Thankfully it's not too often that something goes wrong to a point that might be the end for that particular piece. Yesterday I was trying to braze on a SS cross to the top plate of a dual plate crown's fork. I have been working on 8 forks for Doug Fattic's Ukraine Project and am most of the way through them. It was time to attach the little crosses (the project is to provide transportation bicycles to members to encourage community outreach, my words, so the crosses are a small visual reminder as well as a marker of a religious purpose. Also helps IDing the bikes if any were to be stolen). They are a precut stainless steel piece.

I have worked with SS before and never got really comfy brazing it. (My own bikes use a SS "S" as a head tube badge and I've done some SS dropouts and S&S couplers). My problem has mostly been heat control, the SS slow heat dissipation and flux cook off. For the flux, at Doug's workshop, GasFlux type G was used (a silver intended flux with a slightly higher temp range than their more common type U).

Back home I tried the G flux, cleaned the cross bottom and crown top applied the G flux, positioned the cross with and held it in place with a sprung pointer/rod from above. At this point the forks getting the crosses had been otherwise completed and the blade vent holes plugged, this last bit is an important detail... I had all sorts of difficulty getting the silver (50N) to flow under the cross. I heated the top plate's underside a bit and as the plate got close to temp I moved the torch to the top side and worked the flame around the cross, directing at the plate initially. When the flux looked right I added silver to the plate right at the cross edge. The silver would wet out on the plate well and also wet to the cross's top surface (not what I wanted but I could file/sand that away after) but not penetrate under the cross to any significant degree. Seeing this I quickly removed the cross and let the fork cool for flux soaking off. When cool it went into my heated water soak tub.

I repeated this for a second attempt on a second fork. Pretty much the same but with a very little penetration. Again I removed the cross when all was still hot. I took fork 1 and filed/sanded down the silver left behind and decided to try type G flux and 56% silver as I am more at ease with them. This time I did get what I think is sufficient penetration but the cross turned out slightly crooked. Cool off and back into the soaking tub. The next effort had me trying to wet out some silver on the plate before placing the cross but the wetting out layer didn't go well so I just stopped.

I decided to remove the sort of brazed cross that was crooked. The heating took more time than the initial brazing did, I had to focus the flame directly on the cross and finally began to see the silver start to melt but before the cross detached this happened.


There was a sort of explosion as the top plate was blown off the blade's top, loud enough for the wife to hear it outside of the house... My right ear is still "off", I might have injured the eardrum. Thankfully a day later my ear seems to be slowly getting better but I bet I did more harm than all the Greatful Dead concerts I attended as a young one have done. With a closed blade the air pressure increased A LOT and with the silvered plate to blade joint likely weakened/softened by the heat of removal the top plate "popped off". Check out this shot of the fork on my cutting matt. I lined the steerer up with a line and placed a grey nail piece (what I plug vents with) along the steerer's center line where the dropouts should be equally distant from.


You can see a few deformations besides the top plate's one side. The lower plate on that side is also bent a bit and the blades are now askew to one side. In this next shot you can see that the brazing of the top plate onto the blade had good penetration. The silver is all around the blade end and the top plate's recessed pocket.


Beside this being a deal killer for this fork (I suppose I could remove the crown from the steerer and blades... not sure I want to send out a rebuilt fork though) the blow off was quite frightening for a moment, but as soon as I could think I saw what happened and started to be concerned about my hearing. My day working this project stopped and I spent the rest of the day in a weird funk. I needed some time away to reset (and I'm not there yet).

This was the frosting on the cake of a day that went from poor to bad. A day before I had received my Flu and Covid vaccinations and the sore arms and sort of flu like feelings were in full force. I wasn't eating well that day so was feeling a bit hungry and not at my sharpest (obviously). My take away is to not do frame work when not feeling good. Of course there's more lessons to learn.

One might be to do what I usually do when layering brazings on top of previous ones, use brass/bronze for the first one. Which in this case would have been the blades in crown. While brass/bronze is no stronger than silver its higher melt temp would have kept the blade/plate joining from softening up. Another might be to only focus the cross removing flame directly on the cross and with a large flame to get the cross to heat up quickly, all of my other part removals have been large items like dropouts and fork crowns that needed a lot of surface hot. But the BIGGEST lesson is to not plug vents till all other torch work is done. I never thought that the top plate could blow off so never considered the vent plugging stage as being too important.

