Tips/Techniques Feedback on Brazing techniques and results

[Xyphota]

I gave brazing a second go with a much smaller torch and tip. I got my partner to take a video of the process so I hope you guys can give me some feedback.

Materials:
Tubing: 0.6mm thick chromoly (~0.025")
Braze-on bottle boss: ~1mm thick chromoly (0.040")
Filler Metal: Fillet Pro - https://www.cycledesignusa.com/silver/fillet-pro
Flux: Harris Stay-Silv white brazing flux - https://www.harrisproductsgroup.com/en/Products/sswf7

Torch setup:
Tip size: Little torch #5/AW202 (this is almost exactly the same size as a victor #00 -> http://www.bikesmithdesign.com/Welding/tips.html)
Acetylene pressure was 4 psi at the regulator. I opened up the valve on the handle until there was little to no soot coming off the flame.

Below is a photo of the end results, about 15 seconds after turning the torch off.



Self-reflection: I know the blackened charred bits is burnt flux, and that is generally to be avoided LOL. At 1:44 in the video I can see there is 1 spot that got white hot which matches the large blackspot on the lower-left boss in the photo above. I thought the first boss (upper-right in photo) went pretty well, but I was surprised to see some burnt flux after taking off my goggles. The black flux on the upper-right boss is still kind of shiny and glassy, whereas the large burnt sections on the lower-left is dull, and a bit sand-papery. Clearly charred. I've read that other framebuilders use a Victor #00 tip for these small braze-ons (which is essentially what I used here), but the torch in their videos sounds less turbulent, so I wonder if I should just choke up the valves a bit.

Here is a framebuilding master showing how its done. He is using a #0 tip, but his flame sounds much gentler than mine. He is also using a heat sink which also serves to keep the boss level.

I was a bit surprised at how quickly the tubing went from a dull grey to white hot. I held the torch a few inches away waiting for the white flux to activate, then I went in and tried to melt a dab of filler. By the time the filler melted the tubing was overheated.

 

[PeterT]

I was going to suggest Paul's channel. In one of the brazing vids (maybe that's the one) he discusses flux in the gas itself which is if I recall why it has that green glow

 

[Xyphota]

Paul discusses his brazing setup in the first 2-3 minutes of this video:

I actually have a GasFluxer (same thing, different brand from what Paul is using) that I bought from a fellow in Calgary ~2 years ago who is also building some bike frames. I haven't hooked it up yet, but maybe I should LOL.

 

[phaxtris]

It looks to me like your concentrating to much heat on the tube, and not much on the bung, the bung is the bigger heatsink and you should be heating that up more than the tube

I imagine that tube was pretty warped after that ?

 

[Xyphota]

I think you are probably right. Also, after looking at Paul Brodie's technique again, he is pointing his flame at a bit more of an angle relative to the tube, with the flame sort of glancing across the tube, whereas I was pointing the flame more perpendicular to the tube.

I didn't think to check for warpage, I'll check with a straight edge later. I did spend 30 mins filing the excess filler off though so I think I would have noticed it if it was severe.

 

[Rauce]

I hold the torch at a bit more of an angle as well. I also have the flame a lot less aggressive.

I warm the whole area carefully until the flux has all dried then I direct heat at the boss until it’s starting to go a slightly dull red. Introduce filler and then check if it went all the way around. If you get it right you should only have to dab the filler once.

I wear clear safety glasses when I silver braze, otherwise it’s too damn difficult to see subtle colour changes in my experience.

 

[Xyphota]

I checked for warpage with a straight edge and couldn't see anything. I posted this same thread to a bicycle framebuilding forum and my main take-away other than poor technique (LOL) is the torch flame is too aggressive. I took an oxy-acetylene course at SAIT last year which mostly focused on welding, but there was one class of brazing 1/8" coupons together with a flux-coated brazing rod. When setting the torch up, the instruction was to light the acetylene only, then open the acetylene until there is there is little to no soot coming off the flame, and then add the oxygen and get your neutral flame. Maybe this was the rule of thumb for welding, but it seems this setting is much to aggressive for brazing, especially silver brazing. My next attempt will definitely have a much softer flame.

 

[TorontoBuilder]

I concur with the others who say angle the torch.

I have brazed thousands of fittings over the years, especially ones with heat sensitive components. I tend to heat gently at an angle and on the fittings rather than the tube. A fitting tends to have the greater thickness and transfers all the heat required to the thinner tubing. I'll dab the silver solder on the tube when it looks hot enough, and the solder will flow into the gap.

