but if it were necessary I think I would be able to create glazed bisque trays to hold the silver in place without contaminating it, to ensure it got sucked into the lugs.

I really hope this works for you nome. I think it is very cool idea, I wish you luck with it and hope you post alot of pictures of the process.

Most production brazing (of non-bikes) is done either in batch ovens, or in continuous conveyor ovens. The pieces are assembled with precut flux pieces and precut filler metal pieces, and then heated up. They then come out the other end brazed. Not that that has anything to do with bikes, but brazing entire assemblies in ovens is very common today, so your idea isn't all that crazy. Here's one company that specializes in this kind of work http://www.californiabrazing.com/

I've seen a short video on this process several times on TV. It's part of a series we get called How It's Made. One thing you would need to look into is whether the tubing you have in mind would tolerate these temperatures with thin wall tubes without gas purge. In the video I saw they we using a flame, and flame concetrates the heat, and also can be run so that there is a gas shield effect. These were also pretty low quality frames so they may have been rugged enough. One get's some oxidation at 900 degrees. I notice that california brazing has some pressure vessles.

After you made the first frame or 2, I would reccommed some precision measurements to ensure that there is no movement or warpage...