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Tube Replacement?

Old 03-05-23, 08:01 AM
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Tandem Tom
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Tube Replacement?

I am wanting to dip my toe into the area of replacing a TT on a lugged frame. So am try to gain an understanding of how to prep the ID of the lug for brazing in the new tube.
So would really appreciate any advice.
Thanks!
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Old 03-09-23, 09:58 AM
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beng1
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Originally Posted by Tandem Tom View Post
I am wanting to dip my toe into the area of replacing a TT on a lugged frame. So am try to gain an understanding of how to prep the ID of the lug for brazing in the new tube.
So would really appreciate any advice.
Thanks!
With any soldering the secret is simply to have everything clean and fluxed. As long as you are using the same solder on the new tube as was used to hold the original in place, I would not worry about getting every trace of the old solder out of the lugs as long as the new tube will slide into the lug easily but with no play. I am surprised nobody here with experience on this has not chimed in yet.
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Old 03-09-23, 11:48 AM
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People don't always respond to his posts because he posts here, the email list, and facebook any time he asks a question. If the question gets answered elsewhere, people don't necessarily feel like answering it again.

I don't think there is any worry mixing fillers. I would happily use silver on top of LFB. The opposite might be trickier.
The problem is going to be getting a good fit.
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Old 03-09-23, 11:58 AM
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I sometimes do post in different areas because I think there are different audiences. So seem to frequent certain forums more often.
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Old 03-09-23, 03:15 PM
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It's fine, but you might not get answers here if everyone saw you got answers somewhere else.
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Old 03-09-23, 04:52 PM
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The main question different practitioners disagree on is whether to pierce the head tube and/or seat tube. Oh and whether to do it hot or cold. Those two questions are somewhat interrelated though, since there's no way to do this cold without piercing the HT and ST that I know of. And if you melt the tube out, you're probably not going to pierce the HT/ST. (Though you could)

In my experience, grinding the old tube out cold with a rotary file (burr) on a die-grinder is too slow, for someone doing this for money. We always melted the old tube out, just because that's very quick. Quicker if you have two torches (preferably both with rosebud tips), even better with a helper. One guy applying the heat, the other (with a thick foundry-style glove on) pulling gently on the vise-grip or whatever is clamped onto the tube stub being removed. Tugging a bit as it gets up to temperature means you can pull it loose a tiny bit earlier, before everything is fully molten, just at the point where the braze is really weak. Heating it until it's so molten that it falls out from gravity means hotter max temp, and a longer heat cycle. Just make sure any thin lug points are fully melted before you tug, lest the tube stub come out with pieces of the lug still attached. Lugs with decorative cutouts or extensive frills are always going to be in danger of losing pieces, so reconstructing the frills is sometimes part of the repair. Those are difficult either way though, just as tricky if you're grinding the stub out cold with a die-grinder.

It's a little perverse that the frames that are the most valuable (fancy, artisanal, thinned lugs) are the ones most likely to be worth repairing, but also the hardest to repair without ruining some delicate feature.

A lot of the original filler will come out with the tube stub, so there's not much cleanup needed in the socket. Inevitably a meniscus of filler will remain down in the crevices where the "wings" of the miter go, and that crevice is impossible to clean right down to the bottom, so the new tube will have to have its wings truncated, however much is necessary to allow the top and bottom of the miter to hit the HT/ST. Since it can be difficult to tell exactly how much to truncate the sides of the miter, I recommend just cutting them back a bit further than the minimum, to where you're sure that is no longer what's keeping the tube from going all the way in.

I have also removed the tube cold, but not by hand-grinding, I milled the stub out with a precision holesaw on the mill. We had a small enough milling machine that the head/spindle/pulley assembly all fit within the space where the TT goes, just had to remove the OSHA cover over the belt drive pulleys. Depending on setup time, that could be even faster than melting it out. Did that on the ST end only, melting out the HT end, one time on a frame where the seatstays were silver-brazed on. They would have come loose if I tried to melt the TT out. So the ST has the "giant vent hole", where you can tell the frame has been repaired by taking the seatpost out and looking inside. Hey, it's light weight! (drillium?) That frame went many years with no problems afterward, the giant vent hole didn't cause any strength or stiffness issues, the seatpost still tightens normally, no prob. Light rider though, with little seatpost stickout; maybe it'd be a different story for a way-sloping TT with lots of stickout leverage on the seat lug dunno. I'd worry just a bit more about the giant vent hole at the HT end, especially on this one bike which had barely-there bikini lugs (Otsuya aka Samson), very little of the HT is surrounded by lug. Most lugs reinforce more of the HT, to where piercing through the HT wouldn't worry me as much.

One more thing to add, I think frame repair is sometimes seen as a way to gain experience in framebuilding, for beginners. I disagree, since it can be more difficult to ensure a repaired frame is safe to ride, than if you started with all new clean parts and just built a frame. I wouldn't attempt a TT replacement until you've been a FB for a while. What's a while? I dunno maybe a year as a full-timer? Maybe that's too restrictive, so let's say more like 20 frames built, just to throw out a number. Some people are just naturals and learn faster of course. On the other hand I've had co-workers who never got really good at frame building even after years. Finessing out those stubs hot requires such perfect heat control, it's not for beginners. Grinding them out also requires great skill to do well, but at least it's slow, so you can stop and take stock of how you're doing, hopefully catch yourself before doing too much damage.