 

[TorontoBuilder]

I checked for warpage with a straight edge and couldn't see anything. I posted this same thread to a bicycle framebuilding forum and my main take-away other than poor technique (LOL) is the torch flame is too aggressive. I took an oxy-acetylene course at SAIT last year which mostly focused on welding, but there was one class of brazing 1/8" coupons together with a flux-coated brazing rod. When setting the torch up, the instruction was to light the acetylene only, then open the acetylene until there is there is little to no soot coming off the flame, and then add the oxygen and get your neutral flame. Maybe this was the rule of thumb for welding, but it seems this setting is much to aggressive for brazing, especially silver brazing. My next attempt will definitely have a much softer flame.

yeah, have seldom even used oxygen for brazing silver solders or various blends. Only mapp gas or plain acetylene and a turbo torch

 

[phaxtris]

When setting the torch up, the instruction was to light the acetylene only, then open the acetylene until there is there is little to no soot coming off the flame, and then add the oxygen and get your neutral flame. Maybe this was the rule of thumb for welding, but it seems this setting is much to aggressive for brazing

they taught you correctly for brazing or welding, just not for brazing .065 tube

they taught you how to set the torch consistently to try and eliminate variables while your learning, you can set the torch lower or higher, but think of the frustration it would be learning how to torch weld/braze when one day you set the torch for 100,000btu, and the next day only 50,000 btu, it would be an uphill battle for sure!


just a suggestion, take it as you will, i think you should take a chunk on that pipe, and make a bunch of dummy bungs, approx the same size round bar with a hole punched in the middle so it has roughly the same thermal mass, and just practice brazing them on, you could braze on 10 or 20 "bungs" in the same piece of tube before you try it on the real thing. Doing something like that wouldn't really be out of the ordinary at all

 

[Xyphota]

*0.025" tube

I agree, that is a great idea. When I purchased my tubesets, I accidentally purchased the wrong seat tube so now I have an extra one that I could probably sacrifice to put 30 or 40 dummy bosses on. The tube is intended to be used for lugged construction which I'm not really interested in so I'll probably never use it otherwise.

 

[phaxtris]

*0.025" tube

I agree, that is a great idea. When I purchased my tubesets, I accidentally purchased the wrong seat tube so now I have an extra one that I could probably sacrifice to put 30 or 40 dummy bosses on. The tube is intended to be used for lugged construction which I'm not really interested in so I'll probably never use it otherwise.

oh boy, i would for sure be making some test pieces !

 

[Rauce]

*0.025" tube

I agree, that is a great idea. When I purchased my tubesets, I accidentally purchased the wrong seat tube so now I have an extra one that I could probably sacrifice to put 30 or 40 dummy bosses on. The tube is intended to be used for lugged construction which I'm not really interested in so I'll probably never use it otherwise.

You can still use old school single butted seattubes, just have to add a sleeve. I’ve done it a few times to use up tubes that I have on hand. 1-1/4 .058” wall sleeved over the top or turned down slightly to save a little weight.

 

[Xyphota]

I just checked spruce aircraft, and their 1" x 0.028" tubing is $40/foot, so it would actually be cheaper for me to sacrifice this seat tube LOL.

 

[TorontoBuilder]

I just checked spruce aircraft, and their 1" x 0.028" tubing is $40/foot, so it would actually be cheaper for me to sacrifice this seat tube LOL.

where are you purchasing your butted tubes? I assume you're using butted tubes anyway... I need to start planning to buy tube for my project

 

[Xyphota]

I should add that most of the tubing above 0.035" at spruce aircraft is more reasonably priced.

where are you purchasing your butted tubes?

If you look at my bicycle projects thread, the recent posts are about tubing vendors.

 

[Xyphota]

Here is some brass brazing practice. I purchased some tinted glass-blowing glasses which made seeing the colour of the metal much easier. Do you guys have any recommendations as to how to avoid bubbles?

EDIT: This is 1/2" x 0.028" chromoly tubing brazed to 3/16" chromoly plate. The flux used is GasFlux type B in paste form, and the filler rod is GasFlux C-04 rod. They call it a nickle bronze rod, but I think it is technically brass because it has zinc in it??

 

[phaxtris]

Either it wasn't clean enough or you overheated it and burnt the zinc out

 

[Rauce]

Too much heat can definitely cause bubbles, especially the smaller pinhole type ones. One tell tale sign of overheating is areas of the filler appearing more copper coloured.

I think that’s more than good enough though. I’ve done several dropout swaps and repairs on old frames where there was probably 10-20% of the filler you’ve got in there and they held up for decades and weren’t even the part that failed.

A good tip for slotted stays is to round the corners on the slot, a sharp corner there even once it’s filled in with bronze can start a crack.

 

[Xyphota]

Either it wasn't clean enough or you overheated it and burnt the zinc out

It didn't even occur to me that the bubbles could be from the brass itself. Very interesting.

Too much heat can definitely cause bubbles, especially the smaller pinhole type ones. One tell tale sign of overheating is areas of the filler appearing more copper coloured.

The outside looks a bit copper coloured to me, would you say this looks like it was overheated?

A good tip for slotted stays is to round the corners on the slot, a sharp corner there even once it’s filled in with bronze can start a crack.

Thanks for the tip. Do you try to file a radius into the dropout to match?