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BB shell brazed now what?

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BB shell brazed now what?

Old 06-11-19, 06:46 PM
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TiHabanero
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BB shell brazed now what?

In the past I have brazed frames starting with the HT/DT joint first. This time around I started with the DT/BB shell and ST/BB shell joints first. Having not thought this through so completely, I am gathering input as to the next joint to be brazed.

I believe it will be the HT/lower head lug joint, then braze that to the DT.
Last joints to be brazed are HT/top head lug joint, then the TT and subsequent seat lug and head lug joints.

Am I close? Just trying to keep alignment correct and this is the only way I can see doing it.
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Old 06-11-19, 07:23 PM
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you are going to want to get the top tube in there before the dt/ht braze, because otherwise you will have to spring it in there.
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Old 06-12-19, 09:41 AM
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In my BJ (before jig) building I tried a few "hockey stick" arrangements and decided that what I liked best. I ended up doing the ST to shell 1st then add the TT, this is the 1st half of the main frame. 2nd half was the DT to HT. I found this made the DT length/BB miter easier to control. Back then I hand mitered each joint as I went along (although as I got better I would miter both ends of the TT and DT but a couple of mms long for the in situ final fit up). I mostly pin then tack then correct and complete the braze and correct again. I would fit the two halves and often find that I had to juggle the remaining miters a tad for the best fit up. Using only lugs back then I would use the through hole socket of the DT/BB as a fudge for the last bit of dimensional alignment, thus sometimes I was pleased that I had mitered the DT a tad long.

To this day, and even with a nice jig, I still attach the ST to the shell first.

It was the "prefab" issues of slightly bowed tubes, miter phasing/indexing (this before metal split tube clamps) and the resulting not perfect mating of the two halves of the main frame that made me start to set up the entire main frame before any tacking or complete brazing. This is now all I do, set up each joint in the jig one at a time then as the full triangle then tack, correct and complete braze. If I had no jig I would use a flat surface and some sort of riser blocks to position the tubing. But I would still set up the complete triangle as a unit (excepting the ST/BB which would already be done). Andy
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Old 06-12-19, 02:13 PM
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Using lugs. The tack method I use is to braze a small amount of filler to the two point tips on the two point lug, then adjust and fill in the rest of the lug afterwards. Is there a better way of tacking when using lugs?
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Old 06-12-19, 08:46 PM
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Tacking the tips of the lugs is what I and many do. I have seen and read of some who tack along the lug sides but I feel the off center line application of heat might promote distortions/twists. I do try to have all lug fit adjustments done prior to tacking though. Andy
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Old 06-14-19, 03:34 AM
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I'm a proponent of doing everything but the seat stays together. It's really easy to get movement between parts if the joints are done one at a time. If you have round sockets for the CS, then you might be giving up some freedom by doing the ST independent of the CS. Oval CS seem to have a lot more freedom

But the traditional way of doing a piece-by-piece build is to braze ST to BB, then HT to DT, then put everything together. I have done this a couple of times and it worked fine. I think if the DT and ST were already in the BB, I would just finish tacking all the front triangle joints now
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Old 06-14-19, 06:37 PM
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Unterhausen, this is what I have come to see as the best path forward. Already planning the next frame and will certainly do it differently!
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