I have aspirations of building a lugged steel frame and I’ve been practicing silver brazing for a couple weeks now to prepare. I’ve been referencing the book ‘Lugged Bicycle Frame Construction’ by Marc-Andre Chimonas. This book recommends practicing by splitting sections of tube and fitting them over the same tube to simulate lugs. Basic competency is described as “fully penetrating the mock-lugged joint with brazing alloy without exhausting your flux.” I am able to get penetration but I am unable to complete a joint without exhausting flux somewhere on the part. I don’t know anyone to ask for help in person so I’m hoping to get some direction and criticism here. I’ve included a video of me brazing.
My equipment, as recommended by the book:
Harris SSWF1/4 Stay Silv Brazing Flux
Harris 4531 Safety Silv 45 Silver Brazing Alloy
Benzomatic map pro torch
Video of me brazing:
As the video shows, the flux starts to exhaust shortly after my first application of braze. I appreciate any feedback.
too much general heat. You need to focus the heat more on the area of the workpiece you want the filler to go. This may be difficult to control with a map torch as it’s a much broader flame than a brazing torch.
from what I understand you want the silver to wet in between the tube and the plate like a lug. So in this case, what you really want to happen is the underside/inside of that top plate to come up to wetting temp. You have to think about getting the heat through that plate to the underside so when you feed filler at the joint/“shoreline”, it pulls in between the tube faces. You should be concentrating most of your heat on your lug piece so that inner face comes up to temp. Some heat on the underside of the tube under the lug can help this too but you should mostly be heating the lug.
too much filler that’s too cold: especially with silver it’s easier to manage small amounts of filler at a time and add more as you need. If you add too much of a blob at first and the piece is too cold, it’s just going to blob or eventually puddle away from you with a mind of its own. It’s much easier to control a small amount of filler at a time, put it where you want it, and then top up a bit at a time as necessary. You can see this around 2:58 you have more than enough filler there for that whole plate but it’s just piling up on the edge of the joint - adding more filler at this time is only going to be difficult to control. The solution is more heat, not more filler. It kind of starts to get there at 3:11 but then you move the heat away from that area.
you are trying to “push” the silver where you want it to go as opposed to “pulling” it in with the heat. When brazing, especially with silver, think of adding heat where you want the filler to go instead of adding heat to the filler. If you get where you want to join up to temp, the filler will go there. It requires very little heat on the actual filler to move it. 3:19 you are heating the silver puddle and trying to “push” it under the lug. Approach this in the opposite order - heat the lug and only slightly wick your flame up over the joint to “pull” the filler in between faces. If you are trying to heat a pile of silver to move it without giving it somewhere to land, it will likely just completely wet away from you or burn.
gravity: use gravity to your advantage whenever possible silver brazing (or brazing in general). Turn the workpiece vertical and feed filler in at the top edge of the joint and use your heat to pull it completely through the face of the joint. If you are practicing, drill a few holes in your plate at different distances from the edge, and when you are adding filler on from the top edge and pulling it, you should see it wetting out of the drill holes without having added any silver there. This indicates full joint penetration of the silver between the faces.
Lots to think about. Hope that helps, keep practicing!
Also consider that your c-clamp is acting like a heat sink and wicking heat away from where you need it.
Using something like a grasshopper would be better than a c-lamp. I’ve made my own my bending the handle of an old file and placing a welding magnet far away from the flame.
There are two videos I can think of that might help:
thank you for all this information. This is very helpful. I will try to apply this all the next time I practice. I also have plans to invest in an oxy fuel setup at some point so it sounds like that should make things easier.
I’m no expert, but I always thought the recommended silver filler for lugs is 56%, not 45%. I think the 56% is more “runny” at temp. I don’t know if this matters – people do join lugs with bronze, which is (I think) harder to flow than any silver.
What everyone has said so far is all great advice. I want to reiterate the bit about where to heat: You need to heat where you want the silver to go, not where you add it. When the joint is up to temperature and you add filler, it will just suck right in - not pool up on the edge. If it does freeze on the edge, move the heat to the middle of the two plates and work the heat back toward the edge. The steel is what needs to melt the filler, not the flame.
Watch your video again and take note of how much heat you are putting into the tube towards the left side of the screen (where no brazing will occur) and how little heat you are putting into the braze area, especially the far right edge where it’s clamped. The flux is still white around the right edge of the joint, meaning it’s nowhere near up to temp. Since it was hotter on the edge than in the rest of the joint, there was no chance the filler would wick into the joint.
I agree that the clamp is not doing you any favors. Try tacking two ends and then remove the clamp completely. The part could move around if you get the whole area up to liquidus, but realistically some of it will probably always be frozen. Plus, gravity holds stuff pretty well. I do all my cable/hose guides without clamps.
I also agree you should try 56%. It wicks really well into tight gaps and melts at a lower temp. It will help you learn how the filler moves. 45% is better for looser gaps and building up small fillets.
Yes, watch the Paul Brodie videos. Also check out Chapman Cycles on instagram. Brian is a master and has incredibly filmed and edited bite-size process videos. Some are so close up that you can really see the way the silver moves when hot and how it pools and freezes. This forum is also an excellent resource so thanks for asking questions! I have been brazing for ten years, but I’m still asking questions on here. Keep practicing.
Just this afternoon I bought an oxyacetylene kit from facebook marketplace. Once I’m comfortable with the new torch and I’ve applied all the new info I’ve gotten from this thread I’ll post another vid.
