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Brazing technique for fillets

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Brazing technique for fillets

Old 02-05-20, 04:44 PM
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Nice dimes! I really enjoyed using a gas fluxer when I was at frame school. So bad ass!
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Old 02-06-20, 10:11 AM
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David Bohm on Flicker, moves the torch a minimal amount, great heat control(understatement), probably just moving the puddle along with complete control while dipping the rod in. He filmed this in a timed speed contest/bet against another builder tig welding a joint, most likely takes a little more time but who knows.I'm posting as many vids of fillet brazing as I can find, not a lot out there, if you know of any please post them, only looking for vids, not stills, unless they're the result of the vid as below.

thanks, Brian

​​​​​​https://www.flickr.com/photos/bohemi...n/photostream/

here's what it looks like:
​​​​​​

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Old 02-06-20, 03:37 PM
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Tom Ritchey showing how he fillet brazes at the Bicycle Academy. Fast forward to the 11th minute if you want to skip all the fluff.

https://vimeo.com/199989821
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Old 02-06-20, 04:10 PM
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that was interesting, I'm impressed he still feels confident enough in his brazing to do it in public. Main takeaway I have is that he switches sides so his big fillets don't collapse. I have had that experience doing big fillets, but I only did that for fun, I'm a "small fillet guy" as he says.
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Old 02-07-20, 06:01 PM
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Originally Posted by calstar
David Bohm on Flicker, moves the torch a minimal amount, great heat control(understatement), probably just moving the puddle along with complete control while dipping the rod in. He filmed this in a timed speed contest/bet against another builder tig welding a joint, most likely takes a little more time but who knows.I'm posting as many vids of fillet brazing as I can find, not a lot out there, if you know of any please post them, only looking for vids, not stills, unless they're the result of the vid as below.

thanks, Brian

​​​​​​https://www.flickr.com/photos/bohemi...n/photostream/

here's what it looks like:
​​​​​​
Dave is truly a master at his craft! That's where I used his gas fluxer.
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Old 02-08-20, 02:51 PM
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If anyone wants a Gasflux in line fluxer (#69) PM me. I've not used mine since I had the company do a clean and regasketing. Andy
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Old 02-08-20, 05:58 PM
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Toyo:

​​​​​​

Big rod, looks like 5/32 or 3/16. Also notice he smooths out the fillet with the flame after laying it down. In one part(47 seconds in) it looks like he builds up the brass then pushes the mass along to form it without adding any additional filler.
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Old 02-09-20, 07:12 AM
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I always thought it would be nice to put my spare pare of didymium glasses on a camera and take a video of brazing
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Old 02-09-20, 12:05 PM
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Originally Posted by unterhausen
I always thought it would be nice to put my spare pare of didymium glasses on a camera and take a video of brazing
Years ago when my first wife was still here she looked into this via her photography view. She found a camera lens filter claiming to do what didymium does for your eyes but the film. She would have used it on her Leica. But that was way before the interweb and digital stuff. I suspect that such a lens is still available, I never bothered to remember what kind it was.

Somewhat unrelated but still imaging a torch is this holiday card she and I did about 15 years ago. Andy
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Old 02-09-20, 12:09 PM
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Originally Posted by Andrew R Stewart
excellent!
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Old 02-09-20, 05:01 PM
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OT but this is the best a quick google could find, $85, don't know if they work as advertised but it would be great if it did.

"We are pleased to present our line of sodium flare camera filters for SLR/DLR cameras and cellphone/pad/laptop cameras (available in a clip-on form)".ttp://www.auralens.net/en/camera-filters

​​​
Only review FWIW:
"I spent forever looking for this type of camera filter; all I could find were filters designed for color enhancement with far less metal in the glass than needed for photographing glass lampwork. This filter is perfect for that, plenty of didymium in the glass."
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Old 02-11-20, 11:54 AM
  #37  
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My pratice fillet brazing "tool"

“The advantage of having a long tube is that it serves as a handle to keep constantly moving the joint to the best angle for fillet brazing. Of course to do this your tube holder has to be tightened to that sweet spot between tight/free where it will move without much effort with your non-torch hand but will stay put when it is in the right position without having to adjust the vise handle.” Doug Fattic

This is a great suggestion, I’ve modified the concept a bit so I can get a lot of practice pieces, 18-20, on a relatively short length, the entire tube can be used, no end waste. Using this method keeps from having to turn/touch(or having my Park work stand holder's rubber surface start to melt)a hot tube which I found to be the case if I wanted to do more than just one at a time. The "tool" tube( 20"+-) is held by my work stand, loose enough so I can rotate it. Sort of a long winded explanation so I added the pics for easier understanding. This is not an original idea, I caught a glimpse of a similar “tool” on Brian Chapman’s instagram site, he uses it for rotating stems he builds.

