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  1. #1
    Andrew R Stewart Andrew R Stewart's Avatar
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    New Build and Lug bending

    Earlier today I thought i'd have a question for the more experienced builders concerning how to change a lug's angles beyond what simple bending could do. But as I went along I was able to bend things far enough and keep the shore lines tight. Or at least that's what it looks like before the actual brazing.

    Details are, the top head lug from 74* to 77.5* and the St lug from 74* to 80.5*. I did the initial bending using the bending bars from Omar Khiel, tap hammer, crescent wrench and needle nose pliars. Next is doing some simple lug shape mods. After I miter up the tubes I'll fit the lug's ID and revisit their fit. As the fit gets looser with ID working the latitude for angle matching up will grow.

    As i worked at this today i had two conflicting thoughts. First was wanting to make my own lugs from tubes for the first time. Second was the "just fillet it" that will likely be what i do for the next projects.

    The other two big challenges with this frame is that I am trying to match an asthetic of a pervious frame and fit a wife I have not built for yet... Andy.

  2. #2
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    There isn't any real limit to how much the material can be bent or formed. However if the lugs are cast, that could be an issue. The sheet metal lugs that are generally unavailable or derided, are pretty much unlimited as to how much they can be bent. With cast, I would be curious to know whether they could be more safely bent if heated.

    Since basically the only issue with lugs is the look, I think you have a point about using other means to get there. I was reading this website about some famous Italian maker, and he did tandems, and just tigged the lugs. Lugs were originally welded. There really isn't any bad way to overbuild.

  3. #3
    Andrew R Stewart Andrew R Stewart's Avatar
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    The lugs are cast HJ. I've done this angle bending a number of times before. Depending on the direction of the bending I have gotten up to 6* before. This is a lot more then i would suggest to try without some experience. I'll be using brass as the internal voids get pretty large by this point.

    I hope to talk about this angle changing process with some real pros sometime in the future, maybe at the Phily show. Andy.

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    Pros seem to stick to fairly standard geometries, ; or they braze lugs, or they clad them. You can move metal all over but castings aren't meant for that. Golf clubs are cast for the most part today, but they can only be bent about 2% for fitting purposes, while the forged clubs have no practical limits to the bend. With sheet metal one could shrink that pocket.

  5. #5
    Randomhead
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    mostly it's the lower head tube lug that needs to be bent. The stuff seems to be pretty ductile, I have bent the heck out of some bb shells without issue

  6. #6
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    I'd be confident using it too. If it didn't break while bending it, I doubt it will break after all the heat is put to it. I'm talking about the cosmetics mostly, getting the chin tuck on the area that is gaping and needing the extra filler. You can bash sheet metal into almost any shape, the stock for those kinds of lugs started out flat. I was trying to find some info on forming investment castings. I wonder if the tucking could be done during the heating of the lug during installation. That kind of thing isn't too unusual, but I have no idea what ICs can take.

  7. #7
    Andrew R Stewart Andrew R Stewart's Avatar
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    Yes some lug forming can be done during the brazing. But mostly just shore line or points being tapped down tight against the tube. The mass and geometry of the lug at the crotches make reforming these areas MUCH harder. This is why when i bend a lug more then a small amount (maybe a degree or so) i use brass. This both makes filling the internal voids more likely as well as increasing the strength of the joint. Brass is far less dependent on the gap being "perfect" to maintain full strength (compared to silver).

    I supose one could lay an internal bead of brass in the sockets and then re size the ID of the lug to retain the right gaps for silver, after bending. Seems like as much work as utting the lug along the crotch and letting this slot compress or expand to help move the lug's angle and then brazing up this slot. And both of these seem like more work then just bending as needed and brazing the joint with brass. Andy.

  8. #8
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    I always say I don't do lugs because it is basically true, but the longer version is I almost got swept up into making only custom lug bikes as a side business at one point. I put a fair amount of time working out a way of tigging the lugs and it certainly is a long way around. I had to ream the stock turn it on a lathe, etc... So if you can bend them and get the look you want to boot, all the better.

  9. #9
    Andrew R Stewart Andrew R Stewart's Avatar
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    It's late and I'm still hyped up from an evening of shop work on the next frame. If i had a blog I'd write there but since I'm a ludite this forum is the most i can handle...

    This thread's subject is lug bending. But tonight's work was mitering the remaining of the main triangle. The overlap is I have adjusted the lugs and shell to the angles that the design states and now that the tubes actually are fitted together the adjusted sockets are found to be not spot on. This is not the first time I've dealt with this. Since I'm no pro or frequent builder there is an amount of relearning/discovery with each frame. So tonight as I work the tubes I get to find out how the initial lug bending went.

    Well I got 3 out of the 4 joints pretty close. The seat, top and lower head lugs are real close. As I shape their shore lines to the style this frame has (a match to another frame made last year) I will need to do some minor tweaking. Not bad considering that I shifted the angles a bunch on the seat and top head lug (6 and 4 degrees respectively) (the lower head lug needed less then a degree of change). This is well within my expectations.

    But the ST and DT angle in the shell need more work. The sockets needed to be closed up by about 4 degrees and I did so using the bending bars i got from Omar Khiel. But the differences between the bars and the tubes, that the DT has a S&S coupler in it, my building secquence with the ST brazed in seperately and my initially not changing the angle past what was wanted combine to make the DT fit up about a degree off (too large an angle). I think much of the bending angle and actual ST/DT angle is due to the ST not being held in the shell during brazing at the same angle, WRT the shell's socket, as was the case with the bending bars. In hind sight if I had bent the shell's sockets a degree or two past the intended ST/DT angle I might be spot on now.

    I intend to correct this with a few methods. With the ST brazed in the shell I can't just bend the shell more without the chance of the ST giving (and showing it's bluge from the distorting just above the shell's socket. Been there, done that). So I have done some black smithing to the bottom end of the DT as a first step. WHAT!? Tampering with a tube? Isn't that like a golden no no? Well yes and no. Tubes are bent all the time. Some times we call it raking, sometimes we call it tire clearance. In this case I have slightly bent the lower edge of the DT/shell miter inward. All of this within the overlap of the shell's socket. The second part of the angle shifting will come (not yet done, need turkey dinner first ) from grinding the shell's socket a bit. Mostly on the shell DT's underside. Then some more blacksmithing on the Dt socket shore line to keep the gap manageable. I might have to revisit the DT's miter lower edge shaping, we'll see. In the end the goal is the right ST/DT angle with no pressure to hold the tubes in place as this would close up the gaps and make flowing filler between the tight spot hard.

    I always think before these point in the building that i've got it all right. Then I fit togethet the lugs and tubes and have to go round again, manipulating a bit here and there. This makes me, once again, want to build with fillets and not lugs. And my next frames will be so. I just have to figure out how I'll deal with the forks in keeping with the rest of the frame's smooth joints. As usual as i get into the build of a frame i find mself thinking about the next one.

    Well i'm a couple of beers later and have slowed down enough to clean up and go to bed. Thanks for reading this and I hope some one finds a nuget of information here. happy turkey to all. Andy.

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