On Thursday I got an oxyacetylene kit and I’ve been practicing with it since. I haven’t made as much progress as I would like but I told myself I would post a video today so here it is.
Just watching it myself it’s clear that I’m putting too much heat into the front part of the ‘lug’. I wasn’t aware of this during the process. I’m struggling with knowing when the part is hot enough to melt the braze. I can get the flux translucent but there’s still a margin between translucent flux and brazing temp, and then it seems like there’s another thin margin between brazing temp and flux burning. Assessing this by myself, I feel like I need to more often flick the flame off the part the closer I get to the brazing temp.
Also, sometimes the braze wicks on top of the lug instead of under it. I’m not sure how to stop that. Could it be possible that there is too large a gap between my lug and tube for capillary action since I’m not using a clamp?
Thanks for the help. This is still the 45% but my 56% silver is in the mail.
First things first, you gotta turn down that torch! With it hissing like that it’s gonna nuke your steel before you have a chance to blink
Go to YouTube and search for Paul Brodie’s brazing videos. Take a look at setting up the flame properly for silver soldering. Watch those videos all the way through, then watch them again.
If you have extra cash to spare, look at purchasing a Miller/Smith AW1A, a set of lightweight hoses from TinMan, and a few tips.
I had a really hard time using a large torch with heavy hoses while developing an “ok” technique. Doug Fattic suggested a smaller/lighter set-up and it helped tons. The downside is that a small torch gets hot if you’re brazing a lot.
Haha yeah. I’ve watched paul brodies videos. He says if the acetylene only flame is smoking then turn it up. That was the smallest clean burning flame i could get. Does that mean my tip is too big?
I’ll second the recommendation to get a Smith AW1a and some lightweight hoses. For the Smith I use a 205 tip for pretty much everything and a 201 for little braze-ons, but really the 205 can do the small stuff too.
The Smith does get hot to the touch during a long brazing session, but it’s tolerable if you keep your hand choked down near the hose connections.
If you can’t afford a new torch post what your current torch is and what the tip size is. Someone here might be able to suggest an appropriate tip for you.
I can afford to put a little money into this hobby but I want to develop skills before dropping big bucks. My current torch is Harris with a #5 tip. I’ve already ordered a #3 tip and it looks like it will be compatible with what I have. If that’s still too big I’ll try a 2 or a 1. Looking at other threads though it looks #3 is a common tip size for framebuilders and it’s similar to the 205 that manzanitacycles recomended.
FWIW, the tip we used in the UBI framebuilding class was a Victor #0, which is 0.035". It looks like the Harris #5 tip is nearly 2x as big at .060". You might try dropping to a Harris #2 tip, which is .035".
Also we were taught to use a reducing flame for silvered lugs – presumably because it’s slightly cooler and less likely to scorch the tubes?
All of the advice here is solid. Brazing sleeves like this is a good way to simulate lugs.
A couple things I don’t see mentioned:
The clearance for 56% silver needs to be pretty small. For brass/bronze the gaps can be much bigger. 45% silver is much too gummy to flow into a lug/sleeve. 45% is good for filling tabbed dropouts or other big gaps. I think in the welding tips and tricks video he mentions the clearance but generally you are shooting for 0.002-0.004" gap (half of clearance). That’s pretty snug as the tubes aren’t perfectly round. If you’re using for example, 1" tube with 1-1/8" .058" walled tube for your sleeve, you end up with like a .009 clearance before you clean up the inside and outside of the tubes. This is at the bigger end of the range that I found to work best. The snug fit helps in 2 ways:
capillary action - 56% when melted is quite thin and wicks best into small gaps
heat transfer to the inner tube - If the inner tube isn’t at temp, the silver will flow to the outside of the joint and make a mess and waste filler.
Using .065" walled sleeve and turning or grinding 5-6 thousandths out will provide the clearance you’re after. I did a bunch of testing at one point and the sleeve should require a little force to spin on the tube. I have heard some will take a course round file and run it through the sleeve longitudinally before brazing to create small channels to help the filler flow.
Get some SS flux from Cycle Design. It has a higher heat range which will buy you some time before it is exhausted. And I know Paul says you don’t need much, and I agree, but when you’re just learning, a little extra doesn’t hurt. I typically put it a little up the tube so I can scoop it up and move it around with the filler rod.
For lugs, crowns and other big items, I typically use a bigger tip (Victor #2 or the biggest propane tip Paige Tools makes) at low (~5psi) pressure. This allows me to get the joint hot faster and I can keep the whole joint at temperature so the filler transfers throughout the whole joint.
Hi again. I’m back. I bought a Harris 1,2,and 3 tip and some 56% silver braze.
With a smaller tip I definitely feel like I have more control over the heat. However, I’m still burning flux and I still can’t fully penetrate a joint reliably.
I’m flicking the torch away periodically to try and stop hot spots but I just feel like this monkey using a hammer. I’m copying the motions, but I don’t fully understand what I’m supposed to be doing.
Anyway, here are two videos. The first one uses a #2 tip and the second one uses a 3. I burn some patches of flux in both videos.
I’m using 1", .049" wall for both sleeves and the main tube. I squeeze the sleeves on with vice grips and the gap is pretty small, but probably not < .009" all the way around. Now it makes sense that I sometimes the braze pools on top of the sleeve rather than underneath.
