Messy fillet brazing and (bad?) solution...

[christo]

As a newb and a hobbyist, i climb the learning curve mistake after mistake. My current project (29er fillet brazed, Zona) is a good example. So long story short, here is the problem : after tacking the front triangle came out absolutely straight from the jig according to my alignement table.

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HT to ST was also still OK (less than 1 mm over 1m) after fillet brazing, so i did the finish work and got ready for the next step. This said, i noticed during the prep of the stays that the front triangle was not seating really well on the jig, so i went back to the alignement table to not only recheck that the HT was parallel to the ST (which i normally do as per previous pic with 2 cones and a 1m rod), but also that HT/ST/BB were in the same plane (this for some strange reason I rarely do, assuming that the HT would be in the right place...). And obviously they are not : it turns out that the entire HT is nearly 4mm off center to the drive side

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At this stage, cold-setting would be insane. Leaving the front triangle as it is would also be a bad choice given the importance of misalignement. And in that case, what would be the next step : brazing the rear end in the plane of the BB (meaning twisted cranks), or in the plane of th ST/HT (meaning twisted....I don't really know how twisty this would be) ? I was close to scrap and redo (i actually ordered a new set of tubes at Ceeway already) but then i remembered reading that some guys re-aligned tubes only with heat.

I clamped the frame to the table, and slowly put heat at different spots between the braze-ons until the frame got back to normal. No flux as i wanted to see what i was doing. Heat until red shows up only. 3 spots. Those spots are easily visible here

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And the result:

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So my question to you guys : should i continue with this frame and go to the rear end now (needless to say that this bike will be mine), or should i assume that the structure of the front triangle has been so damaged that it should be scrapped ?

Thanks for your inputs

Christophe

PS : Dave Bohm already told me to work per quadrants to control the distorsion. I totally get that of course but need to practice more

[Eric Estlund]

I'd call that one dead. You've just introduced new heat affected zones in the thin part of the tubes at intervals, and in one direction.

[Eric Estlund]

You mentioned it was good after tack, but pulled during the brazing? My first thought is to check the miters (for phase and gap), my second is to revisit your brazing sequence.

[VertigoCycles]

There's no real way to completely diagnose this over the internet. You have to be aware of all the realities of your own sequence. No doubt, this was a good learning experience, especially seeing that you can heat the sides of the tubes to induce a bend in them (though it's a bit misguided).

Take the time to consider the warpage of your BB shell and how it relates to your alignment check. Get out your caliper and measure across the top of your BB shell and then at the bottom...note the difference. Do this after you tack and then again after your fully braze the DT and the ST to the shell. Note the difference. If you're using an alignment system that relies on the face of the BB shell as a datum, and that datum is no longer parallel to the centerline of your frame, can it be trusted?

Your front end might not be as bad as you thought it was...the point is that while it's great that you're self-critiquing your brazing process, don't neglect the alignment aspect of it, the tools, what surfaces you're using to read alignment and how heat has affected them. Did you buy that table or make it? Have you verified that the face is parallel to the table itself? I ask because I've seen a brand new $8K Marchetti table with the face of the whipping post 0.004" higher on the bottom than the top which prompted the owner to chase his tail for months wondering why no frame checked on the table appeared to be straight.

[dbohemian]

Hi Christophe,

As some of you may know, Christophe was a student of mine for a lugged course. He has been doing great things and I am happy to see him working in other techniques as well.

As you already concluded most of this deviation was due to either miter fitup or brazing sequence. I know Christophe is very thorough so my guess would be the later. Practice breaking down each joint into four quadrants and brazing 90 degrees at a time, then working the opposite quadrant. Its a lot of moving the frame around but with practice doesn't become so cumbersome.

I use the head tube for my datum. Learned that from Mr. Pacenti and Jamie Swan and it really works a whole lot better for me. What Sean mentioned above is what can commonly happen when one relies on the BB faces/bore as the datum. It is true that it is possible for the BB to be out of plane while the rest of the frame is well within tolerance but unless its severe you will find that it will cause very small discrepancies at the crank and is preferable to setting the entire front triangle back to the BB as a reference surface.

The "witch wanding" IMHO may not have been as bad as one may think. I would think it fine to use the frame for personal reasons/get around the town kind of bike. Yes, the frame has become annealed in these zones but that is probably o.k. Good news is that it won't fail catastrophically and if you keep a close eye on it, should be safe.

Keep it up.