This event is the most scary I've had with a torch (including when I lit my sleeve end on fire because of an acetylene leak at the valve). Certainly the most injurious event, as before I only suffered the stupidity burns. I'll get back to the remaining forks soon. I have one more plan I want to try before I completely call the SS parts quits. But I'll drill a vent hole first. Thankfully I can still live and learn more (and hear nearly normally too).

Here on this forum, and most all others, we don't see the mistakes or bad stuff. No wonder as no one wants to be known for their errors. But as soon as I could gather my wits I knew I needed to share what happened. I doubt many others will duplicate the circumstances that led to my event but unlike the sad political trend to not pay attention to and help out others I can't do that. So please take this as a story to avoid and not to mock. Andy

Thanks for sharing that. I thoroughly agree you should not work when tired or feeling off because that's when mistakes happen. Although perhaps not to blame in this particular instance. Yes, you always need vents. I TIG everything and it's also important there that there is a path out. It doesn't turn your work piece into a pipe bomb (fortunately) but the gases explode upwards from inside the tube and blow a messy hole in your weld. A mistake I have made a few times and it's easy to forget.

Glad your hearing is getting better and I hope you make a full recovery. You must have been very shaken!

Yikes!!
As I started reading the first thought that came to mind was "vent hole".
Glad you are ok!

Likely that the top crown plate was heated enough to make the steel plate material more malleable and thus allowed it to bend so dramatically when the pressure finally blew?

Perhaps but there was zero color change. Given the splatting about and rough surfaces of the silver my thoughts are it got soft and was the main "failure" (other than myself).

I cleaned up my shop yesterday and discovered that I had left the soak tank heating coil (a "bucket heater" as found on farms) powered. The water had slowly evaporated, exposing the heater's hot portion and it burned out. A new replacement is now $65 plus shipping. But finally some good Karma, today's Facebook Marketplace had one new in box offered for $20. It is exactly the same model as the old one. Andy

Wow, interesting!! Lesson here is that vent holes get plugged as the VERY last step! Thanks for sharing!

Let's see what lessons there may be in Andy's adventures. He is making these forks just out of goodness. They will be heading to Ukraine to be united with the fillet brazed frames already made by Tim and Yuriy in Bucha Ukraine (google that city if you can stand reading about horrible badness). Some years ago I told a children's story in church. My daughter was about 7 at the time and when they came to sit in the front she sat as far away from me as she could. She was used to her mom leading up front but not her dad and she wanted to pretend she didn't know me if I messed up. As background children's stories often follow a patten of little Johnny or Suzy did something good and as a result, something good happened to them in return. But of course in the real world that isn't often true. My story involved driving east on the toll road when it began to snow with freezing rain. My wipers wren't doing their job so I stopped at a variety store to get some new ones. I was delighted when I went into the store (an Andersons near Toledo) and wipers were on sale! Great! As I was starting to make my selection I see an old guy needing some new ones too looking confused. Sensing his need for help, I asked if he needed assistance. Oh please he said. Of course you know what comes next. He had no idea how to put them on. So in the freezing snow/rain I take my gloves off the put them on. This is a job I truly hate because I never know which of the serval ways the wipers come off and how to put new ones back on. Anyway some time later freezing cold I come back into the store to get my wipers and the sale sign is gone! My sob story of helping didn't move the manager at all to honor their old sale price. He told me I should have bought them when they were on sale (a half hour ago), Good to know now. The situation was so funny I actually didn't get mad. The moral of the story of course is that we do good things for others because we get satisfaction from that and not for a return. So Andy thanks for your help and I'm sorry for the punishment you got in return. The reality is my friends in Ukraine really are suffering in so many ways!

Doug- Yes, I know that my suffering isn't anything compared to too many others.

