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Discussion Starter · #1 ·
I ran into an issue on #2 that I didn't run into with #1. I'm wondering if you guys may be able to shed some light on it.

I've got a 56% silver brazed 1.25"x0.058 sleeve on my seat tube and I was TIGing the seat stays on and thought I blew a hole in it. I'd gotten about half way around the stay and as I was standing on the pedal (I've gotten away from the pulser and am manually pulsing with the pedal) and just about to back out of it and move on, the puddle basically exploded outward, covering my electrode in molten filler rod and left a crater in the weld. I thought perhaps my gas blew off so I cranked up the gas a bit, hit it good with the steel wire wheel to clean it up, resharpened my tungsten, tried to fill it in and the same thing happened in this one stop. I cleaned it again, moved on and finished the weld out and then came back to that spot and filled it the best I could but it doesn't look great.

I'm thinking what happened is that the puddle got hot enough that the silver mixed with the steel in the ST sleeve and it contaminated the weld. I can't imagine that I burnt through 0.058" and into the silver without burning a hole in the seat stay, but that's all I can think that happened here.

Any ideas?
 

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that's probably what happened. You should always do the silver work after all the welding to avoid this. Fill the blemish with silver for this one.
 

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Do the silver last.

Yep, you managed to get the silver/flux to contaminate things. All's not lost, the joint is probably ok anyway, but in the future, do the silver in the top and bottom of the sleeve *after* you TIG everything. The silver is really just to fill the gaps between the sleeve and the seat tube - you don't need it for structural reasons in general. So you don't need to worry about getting silver all the way through like you would with a lug.

-Walt
 

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I have had this happen once. It was on an externally butted seat tube with a sleeve as well. I figgured that the taper had allowed a pocket of flux to stay in the cavity and thats what blew up on me. I can understand the advice and argument for silvering later but I like to have the sleeve, bb and bosses all done before welding the bike up and have not had the problem since. It could be better tig heat control or more thourough silvering, what ever it is I'll take it.
I'm sorry that it happened to your bike, it was quite a surprise when it happenend to me! (i'm sorta glad I'm not the only one though ;-)
 

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Discussion Starter · #5 ·
j-ro, no worries, I'm sort of glad it happened to you too for the same reasons. It certainly did surprise me.

So Walt, the thing I don't get about doing the silver last is how? In other words, I need to have the front triangle done and could skip brazing the lug on until after I have everything done, but then with the SS on it, the TT on it, essentially a done frame, how do I clean and flux the joint before silver? Are you suggesting that I just stick some flux on the tube, let it run down in a potentially dirty joint, and draw the silver in there too? I suppose that would be ok 'cause it just needs to have a little on the top and bottom. I'm just curious if that's what I'm "supposed" to be doing.

The other thought is silver brazing the SS to the lug instead of TIG welding them. I'd think even in an MTB application, silver should be fine with the amount of area I'd have around the tube--many times more than a traditionally built lugged frame.

Anyway, all is not lost--it cleaned up ok. Pictures to come tomorrow.
 

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Yup.

In my experience (hundreds of these, now), by the time you weld on the toptube and seatstays, the seat sleeve is not going anywhere - simple distortion will hold it in place pretty darn well, if nothing else. So the silver (I actually just use brass) in the top/bottom is not so much structural as aesthetic. Clean the joint up nicely before you weld it, and when you're all done, throw a little flux in the top/bottom and flow a bit of silver or brass in. Your goal is not full penetration of the joint, it's just to seal things up and make it look nice.

Using silver or brass for the seatstays is certainly another way to go about it. You'd still melt at least some of the silver in the sleeve, but there's no risk of blowing through. Filing a fillet seatstay cluster is a PITA, though, I'll warn you now...

-Walt

jay_ntwr said:
j-ro, no worries, I'm sort of glad it happened to you too for the same reasons. It certainly did surprise me.

So Walt, the thing I don't get about doing the silver last is how? In other words, I need to have the front triangle done and could skip brazing the lug on until after I have everything done, but then with the SS on it, the TT on it, essentially a done frame, how do I clean and flux the joint before silver? Are you suggesting that I just stick some flux on the tube, let it run down in a potentially dirty joint, and draw the silver in there too? I suppose that would be ok 'cause it just needs to have a little on the top and bottom. I'm just curious if that's what I'm "supposed" to be doing.

The other thought is silver brazing the SS to the lug instead of TIG welding them. I'd think even in an MTB application, silver should be fine with the amount of area I'd have around the tube--many times more than a traditionally built lugged frame.