Here's what I do, takes only a few minutes and an old vise-grip:

Remove the adjusting screw from the vise grips, fit and weld/braze it into a tube(I used an old junk bike down tube) keeping the axis of the screw as parallel as possible with the tube axis. Add a lock nut before installing the tube/screw, keeps the vise grip from loosening while rotating it, adjust the tension of the grip jaws the same as you would a vise grip, just turn/screw the tube.

Braze a mitered piece onto the center of a length(2’ is good) of tube(whatever diameter you want to attach the mitered stubs on) about the middle of the length, this is the piece/stub the grip will hold, maybe using a little longer stub. All brazing practice miter pieces are brazed on perpendicular to the originally centered brazed on stub. I use two rows 180* from each other, spacing the stubs 2.5” apart, when brazing on the opposite side center the pieces between the stubs above.

I usually braze 2-3 stubs(on any given day) on the same side, then soak and clean the flux before brazing more 180* during the next practice session, this keeps the melted flux from interfering with the fit of the miters on the pieces 180* in the same area.





I obviously braze on the other/farther end of tube, not close to the work stand as shown here
​​​​​​


​​​​​​
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Old 02-29-20, 02:44 PM
  #38  
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practice makes better

I'm learning everytime I pick up the torch, trying different tip size, rod size, flame proximity to work, torch angle, brass flow rate, etc.

​​​​​​
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Old 02-29-20, 07:43 PM
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that last picture is awesome
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Old 03-13-20, 07:30 PM
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pneumatic fillet finishing

Toyo, looks like they hardly need finishing

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Old 03-14-20, 01:44 AM
  #41  
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Originally Posted by calstar
Toyo, looks like they hardly need finishing

​​​​​​https://www.youtube.com/watch?v=4EoMaWOftdc
Yes, those are some really nice looking fillets. I'd finish those with only hand sanding, if the budget allows it.

The tool he uses is really dangerous in the wrong hands though. I didn't see him making any deep troughs, but using that tool without digging trenches in the tubing adjacent to the fillet takes a lot of skill. Even so, I can guarantee that he has thinned the steel a little there, at least a little. I'd still ride that bike though because (a) the video shows mastery and (b) it's probably not super thin tubing.

A lot of beginners think they're good enough to get away with a tool like that, but their eye is not finely attuned enough to see the damage they're doing. I have often seen a deepish trough around the fillets after a framebuilder got a dynafile. Even after paint. (I could name a few but you wouldn't recognize the names -- those guys didn't last long in the biz.) "Whoo-eee, this thing is really fast!" Yeah -- too fast. So, my advice is: learn on thick tubing, like 1.0 mm or thicker, and hone your technique for a year or three before you even think about doing that on thin stuff. If you want to fillet-braze on 0.7 or thinner, best to braze 'em clean and not smooth the fillets at all. Maybe a bit of manual shoe-shining with 1" wide "utility roll" (abrasive cloth strip). But even that can thin the steel, so use judiciously. Skip the 60 grit; even 80 grit is for masters only. Start with 120 grit precisely because it's slow, so you'll have more time to see the damage you're doing.

Remember, when you touch the steel at all, you're thinning it at the worst possible place, where bending leverage is at a max and strength is at a minimum, due to the tempered zone around the braze. You see those factory built bikes, like from Toyo, or a Crust Lightning Bolt, and assume you can do that or better because you're an artisan. But some of those factory guys have been doing it for 10 years, long hours and every day. Even more importantly, they learned under the watchful eye of a master, who slapped them whenever they did something sub-par. Your average one-man shop, a guy who took a UBI course and calls himself a Master Framebuilder, will never get that good as long as he lives. He skipped the apprenticeship.

Any consumers reading this? Thinking of a custom frame? Don't trust your eyes; you have to be trained to see the damage, and so you won't. Don't trust the builder's spiel (or website), because he might have honed that more than his skills. His track record and reputation is about all you have to go on, and I'd like to see at least ten years of being a known quantity. There are a very few guys who come out of the gate making really nice bikes (Mitch Prior, Chris Bishop, Brian Chapman et al.) but those guys are unicorns. Builders who have achieved mastery the old-fashioned way are rare in this country nowadays because they're dying off (Baylis, Gordon, Della Santa) and not being replaced -- there's no pipeline. A two-week course is not an apprenticeship.

