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.

DSC_0057.JPG

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

DSC_0070.JPG

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

DSC_0073.JPG

And the result:

DSC_0072.JPG


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.

SNV85652.JPG

[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?

[bencooper]

I haven't tested this, but my feeling is that a squint head tube would have more effect on the ride than a squint bottom bracket.. Of course you try to avoid either, but I alway worry more about getting the HT and ST parallel - my alignment system works off those two tubes, though I do it with a laser not a surface table.

[shand]

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?

Yes, well I guess that's where we come full circle :-)

Personally, I do it 2 ways, On my table I have a seattube insert set at known centre height. I also have a BB post (similar to a BB whipping post) but it isn't fixed to the table. Once the frame is fixed in the headtube support, I rest the frame by the BB shell face on the BB support. This tells me if the seattube is in plane with the headtube and if it's on centre height. The seattube insert acts as a go/nogo. I can check that the shell of the bb is perpendicular to the headtube by checking with a square on the table. If the shell is square but the face isn't, this shows up as a gap somewhere on the BB support.

However, there's an element to this which is slightly futile (also when using a BB face as a datum) in that the alignment of the crank is determined by the BB spindle located in a threaded shell. Unless you use a threaded BB post (and I know some do) then you're just hoping that the shell has been manufactured with the threads in perpendicular to the face (or parallel to the shell). The majority of our BB shells are now pressfit with no threads and that just creates a whole new set of issues!

Hope that makes sense. Here's a couple of pics to help explain.


SNV85653.JPGSNV85650.JPG

In addition to all that, I have a dummy wheel that I can use in the frame when it's on the table. Using a height gauge, we can check the wheel is the same height from the table around the circumference (parallel to the plane of the frame) and also that's it's on centre height.

We have specific tolerances we work to which vary at the different stages the frame is on the table. Post tack, post weld and post bridges. The actual alignment figures are recorded on a QC sheet that stays with the frame through production.

The key thing here is something Richard touched on which is that whatever you do, you need to be satisfied that you're getting the results you have confidence in. It doesn't really matter how you get there.

[bencooper]

Yup. Really, the important question isn't "Is this straight?", it's "Is this straight enough?"

[christo]

Gentlemen
first, many thanks for your feedback and inputs. For us amateurs (french way), this forum and the willingness of its members to share their experience is of great value.

I understand that the BB datum is not the best, and is highly dependent on many thinks. In my case, my table is certainly good enough for what i do (checked with a precision ruler, 1/50 mm over its length), and the face of the post seems to be reasonably parallel to the table (0.01 mm max according to my height gauge).

I also made sure that i was not doing wrong with the BB itself, and i slightly chased/faced the BB before checking that the frame was really leaning towards the drive side.

About the root causes, the miter on the ST/TT joint was no perfect as i had to pinch the TT to get a smooth transition with the ST sleeve. I do my miters with templates so far, and a pinched tube is not an easy case with this methode, as the tube is not really elliptical once gone through the vise. I also really believe that my brazing sequence needs to be improved, and even more my fillet brazing skills. I am not sure at all that i spend a homogeneous amount of time around a joint (acute angle takes more time for me) so i don't think that the heat is well distributed. I'll focus more on the quadrants

My question was more about this "witch wanding" thing, and i think that i got the answer : for an all-rounder it would be acceptable (Dave), but not good for a real mtb (Sean).

I am currently building an abrasive miter machine (i like building bikes and tools), so here is what I'll certainly do : I will leave the current frame, finalize my machine and will do plenty of nice miters, plenty of fillets, and then i'll restart from scratch.

Again many thanks for your help

All the very best

Christophe

[christo]

My question was more about this "witch wanding" thing, and i think that i got the answer : for an all-rounder it would be acceptable (Dave), but not good for a real mtb(Sean)

-Sorry, the last was Eric's recommandation

[MrkiMedo]

Gentlemen
first, many thanks for your feedback and inputs. For us amateurs (french way), this forum and the willingness of its members to share their experience is of great value.

I understand that the BB datum is not the best, and is highly dependent on many thinks. In my case, my table is certainly good enough for what i do (checked with a precision ruler, 1/50 mm over its length), and the face of the post seems to be reasonably parallel to the table (0.01 mm max according to my height gauge).