Anyway, all is not lost--it cleaned up ok. Pictures to come tomorrow.
 

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Walt said:
Using silver or brass for the seatstays is certainly another way to go about it. You'd still melt at least some of the silver in the sleeve, but there's no risk of blowing through. Filing a fillet seatstay cluster is a PITA, though, I'll warn you now...
-Walt
Not if you braze it well to begin with.....:D

I remember when I did TIG things a bit.. I got so frustrated with doing tight seat-stay junctions and I was so much better at brazing them I just gave up on it. I would TIG the entire frame and fillet braze the stays and everyone seemed to like it a lot and could play a few tricks with the stays to make them look a touch different.

Personally, I always try to get full flow of the seat collar. I agree that its probably pretty meaningless but I feel better about it. I often will drill some holes or make a decorative treatment and the point isn't really making it look good as giving me a feed point midway up the sleeve for full penetration.
 

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Heh!

Yeah, that's why I TIG - good lord, I can't fillet braze to save my life - I'd spend the rest of my life filing and/or calling Steve at 3am, sobbing uncontrollably....

If you're not TIG welding the seat cluster, the question is of course academic. IMO, having full silver/brass penetration of a ST *sleeve* (note, I didn't say "lug") is of secondary concern to making sure your TIG joinery of the toptube and seatstays is nice and uncontaminated. For me, this means doing the sleeve brazing after the TIG work.

YMMV. I have never seen a sleeve come loose in any situation, regardless of the methods used to join it or the rest of the cluster, so how you do it is pretty much your call.

-Walt

dbohemian said:
Not if you braze it well to begin with.....:D

I remember when I did TIG things a bit.. I got so frustrated with doing tight seat-stay junctions and I was so much better at brazing them I just gave up on it. I would TIG the entire frame and fillet braze the stays and everyone seemed to like it a lot and could play a few tricks with the stays to make them look a touch different.

Personally, I always try to get full flow of the seat collar. I agree that its probably pretty meaningless but I feel better about it. I often will drill some holes or make a decorative treatment and the point isn't really making it look good as giving me a feed point midway up the sleeve for full penetration.
 

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Discussion Starter · #10 ·
Dave, you do bring up good points on what a PITA welding out the SS at the top is. That's one reason why I'm considering silver brazing those too. It would be faster for me--I'm getting ok w/ the brazing. Ice-T had a song way back in the day where there's a lyric where he says "you got to get in and get out, if you're expecting to last" when talking about "the game". I've adapted that to brazing. Get in and get out:




Walt, thanks for the advice on the welding side too. I will certainly try that next time too if i decide to weld these from here on out. I really don't know what I want to do yet. I do like the idea of not having un-silvered flux in the joint and having full flow but I also see that it isn't necessary either--but still, it bothers me to know it isn't full. I'm certainly leaning to brazed tops moving forward now.
 

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dbohemian said:
Not if you braze it well to begin with.....:D

I remember when I did TIG things a bit.. I got so frustrated with doing tight seat-stay junctions and I was so much better at brazing them I just gave up on it. I would TIG the entire frame and fillet braze the stays and everyone seemed to like it a lot and could play a few tricks with the stays to make them look a touch different.

Personally, I always try to get full flow of the seat collar. I agree that its probably pretty meaningless but I feel better about it. I often will drill some holes or make a decorative treatment and the point isn't really making it look good as giving me a feed point midway up the sleeve for full penetration.
This is sort of what I've come up with, I drill what is to be the vent hole for the TT into the collar, 7/16" or so but not into the seat tube. this gives me a great spot to feed silver that finds its way to the back of the tube where the SS's join in. Then I drill the hole into the seat tube. I only had the blowout problem once but it was enough.
 

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Discussion Starter · #12 ·
j-ro said:
This is sort of what I've come up with, I drill what is to be the vent hole for the TT into the collar, 7/16" or so but not into the seat tube. this gives me a great spot to feed silver that finds its way to the back of the tube where the SS's join in. Then I drill the hole into the seat tube. I only had the blowout problem once but it was enough.
That's an elegant way to do it.

Do you think the blowout problem was associated with silver getting into the weld or flux getting into the weld?

The reason I ask is the first time I did this, no problems--and my heat control was WAY worse than this time. However, this time, my sleeve was a bit tighter than last time and I'm concerned that I didn't flow the silver as well as the first time. In other words, there very well may be a cavity in the that doesn't have silver in it and is still fluxed--though I'd suppose that most of the flux that would be have been in there would have been pushed away during the sliding the sleeve on too.

