I’m nearly ready to start building fillets on my first fillet-brazed frame. I’ve got the main triangle and the chainstays tacked & tinned. I’m wondering where I should start trying to build the fillets - BB, seat tube/top tube cluster, HT/TT, HT/DT, or something else? Does the sequence/order matter much at this point? Where would you start, and why?
Thanks!
-Jim G
-take a break here if you need it as I prefer to then do both HT fillets one straight after another especially on HT sub ~150mm length
It’s not the only way, I’m sure some builders will chime in with alternate options, but this is my preferred order and one that I find is most efficient and minimizes distortion and need for alignment (although that also comes down to heat control and time spent per joint).
I’d put the seatstays on before making the chainstay fillets. Actually never tried it without, but it seems to invite movement out at the dropouts that you’d have to deal with by bending them back where they belong before you could put the s.stays on.
I’ve never understood this “tinning”. What you call tinning, I’d call brazing. Why let the joint cool off, just to heat it up again later? Not a rhetorical question, if there are reasons that I’m not seeing, lay 'em on me. You know the old saying, “Strike the fillet while the iron’s hot”!
I have made a few thousand fillets and not a one ever came apart — that I know of! Even later in “My Brilliant Career” (movie reference) when I was making the fillets smaller and smaller, even on tandems and MTBs (and MTB tandems). Big fillets make a frame weaker, not stronger. I think this is well-established. Big fillets are easier to smooth, but smoothing fillets makes frames weaker too. So keep the goal in mind, to lay the fillet down quickly and smoothly enough that it doesn’t need any filing, die-grinder, dynafile, cartridge roll or what-have-you. Do that when you have to, but keep it to a minimum and don’t dig a trough into the steel all around the joint.
Oh and don’t go back and re-melt a fillet to smooth it. Better to file off lumps than to fix by adding even more heat, and time-at-temperature.
I agree that minimizing the heat put into a joint makes it stronger. I also know that (to a point) smaller fillets are generally better.
That said, this is my first fillet-brazed frame (and only 2nd frame beside the lugged bike I built at UBI). I am not a confident fillet brazer – I am taking things slow and following the examples and processes shown by Paul Brodie and Thrifty Framebuilder in their YouTube videos – both builders tin the joint before brazing it completely. Brodie likes to tin using nickel silver – I think his rationale is that it is more runny, so it better wicks into the joint, helping to ensure good penetration. I am following that example.
Once I’m more familiar & comfortable with the whole process, I will probably skip the tinning step.
Thanks!
-Jim G
Oh really! That’s interesting, wouldn’t have guessed. I’ve used a pound or two of nickel-silver (which I hope everyone here knows, contains zero silver) over a few decades, but thats a drop in the bucket to how much brass I’ve used. I never really compared their “runniness” head-to-head but I would have guessed brass was, if anything, a bit better that way. Maybe I should experiment.
The one thing beyond dispute is that NS is stronger than brass, but that’s moot once the fillet is big enough to exceed the strength of the steel.
Any small difference in capillary action is pretty moot too, since brass goes under and inside miters practically instantly. No more runniness than that is needed. But hey, if it works for Paul, who am I to question it? There’s definitely no harm done from mixing the two in one joint, so why not?
I even made one lugless frame, my 3rd-ever frame back in the '70s, with 100% NS for the fillets. Bit of a bear to file those fillets, and the liquidus is higher so a bit more heat damage to the steel, so I wouldn’t recommend it.
But all of that is orthogonal to the question of when to fillet. Even with the combo of two different fillers, I’d still fillet while it’s hot from the first step
I like to have the whole frame tacked in the fixture (inc seatstays). If I were you right now my first job would be to align the rear end then affix the seatstays then recheck alignment before fillets.
FWIW I am also in the ‘no tinning’ camp. And I keep my tacks as small as possible in order to reduce the initial heat during tacking and also to reduce the heat it’ll take to bring the joint (and tacks) up to temp during braze out. I also find it easier to keep my fillets regular when I can fly straight through a small tack than having to manoeuvre around/ over a large one.
My sequence:
Under BB-DT
Behind ST-BB
Join the two sides starting from the oppo side I just finished.
CS-BB insides then outsides
SS-ST insides then outsides
Under TT-ST
Top TT-ST
Join the sides starting oppo where I just finished.