Mark B
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Old 03-09-23, 07:41 PM
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I don't like frame repair because it's usually something the original builder screwed up. If they didn't screw that particular thing up, they might have screwed something else up that I didn't notice. They probably screwed something up that compromises the repair. I hate the feeling of putting a bike back on the road when I'm not fully confident in it. Additionally, you fix it, you own all the screwups.

Anyway, I agree with Mr. Bulgier, repair is more difficult than building new in most cases. I never understood why people charge so little for repair. If you cite someone that's charging a lot, I'll just say they aren't charging enough. Maybe if they need the money to eat. In any event, I won't judge, but they aren't charging enough.
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Old 03-10-23, 06:43 AM
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Thanks for all your replies! They are greatly appreciated.
In the words of Dirty Harry "A man's got to know his limitations " I will be going g back to building from scratch and maybe picking up a few wrecked frames to practice tube removal!
Cheers!
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Old 03-10-23, 10:13 AM
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Originally Posted by bulgie View Post
In my experience, grinding the old tube out cold with a rotary file (burr) on a die-grinder is too slow, for someone doing this for money. We always melted the old tube out, just because that's very quick. Quicker if you have two torches (preferably both with rosebud tips), even better with a helper. One guy applying the heat, the other (with a thick foundry-style glove on) pulling gently on the vise-grip or whatever is clamped onto the tube stub being removed. Tugging a bit as it gets up to temperature means you can pull it loose a tiny bit earlier, before everything is fully molten, just at the point where the braze is really weak. Heating it until it's so molten that it falls out from gravity means hotter max temp, and a longer heat cycle. Just make sure any thin lug points are fully melted before you tug, lest the tube stub come out with pieces of the lug still attached. Lugs with decorative cutouts or extensive frills are always going to be in danger of losing pieces, so reconstructing the frills is sometimes part of the repair. Those are difficult either way though, just as tricky if you're grinding the stub out cold with a die-grinder.
That's pretty much how we did tube replacements at Trek. Two people, two torches, to evenly heat the entire joint. Tim Isaac showed us one of his tricks: cut out the middle section of the tube, drill a hole across the tube stub to accept the hooks of a bungie cord. Stretch the bungie cord around one of the intact frame tubes to apply even tension on the joint when the filler gets liquid. This pulls the tube straight out of the joint, no dangerous wiggling needed.
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Old 03-10-23, 07:00 PM
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John, did the tube ever take off like a rocket?
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Old 03-10-23, 08:40 PM
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Originally Posted by Tandem Tom View Post
John, did the tube ever take off like a rocket?
No, you don't want a lot of tension on the bungie cord, just enough to get it moving when the filler liquifies.
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Old 03-11-23, 10:15 AM
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I agree that getting the lug evenly heated so that the old solder melts evenly enough so the tube can be pulled out with a minimum of heat would be important.

How about cutting the top tube out leaving about an inch sticking out of the seat and head lugs, then heating the tube from the inside while holding it with a suitable pair of pliers and twisting and wiggling it ? The tube could be heated more evenly if the torch was heating from the inside of the tube than from the outside. Another thing to try on a junk frame first.
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Old 03-12-23, 06:40 AM
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twisting and wiggling is a good way to rip the lug.
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Old 03-12-23, 02:11 PM
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I became familiar with tube and other kinds of frame repair when I was learning to build frames in Yorkshire in 1975. I'll mention a couple things. Many classic European made frames were pinned to hold parts together before they were brazed. It is necessary to find where these pins are located and drill them out 1st before proceeding. Most of these frames were made quickly without getting the clearances perfect. In other words, parts were just jammed together (hammers were useful) before brazing. That means they might not come apart so easily because the tube is mechanically tight in the joint.

It is difficult for one person with a single rosebud flame in one hand and vise grips in the other to try and twist and pull out a tube of a brass brazed frame. When the lug is red hot it is easy for it to break apart or just distort when it is trying to be freed. That is why the pros on this board have already mentioned using 2 flames and some kind of straight pull system. Otherwise with only one flame, part of the joint might be too cool and another part overheated trying to bring the entire joint up to brazing temperature so the tube will release. My method is to cut out a small center section of the tube and drill holes on the end so some kind of weight can be attached. Then when the joint is brought up to temperature, the weight will pull the tube straight out. Typically I also need to give it a bit of a tap with my brass hammer to get it to start to move. That is to overcome the mechanical friction holding it in place.

One advantage I have is a powerful pressure pot sandblaster that can blast into the creases of the lug to blast out the remaining residue that stayed behind. The brass (or silver) wears away more quickly than steel. A common tube replacement is both a top and down tube when a frame has suffered a front end crash. In these cases I often replaced the head lugs as well instead of trying to take apart and clean up the lugs. Unless a frame had sentimental value, I usually thought the effort to replace tubes was too much bother.
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