My story is a bit funnier: When I met my first wife after a first date or two (the first being a bike ride of course) she invited me over for a dinner. Fish, potatoes and vegies. The evening went quite well as it turned out. It was the next date that she said that she had cut her finger and bled into the mashed potatoes. She had been scared that I would react negatively, instead I laughed and suggested it was her love portion and that it was beginning to work. Over the years we joked about this many times.

In this light I consider this event/suffering a form of empathy with the Ukraine effort. A small gift of some of my loss of comfort.

Thanks all for understanding and being OK with my posting this incident. Yesterday I finished the final alignments, chasing and facing, of the 3 good forks remaining in this first batch of 4. This week I'll pick up the torch again to complete the last batch of 4, leaving the vent hole plugging for last Andy.

I'm not trying to add insult to injury, but I've never understood the desire to plug vent holes. I leave them open and use them to spray frame protection inside the tubes.

All my Ukrainian friends are affected in various ways. Yuriy that I have worked with for over 25 years has heart problems related to the stress of war. He wrote me to say he needs a pacemaker but the cardiology hospital in kyiv was hit with a bomb and killed a doctor and nurse. Now he is worried to stay there a week. In fact he worries all the time because he often sees drone or missile bombs overhead. They get wakened up in the middle of the night with air raid sirens so they lack sleep.

The city where the fork crown pieces were laser cut and my fixtures are made has power outages all the time. This means no hot water that comes from the city. Cold showers. They can't take the elevator and be online. Everybody knows someone on the front line they worry about. The towns in Ukraine have women and old men, all the guys are off to war and may never come back. Men that do come home have missing limbs. The company that does the laser cutting has it production greatly reduced and now they have to source steel from Germany rather then Ukraine where the steel mills have been destroyed. The situation is depressing. It is nice to have a project that can help at least a few.

One of the advantages of this group fork building activity is that we can learn from each other. Anyone brazing can pick up bad habits without noticing. It is why pro golfers have coaches. In my framebuilding class manual is a list of common beginner mistakes to watch out for. They include moving your flame hand in as your silver melts. It isn't natural to pull the flame hand back for heat control as the hand holding the brazing rod moves in as it melts. As compensation, one can flick the flame off so the joint doesn't overheat. It is possible that someone might have done this while we brazed forks. I'm not telling.

Brazing stainless steel requires more skill. It has to be cleaned just prior to brazing and its brazing window is smaller but the lower end has to be hotter. When I was brazing the crosses on the top plate, I was careful to not point the flame directly on the cross but traced around it until the plate was hot enough and then added 50N silver (it wets out better with stainless). It is easy to push the cross with the silver so extra care has to be taken. This might include some way to steady the silver hand.

I debated using brass or silver. I'm now going to recommend brazing pieces to the steerer with silver and the blades to the plates with brass. Silver is easier of course. In a production setting a larger flame would braze all of them together at once with brass. It is much easier for an occasional builder to separate the tasks. As a reminder, we used a G-tec #3 TEN tip. It is like a rosebud except with a sharp and longer center flame.

When I drill vent holes, I use a 1/16" cobalt bit. When absolutely everything else involving brazing is done , i put a small length of brass rod in the hole and silver braze it in. This seals the inside from oxygen. Like dsaul says, it is probably unnecessary but it is part of my routine.

Thanks a ton for sharing this, Andrew, that tip about saving vent holes for last is so crucial!

The value of losing up vent holes is a curiosity to me. Does it really matter? When I was learning at Ellis Briggs 50 years ago, they did repair and refinishing too. They hearth brazed the main triangles. The natural gas flame was huge like a dozen rosebuds all at once. They didn't drill a vent hole in the seat or head tube. When looking inside a top tube that came in for repair, it was pristine inside. No rust or anything. It had been sealed off from oxygen. So obviously a sealed tube works great to prevent rust.

What I assume is killer rust can come from condensation. Here in Michigan we can take our bikes out for a ride in the colder months and there will be a great drop in temperature between the house and the street. That will create water droplets inside the tubes. I've seen frames killed with condensation caused rust. That is why we put some kind of waxy brew inside the tubes. I would argue sealing is permanent and spraying inside is semi-permanent. Although not likely to be an issue until after we die .