Top TT-HT
Bottom DT-HT
Under TT-HT
Top DT-HT
Dropouts last, following similar rule of top/ bottom before sides
I don’t do a great deal of preheating and braze with a constant flame so the joint gets hotter as I go. So for me it works to start in the ‘lappy’ (open) side of the joint and work toward the tight side. If I go the other way I’ll over heat the lappy side and have to slow down which interrupts the fillet and it’s bad times.
But since I don’t wanna do the sides of any joint first (usually), the ‘ears’ of the TT-ST and both TT and DT-HT get hoooot. So I turn my flame down for those.
I guess it’s heat management vs alignment. You have to figure out a schedule that keeps both camps happy.
Edit: oh and I come back for the DT-ST strap last of all. Just a weird thing I’ve always done as I didn’t like brazing such a tight joint before the whole frame was solid and it wasn’t gonna alter the alignment.
How do you align the rear triangle if it’s only tacked? Should I be worried about breaking the tacks holding the chainstays?
Thanks!
-Jim G
Personally I don’t align when tacked (or at all, really). If I do need to, I use heat.
But I’d assumed your CS were tinned? Which should be enough to give a small tweak by hand (if necessary, may not be). If you need to do more than a very small persuasion it’s best to use heat carefully 
Same applies if it’s tacked really.
The reason I like to have the SS on there prior to fillets is that you’ve got more ‘self fixturing’. ie as long as everything is straight and tight when it comes out the fixture, it’ll stay that way. My previous thoughts were an attempt to replicate that now that your frame is out of the fixture.
I am aware that lots of folk put the SS on last - that’s just not how I like to do it. More than one way to skin a cat 
maybe somebody who does it that way could be more help at this point.
Interesting! Do you also add the seat and chainstay bridges? Or is that done last?
The chainstays on my frame are actually just tacked so far. I am planning to tin them. Alignment-wise, I do need to move one of them a few mm’s out. I suppose if I start tinning on the outboard side of the BB, it’ll pull the chainstay in that direction?
Thanks for all the advice – it’s really helpful!
-Jim G
That’s an intriguing thought… I don’t add the bridges until after fillets (along with the brake tab etc) but that’s mainly to allow access to the tight spots inside the stays. It probably makes sense to add them once everything has been brazed to avoid introducing any weird tension but if I could I probably would add them while in the fixture 
You might be able to correct that chainstay with your sequence, yeah. If it were me though I’d try to coax it into place beforehand.
No worries at all, best of luck with it 
Hi there!
Two observations for the next time.
Dont do tining, especially with nickel silver that has a higher melting point than brass. That will count as a first pass, your final fillet the second. Not good to the alloy for a number of reasons!.
Try tacks, small ones:
Depending on the part of the frame and the possible alignmet direction i put 2 or 3 so in case one fail theres others to contain (specially important with silver!).
The alignment fase of the tacked frame will tell you where the frame wants to go. You can try when brazing try not to let it go where it wants. Sometimes it works, sometimes it doesnt.
I used to braze in segments but i been doing for some years all straight and fast, in and out, and the frames come, after some final alignment, perfect (or as good as i like them).
Keep it up and keep sharing!
Andrés
Wow, there’s some really great advice here from experts. I just thought I’d mention that at UBI they taught me that the tacking sequence for the front triangle is pretty important. You’re well past that point now, but it’s worth thinking about for next time.
If you haven’t seen this, check it out. Thom’s brazing is something else.
Oh shit, didn’t expect this to come out here thanks @scharencycles.
I wish I had more time to do stuff like this. You can’t really see the benefit of my preferred method when it’s done along a piece of tube, when done across a joint it makes a lot more sense.
Thanks for that. I took the lugged course at UBI and now I’m wishing I had taken fillet brazing instead!
Shoot, @TDB this isn’t the video I was thinking about. The thumbnail threw me off. Maybe it’s on instagram? I have definitely seen a video of you doing a pass on an actual tube junction. I’d love to see more.
Ah yeah there are a few on my insta I think.
Thanks, I’d love to film some more but finding the time is tough at the moment. I’ve never been very good with a camera either so it makes it all a bit of a faff for me. Maybe one day I’ll hook up with somebody who can shoot while I braze.
Do I understand you correctly that you first tack everything in the fixture, then take the fixed frame out of the fixture and then make the fillets?
Yeah that’s correct
All great advice here. Not sure if anyone mentioned but a reminder that super accurate mitres go a hell of a long way to getting a frame straight. The tighter you can get them the straighter your frame will stay under heat and cooling filler.