[shand]

Take the time to consider the warpage of your BB shell and how it relates to your alignment check. Get out your caliper and measure across the top of your BB shell and then at the bottom...note the difference. Do this after you tack and then again after your fully braze the DT and the ST to the shell. Note the difference. If you're using an alignment system that relies on the face of the BB shell as a datum, and that datum is no longer parallel to the centerline of your frame, can it be trusted?

I've never understood how referencing off the BB shell works. I know almost everybody does it but it doesn't make sense to me. When I was setting up my alignment system when I was starting out, the www wasn't really much use for researching these things and I had nobody local I could ask. I settled on an alignment system using the headtube as a datum and I still use that. It just seemed to be thing that made the most sense. If I was trying to do this on my own in isolation, I can't imagine ever coming up with the idea of using a face of the BB.

I'm not knocking those that do but when ever I've worked on tables that do use the bb face, I can never get repeatable results. It feels like you're constantly chasing your tail at each stage of the process.

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[e-RICHIE]

I've never understood how referencing off the BB shell works. I know almost everybody does it but it doesn't make sense to me. When I was setting up my alignment system when I was starting out, the www wasn't really much use for researching these things and I had nobody local I could ask. I settled on an alignment system using the headtube as a datum and I still use that. It just seemed to be thing that made the most sense. If I was trying to do this on my own in isolation, I can't imagine ever coming up with the idea of using a face of the BB.

I'm not knocking those that do but when ever I've worked on tables that do use the bb face, I can never get repeatable results. It feels like you're constantly chasing your tail at each stage of the process.

It's a standards thing as in, you set your own. There's no real need to prove that the forth and fifth check is the exact same (as in a zero reading) as the few that preceded it. And, it doesn't matter if you flip the frame on a unit deemed okay and the other side isn't a mirror of it owing to the faces not "exactly" opposing each other. The same can hold true for head tubes. The bore that permeate the top isn't always in the same plane as the one below it, but a fork and headset will still fit nicely and turn smoothly enough.

I use the bb faces and a M+L table that I had reground a year after it arrived. That's good enough for me. I want to know that the biomechanical axis (the rider, pedaling over the bicycle) is centered and square with the central movement that the cranks rotate around. By default, the traditional whipping post ordeal permits that. The frame alignment works outwards from there.

Both methods are fine.

And just as no two M+L tables, or Bike Machinery tables, or FNG granite tables will each inform of the the same alignment checks, using the head tube method will also have variables. All that matters is what you do in your man cave. Set a parameter and meet or exceed it.

[EricKeller]

I know the bb shell is a poor datum after brazing, but then again, if you use the head tube how do you make sure the bb shell is orthogonal to the plane of the frame?

[ChrisJPB]

I saw one of your road bikes the other day. What a work of art!

Chris Bernique
Charleston,SC.

[christo]

It took me some time but i finally finished this project, for a good part thanks to your advise. I scraped the initial frame and used it to practice more on fillet brazing. I think that part of the distorsion was due to poor miters. As I don't have much time to practice hand mitering until it gets perfect, I build an abrasive mitering machine that works pretty well.

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I then practiced on scrap tubing (the picture only shows a little part of the practice) until i feel more comfortable with heat control and also fillet finishing.

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I then went back to the frame with a new tube set. When done, I couldn't resist to assemble the bike without paint, to see if the geometry fits me well. So far so good, it just needs a seatpost with more setback and a slighlty longer stem.

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My only concern (and question to you guys) is about a few tiny holes in some fillets .

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It didn't show up during practice brazing, but I think I was a little nervous with the real thing and my heat control wasn't always perfect. Question is : does it matter if I leave those holes as they are knowing that the frame will get powder coating ?

Thank you for reading

Christophe

[Chauncey Matthews]

Congrats on finishing your first!
Yeah you can leave the holes and the bike will be fine, but be forewarned, if you think are noticeable now they will be twice as glaring after powdercoating.
Also, it looks like you have your seat clamp on the .6 part of the seat tube, its going to crack right along the stress riser at the top of the sleeve. Get a bigger clamp that fits the sleeve and cut the slot a little longer...easy to do now that it's not painted.

[steve garro]

Yeah you can leave the holes and the bike will be fine

You can get porosity to porosity cracking, actually.

- Garro.

[Chauncey Matthews]

You can get porosity to porosity cracking, actually.

- Garro.

True, I should've added "because its your first frame and its not like you'll be riding it for years and years..."

[einreb]

Question is : does it matter if I leave those holes as they are knowing that the frame will get powder coating ?

You can fill them with JB Weld before powder coating.

[David Tollefson]

You can fill them with JB Weld before powder coating.

Or silver.