I may cut a hunk of tubing and experiment with it just to see if I can reproduce it on a test coupon instead of reproducing it on a frame in the future.
 

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jay_ntwr said:
That's an elegant way to do it.

Do you think the blowout problem was associated with silver getting into the weld or flux getting into the weld?

The reason I ask is the first time I did this, no problems--and my heat control was WAY worse than this time. However, this time, my sleeve was a bit tighter than last time and I'm concerned that I didn't flow the silver as well as the first time. In other words, there very well may be a cavity in the that doesn't have silver in it and is still fluxed--though I'd suppose that most of the flux that would be have been in there would have been pushed away during the sliding the sleeve on too.

I may cut a hunk of tubing and experiment with it just to see if I can reproduce it on a test coupon instead of reproducing it on a frame in the future.
I think in my case it was flux, all I had was an external butted st and I really wanted to use a sleeve. This was a bad combo (and quite some time ago), it allowed a lot of flux in there as it was a large void.
I know it had a ton to do with heat control as well. When it blew, there was no cleaning it up and finishing the job, it was c o n t a m i n a t e d. Even though i haven't had the problem since, I have gotten the sleeve hot enough to lose the silver at the shorelines from time to time, this tells me that it was a paticularly bad silver job on the one that blew.
I believe walt when he says its ok to do it later and its good to know that its a proven. I'm just not having any more problems with my method so I'm sticking with it for now.
 

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You might also consider brazing the st sleeve with brass, it'll have a higher remelting point. Then use the pulser when you tig the stays, as the pulser is actually designed for reducing heat input on thin materials. Don't screw with 1 or 2 pps, either. Turn it up to 10+, with your background amperage and your on time both 35-40%. Give it plenty of pedal and move fast, don't stay in one place too long. Trust me on this, I've got plenty of experience welding on stainless and Inconel parts that were brazed together. If you can't or don't want to use brass, this will still work with silver, but it will be a little trickier.
 

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Discussion Starter · #15 ·
edoz said:
You might also consider brazing the st sleeve with brass, it'll have a higher remelting point. Then use the pulser when you tig the stays, as the pulser is actually designed for reducing heat input on thin materials. Don't screw with 1 or 2 pps, either. Turn it up to 10+, with your background amperage and your on time both 35-40%. Give it plenty of pedal and move fast, don't stay in one place too long. Trust me on this, I've got plenty of experience welding on stainless and Inconel parts that were brazed together. If you can't or don't want to use brass, this will still work with silver, but it will be a little trickier.
Hmmm, I didn't think about setting the pulser way high. I'll do some experimenting. I've got plenty of time to practice some of this before it's time to make a decision on the next one.

BTW, you get my PM on the other forum?
 

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Discussion Starter · #18 ·
edoz said:
You might also consider brazing the st sleeve with brass, it'll have a higher remelting point. Then use the pulser when you tig the stays, as the pulser is actually designed for reducing heat input on thin materials. Don't screw with 1 or 2 pps, either. Turn it up to 10+, with your background amperage and your on time both 35-40%. Give it plenty of pedal and move fast, don't stay in one place too long. Trust me on this, I've got plenty of experience welding on stainless and Inconel parts that were brazed together. If you can't or don't want to use brass, this will still work with silver, but it will be a little trickier.
Man, so you can weld like that? I jammed the PPS way up to 10, then 15, then 20 and I like how fast it tacks at about 15 and that the part is still cool to the touch for the most part. But I can barely see what's going on. I suppose I need to practice but that strobing is enough to make a person nuts! Very cool tip though and great meeting with you last week. BTW, I'll drop off that frame on Wednesday for sure.
 

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Discussion Starter · #20 ·
smdubovsky said:
Hmmm, that's interesting. I'm going to have to play with that some more. I'd bet that 100 PPS would be similar to no pulser but maybe help control the head more. I like this especially, but then it may just be marketing BS too:

Reducing the number of pulses per second widens the weld bead. Slower pulsing also helps agitate the puddle and release any porosity or gas trapped in the weld (this is very helpful when welding aluminum with AC pulsed TIG). Some beginning TIG welders use a slow pulsing rate (perhaps .25 to 1 PPS) to help them develop a rhythm for adding filler metal. When beginners weld aluminum, an AC pulsed TIG rate of about 4 to 8 PPS may enhance cosmetics too. However, an experienced TIG welder may set a much higher PPS rate. It is not uncommon for them to weld aluminum at 4 to 130 PPS and stainless steel at 100 to 500 PPS (rates higher than 500 PPS are generally automated).
 
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