So scrutinize the builder's track record and reputation -- and make sure he has product liability insurance!

Mark B in Seattle
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Old 03-14-20, 03:23 AM
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Just read this excellent advice after attempting this braze-sanding thing for the first time as a total rank amateur and using a dynafile Below is a mercifully slightly out-of-focus picture. These are actually cosmetic TIG brazes over the top of TIG welds (that I have a lot of confidence in). The upper segments are made of offcuts from the steerer tube and are 2.4mm wall CroMo. The fork blades are 0.9mm CrMo. I was very careful to only touch the bronze bits with the sander except for the very last bit of blending at the edges. I found it helps to use the bit of the belt that doesn't have a platen under it and to hold the edge that you're blending with the steel side towards you. The fork isn't finished yet-- it needs the crown race seat and some cantilever bosses (which I think I'll just TIG weld).



TIG welded and brazed fork
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Old 03-15-20, 12:20 AM
  #43  
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Originally Posted by bulgie
The tool he uses is really dangerous in the wrong hands though. I didn't see him making any deep troughs, but using that tool without digging trenches in the tubing adjacent to the fillet takes a lot of skill. Even so, I can guarantee that he has thinned the steel a little there, at least a little.
It's also good reason to dish out a few extra bucks on 631 (or 853 etc) tubes, expert or not, when making big fillets. It's not just that the steel is stronger against breakage, but that the steel is also harder and a bit more abrasion resistant post-brazing. I'd also steer away from the fancy grinding belts.
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Old 03-15-20, 01:41 AM
  #44  
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Originally Posted by Kuromori
It's also good reason to dish out a few extra bucks on 631 (or 853 etc) tubes, expert or not, when making big fillets. It's not just that the steel is stronger against breakage, but that the steel is also harder and a bit more abrasion resistant post-brazing. I'd also steer away from the fancy grinding belts.
Huh, hadn't thought about that, but it makes sense.

I made some lugless Aermet 100 Alloy frames (precursor similar to 953), and that stuff was noticeably hard to scratch.
Made a bunch of 853 frames too, but they were lugged, so I never had the experience of cleaning up fillets on 853.

Yes the added hardness is working in your favor when it comes to not digging trenches around the fillets, but it's still not an excuse to use a dynafile on thin tubing. IMHO. I dynafiled miles of fillets (maybe literally?) when I was making tandems all the time, but I stopped when tube walls got thinner (and coincidentally my fillets got smoother, less need for power tools). I'm not saying you can't use that tool, if you're very good and careful. I'm just saying a lot of guys think they're good enough but they're not.

Dynafile owners probably know this already, but they make a contact arm that is all unsupported belt (#11219). And 1/8" wide belts exist, much less likely to dig in the edge than 1/4" belts. But I still recommend people avoid them for very thin tubing. Even if you're trying to feed your kids -- make shortcuts somewhere else!

Mark B
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Old 03-15-20, 10:02 AM
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I think a dynafile would make short work of 853. Filing fillets is why you have thumbnails, to keep the file on the brass
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Old 03-15-20, 10:56 AM
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Good abrasives can make short of any steel if you try, that's not really the point. The point was that air hardening steels are particularly well suited for dealing with undercutting issues, dynafile or not, thinwall or not, novice or not.
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Old 03-15-20, 08:05 PM
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Originally Posted by Kuromori
Good abrasives can make short of any steel if you try, that's not really the point. The point was that air hardening steels are particularly well suited for dealing with undercutting issues, dynafile or not, thinwall or not, novice or not.
Yes, wherever you are on the ham-fisted to godlike skill spectrum, all else equal, steel with higher surface hardness should be safer against thinning the wall locally while sanding the fillets. OTOH those tubes tend to start out thinner too though, so even a little thinning is a higher percentage of the total thickness lost to make the fillets look pretty.

I think we can all agree that no matter how good you are, smoothing the fillets to make the edges disappear will inevitably thin the steel, at least a little. No one can keep the abrasive or other tools 100% away from the steel, unless the edges are left visible. As I guy who's cleaned up a lot of fillets, I'm not saying Don't Do It, just consider keeping it to a minimum. Maybe let your painter do some of it, with sanding the primer or even a little painter's putty. No shame in that if it makes for a better, longer-lasting frame.

