distortion after brazing lugs

[suicideking]

So i brazed my first front triangle today, tinned the joints on the jig then finished on a stand. let the joints cool and then soaked them overnight to loosen up the flux, when i put the triangle on my BB tower to check for square, the distortion is considerable (3/8" at one point from square). Does that mean the joints got too hot? Were done in the wrong order, were not evenly heated? or a normal change in standard chromolly tubing and lugs?

The frame is a lugged 58 to give you an idea of the size, and the headtube seems to be the most out of round at this point.

[EricKeller]

tinned doesn't sound right with lugs. Do you mean tacked? Did you check your alignment when it was tacked? Your tacking technique may not be up to the stresses of brazing. I can't even imagine what tinning a lug would be like. You might want to tell us what equipment you were using.

[suicideking]

maybe tinned isnt the right term, i only brazed small portions of each contact point on the lug not wanting or being able to get behind the jig entirely in some places. I always thought that a partially slipped solder joint vs completely pulling the filler metal through was considered tinning (plumbing term maybe)

using the tip that came with the torch so i suppose the tip could be changed or adjusted. Using a paste flux from gasflux and 1/16th filler rod. I did fillet braze the ST TT junction, that took more heat then i would have liked due to the small dia filler rod.

[Andrew R Stewart]

Tinning usually means the surface application of solder (braze) on one of the pieces before the two pieces are brought together. This insures complete solder adheasion and quickens the joining time. It can also mean the initial flow of braze around (and into, to establish the "internal filit") two tubes to then have a filit built up as a second step. Tacking is usually meant as the small and localized spot of brazing that is used to hold tubes is place with each other to allow pre full brazing alignment and then hold this alignment during the full brazing. usually done on the frame's centerline to minimize the side to side forces that can cause twists.

Did you apply the flux (as a paste) between the lug and tubes? Or just on the outsides?

The tubes can shift during brazing if they are not tacked or pinned or otherwise held well enough in place. A tack can melt before the flow elsewhere solidifies enough to replace the tack's holding job. Metal expands and contracts with the heating cycles, unevenly if the application of heat is also uneven in location, amount or time. Rod size usually is more an issue of how long it takes to melt enough braze to flow and fill the joint. Independent of distortion unless added unevenly.

I do wonder what you mean by "(3/8" at one point from square)". Is this the amount of twist between the ST and HT measured along the HT length? Or the amount a tube is off it's intended angle at it's end (say the ST no longer being square with the shell)? Different issues and precesses to make right the next time. I do assume you've practiced multy jointed structures before, or that this first is really a practice. Andy.

[Andrew R Stewart]

One more point. The head tube (as well as seat tube) can distort from round from the differing thermal mass on the front side VS the back side. One reason to use thick walled tubed for your first frames. They both resist the ovalizing and allow for a good head set cub reaming after some ovalizing happens. After brazing the lugs fully you can apply some heat on the front side (of the head tube around the lug's band) to help equalize the heating and distorting potential. This is why many beginers use Silver as it's lower temp reduces the distorting forces. Still I think one should get good at flowing brass before going on to an actual frame. Andy.

[suicideking]

Thanks for the information. i suppose what i was doing was a form of tacking using that description and the entire joint could have slipped once out of the jig. I did apply the paste flux to the inner and outer areas of the joint. By out of square i am utilizing a lapped piece of granite as a measuring table, i machined a tower to hold the BB off of the stone at a uniform angle to the table, then use a vernier height gauge to measure where i expect the top of the head tube should be in relation to the BB center. one corner is at least 3/8"s lower than where i was expecting it to be (angled) . i suppose i can try and massage the head tube to straight, i am sure with that thin of tubing and that amount of heat there is bound to be some distortion that requires massaging once brazed, just wondering where that measurement fit in the relation to things. As i said, it is my first attempt and felt like each join i did got progressively less sloppy. I did practice alot of fillet brazing on test tubing, just need more practice maybe

[e-RICHIE]

how much brazing have you done before this ^ ^ ordeal atmo?

[Andrew R Stewart]

I believe that you are discribing a twist between the HT and St (as held by the shell). Uneven heating and/or slipping parts during brazing could do this. My suggestion is to use this as a learning experience. Try to straighten the frame and see what happens. Then cut it all apart, note the spring apart of the first cut tube ends. Continue with the joints to check braze filling. Save the tubes to continue practicing. Consider bigger tacks, pinning, and/or more robust tube holding next time, align after tacking and try to balance the application of the flame around the joint to reduce unevenness. Andy.

[suicideking]

Yes it is twisted, i assumed from the heat, i understand it could have been moved now and brazed at the wrong angles. I like the idea of cutting the tubes up after to see what kind of spring there would be in the cut tubes. I still need to finish the stays. I have welded plenty and brazed alot of heavier materials mostly with fluxed rod, most of the joins were not for aesthetics. I guess its something you have to get used to. I appreciate the tips.

What is atmo?

According to my opinion?

[e-RICHIE]

Yes it is twisted, i assumed from the heat, i understand it could have been moved now and brazed at the wrong angles. I like the idea of cutting the tubes up after to see what kind of spring there would be in the cut tubes. I still need to finish the stays. I have welded plenty and brazed alot of heavier materials mostly with fluxed rod, most of the joins were not for aesthetics. I guess its something you have to get used to. I appreciate the tips.

What is atmo?

According to my opinion?

yes - ps more than likely the distortion is not from brazing but from assembling tubes and interference fits under
load. in plain english, the warping potential could be introduced even before the torches were turned on atmo.

[Curt Goodrich]

I didn't see this but I'm assuming you brazed this with brass? It's difficult to warp the head tube with silver. Brass certainly takes a little more deft touch. What works for me is to tack in the jig on center line. For the tack, I flow brass or silver across the joint. A tack needs to be substantial enough to keep the alignment during the early stages of brazing. Let the triangle cool in the jig. Check the alignment before brazing. Then start brazing 180 degrees from the tack. Work your way around the joint without allowing the whole thing to be molten. Keep practicing and taking note of your procedures. I like to start with the bb shell. Then the top lug. Then the bottom lug and finishing with the seat lug. It gives me consistent results. Others follow a different pattern with good results. What's important is to find what works for you.

[suicideking]

I didn't see this but I'm assuming you brazed this with brass? It's difficult to warp the head tube with silver. Brass certainly takes a little more deft touch. What works for me is to tack in the jig on center line. For the tack, I flow brass or silver across the joint. A tack needs to be substantial enough to keep the alignment during the early stages of brazing. Let the triangle cool in the jig. Check the alignment before brazing. Then start brazing 180 degrees from the tack. Work your way around the joint without allowing the whole thing to be molten. Keep practicing and taking note of your procedures. I like to start with the bb shell. Then the top lug. Then the bottom lug and finishing with the seat lug. It gives me consistent results. Others follow a different pattern with good results. What's important is to find what works for you.

This^ is a fantastic response. Thank you

[Eric Estlund]

Don't underestimate how slightly out of phase miters can pull the bike way out. To back up what Richard was saying- if the bike wasn't cut and assembled straight, there isn't much to be done after that. If you are seeing 3/8" of head tube twist I would venture that yu are having more of a coping issue then a heating issue (though likely both on frame 1).

At this stage (ie- just getting started) treat them as two separate skill sets (1. Mitering and 2. Brazing) and drill for both.