I also made sure that i was not doing wrong with the BB itself, and i slightly chased/faced the BB before checking that the frame was really leaning towards the drive side.

About the root causes, the miter on the ST/TT joint was no perfect as i had to pinch the TT to get a smooth transition with the ST sleeve. I do my miters with templates so far, and a pinched tube is not an easy case with this methode, as the tube is not really elliptical once gone through the vise. I also really believe that my brazing sequence needs to be improved, and even more my fillet brazing skills. I am not sure at all that i spend a homogeneous amount of time around a joint (acute angle takes more time for me) so i don't think that the heat is well distributed. I'll focus more on the quadrants

My question was more about this "witch wanding" thing, and i think that i got the answer : for an all-rounder it would be acceptable (Dave), but not good for a real mtb (Sean).

I am currently building an abrasive miter machine (i like building bikes and tools), so here is what I'll certainly do : I will leave the current frame, finalize my machine and will do plenty of nice miters, plenty of fillets, and then i'll restart from scratch.

Again many thanks for your help

All the very best

Christophe

If you have concluded that current frame is no go, you may consider to finish rear triangle in existing frame. I guess there are also plenty of errors to be made there, and stuff to learn.

[christo]

I guess there are also plenty of errors to be made there, and stuff to learn.

You bet !

[PLAIN]

Gentlemen
first, many thanks for your feedback and inputs. For us amateurs (french way), this forum and the willingness of its members to share their experience is of great value.

I understand that the BB datum is not the best, and is highly dependent on many thinks. In my case, my table is certainly good enough for what i do (checked with a precision ruler, 1/50 mm over its length), and the face of the post seems to be reasonably parallel to the table (0.01 mm max according to my height gauge).

I also made sure that i was not doing wrong with the BB itself, and i slightly chased/faced the BB before checking that the frame was really leaning towards the drive side.

About the root causes, the miter on the ST/TT joint was no perfect as i had to pinch the TT to get a smooth transition with the ST sleeve. I do my miters with templates so far, and a pinched tube is not an easy case with this methode, as the tube is not really elliptical once gone through the vise. I also really believe that my brazing sequence needs to be improved, and even more my fillet brazing skills. I am not sure at all that i spend a homogeneous amount of time around a joint (acute angle takes more time for me) so i don't think that the heat is well distributed. I'll focus more on the quadrants

My question was more about this "witch wanding" thing, and i think that i got the answer : for an all-rounder it would be acceptable (Dave), but not good for a real mtb (Sean).

I am currently building an abrasive miter machine (i like building bikes and tools), so here is what I'll certainly do : I will leave the current frame, finalize my machine and will do plenty of nice miters, plenty of fillets, and then i'll restart from scratch.

Again many thanks for your help

All the very best

Christophe

Hi Christophe ,

Just wanted to add up to comments if you are going to do a "witch wanding " thing again you should put a heat as close to the brazed joints as possible ,
cause there is a butt area that much stronger and thicker then middle of the tube and the frame will actually move instead of just introducing the bend in
mid section .
Also you might need to create a touch of stress to show the direction , in your case I would heat up top of ST/TT joint and top of DT just round the BB and place a block or wedge etc. under the HT to lift it up to the desired level .

Also might help if you align the center after each brazed joint , rather do the whole thing in the end .

Regards ,
Vlad

[Curt Goodrich]

One more data point- I've never fillet brazed in quadrants. Always have tacked on center line, tinned the joint, and laid the fillets all the way around. Zero issues with alignment. I think you're onto something with regard to uneven heating i.e. taking too long in certain areas. Like Vlad said, do a joint and check the alignment after it's cooled. Adjust if necessary and move on to the next joint. Rinse and repeat. Keep up the good work.

[Will Neide]

http://www.velocipedesalon.com/forum...ues-18650.html

Some useful info from knowledagble folks on sequence.

[e-RICHIE]

http://www.velocipedesalon.com/forum...ues-18650.html

Some useful info from knowledagble folks on sequence.

Thanks for that pointer.
This place really has a lot of good info cached atmo.
Not all of it works for everyone, but as a resource, the board rocks.

[ChrisJPB]

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

Chris Bernique
Charleston,SC.