Sorry if that's too obvious to bear mentioning. I think we have some beginners or less highly trained amateurs here though, who could do with a little reminder. Just the other day I saw an older frame from a well-known builder where the dynafile trough around the fillet was visible (to me) from 5 feet away. I tried to show it to the bike shop dude I was talking to but he couldn't see it. The signs are subtle. I've seen it in an Alex Singer handlebar stem too, which didn't worry me much because I'm sure it's very thick tubing. Made me wonder if stem filing was one of the jobs given to apprentices BITD. My old boss, owned a bike shop, 50+ years of looking at nice bikes, but couldn't see it in this stem:


Can you see it in this picture? Blown up from an eBay auction photo.
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Old 03-16-20, 05:27 AM
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A lot of Treks I made had undercutting on the stay ends because the guys with the dynafiles could get a little ham-handed. Ignoring the potential structural problem, I think it looks like crap. I was always a bit pissed about that. My goal for fillets is to not have an edge and avoid this problem altogether.
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Old 03-16-20, 08:59 PM
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Originally Posted by unterhausen
My goal for fillets is to not have an edge and avoid this problem altogether.
I think I know what you mean, but for the sake of people reading this to learn -- you mean brazing them so the toe or edge of the fillet feathers out into the steel? Hard to describe in words, but it's a fillet that doesn't need any metal removal to look good painted. When everything is just right -- prep, flux, heat distribution, flame size and position etc. -- the fillet wants to make this shape. It just lays down that way. Beautiful to see while its happening.

I noticed that a titanium weld puddle does that too. Never could get a steel weld to make that shape, or at least not nearly as perfectly as Ti did, right from my first attempt at welding Ti. (I had a good teacher.) It's more like brass fillet brazing, which I was good at already by the time I learned to weld Ti. Similar enough to the muscle memory from fillet brazing, that making that shape in Ti was easy. The fact that I thought the Ti weld puddle was beautiful to look at molten, before it froze, had zero benefit to the consumer, who never got to see that. But it did make me like welding it.

OK, I digress (as usual). But it does pertain to this discussion in a way, because with Ti you don't usually get to smooth the welds or even hide them under paint. If you try to get your fillet brazing to that same standard, fillets that need no smoothing or hiding, then your frame will probably last longer. And think of all the time you'll save compared to sculpting and smoothing all your fillets. Even with die grinders and dynafiles, it's still a lot of work that can be avoided with fillets laid down right to begin with.

Mark B
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Old 03-16-20, 10:48 PM
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Originally Posted by bulgie
Yes, wherever you are on the ham-fisted to godlike skill spectrum, all else equal, steel with higher surface hardness should be safer against thinning the wall locally while sanding the fillets. OTOH those tubes tend to start out thinner too though, so even a little thinning is a higher percentage of the total thickness lost to make the fillets look pretty.

I think we can all agree that no matter how good you are, smoothing the fillets to make the edges disappear will inevitably thin the steel, at least a little. No one can keep the abrasive or other tools 100% away from the steel, unless the edges are left visible. As I guy who's cleaned up a lot of fillets, I'm not saying Don't Do It, just consider keeping it to a minimum. Maybe let your painter do some of it, with sanding the primer or even a little painter's putty. No shame in that if it makes for a better, longer-lasting frame.
I think 631 is one of the only steels still being made in 1/7/1 but I don't think they're all stocked here and the 25.4 top tube is limited to 8/5/8.

Even though big fillets are mostly for aesthetic reasons, I think most customers draw the line when it switches over from functional craftsmanship with an artistic flair to pure and unnecessary aesthetics. I do think bondo fillets would probably result in a stronger frame due to heat issues. Yet another reason for 631/853, as I don't think you can realistically or safely hit the hardening window for 4130 with the way a big fillet is done, even if you do fully wet out the filler and don't touch it. But no customer is ever going to be happy with bondo fillets any more than a customer would be happy if you glued some fake plastic lugs on before painting.

It does remind me of a stripped Jo Routens frame I saw pictures of though. Jo Routens tended to use very small fillets except at the headtube. Anyways, this one had some kind of silver-gray filler, the owner said it was gas welded. I couldn't help but wonder if it filled in with some low temperature solder like they used to do for auto dent repair. Much lower temperature and it's actually shaped with wooden tools instead of just being allowed to flow.
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