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Attaching lugs to BB shells

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Attaching lugs to BB shells

Old 03-15-19, 07:54 AM
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bakerjw
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Attaching lugs to BB shells

After having our first tandem custom built, I seem to have developed a bit of a fascination with frame building. Of particular interest is building with bamboo. I know that there are kits out there but having my own stand or 2 of bamboo I have started to mull around what it would take to put together components to build from scratch using my own bamboo.
I have a concept in my head, plenty of experience with carbon and fiberglass fabrication, my own Induma mill and Hendy lathe, ESAB tig/mig/stick welder and plenty of mechanical background to go along. I just have a couple of more things to mull around before I pick up some starter materials.

In looking at framebuilder supply, I have found dropouts that will meet my needs but the shells with lugs might have larger lugs than I would wish to use. If you ever do it, how do you about attaching your own tubing to blank shells? Tig, mig or braze? I would expect braze to not be strong enough but that is why I am asking here.

Thanks
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Old 03-15-19, 09:16 AM
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Fillet brazing 2 tubes together with brass to make a lug works fine. It is way more than strong enough if you do it right. You can do it will Fillet Pro silver from Cycle Design too but it is a lot more expensive. Andy Stewart will chime in as he has pictures of making his own lugs. Tig wilding works as well but in my opinion isn't as attractive.
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Old 03-15-19, 03:33 PM
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As Doug says. It isn't hard to make your own lug or BB. 4130 tubing is easily available from a number of sources and in a considerable range of diameters and wall thicknesses. BB shells that are straight/threaded "tubes" are also widely available. Most of the self made lugs that I see are brass brazed together. If the shore lines are ornate they are created after brazing the blank up.

A couple of questions though- What material will the fittings (Bb shell) need to be? Steel? This effects what filler/joining you use. Are these fittings going to be external to the bamboo? Or do the tube "stubs" fit up inside the bamboo? Are you up to speed with the different types of bamboo (for frame making) and your growing climate? I have a thread on a recent lug and BB making project here: Lug Making Andy
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Old 03-15-19, 06:00 PM
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I wouldn't use metal lugs with bamboo. Which ones have you seen that you consider '"too large"? Perhaps you can explain how you envision joining things.

Mitered and wrapped lug construction is well proven as either a carbon or bamboo joining method.
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Old 03-16-19, 08:04 AM
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Thanks for all of the comments and links. I am still very early on in the thought process and working things out in my head so nothing is cast in stone.

I was planning on using smaller lugs to insert a few inches into the bamboo primarily around the BB shell but also at the dropouts. The sealing mixture would be a combination of fumed silica and cut glass. I would then wrap the outer surface in carbon thread for a couple of inches to keep the bamboo from splitting and aesthetics.
I've watched several of the videos and they are quite impressive with a lot of good ideas. One possibility being going with fiberglass/carbon fabric prior to wrapping.

As I said, I am still early on in the process and just gathering my thoughts and taking whatever guidance and benefit of experience that I can get.

If you want to see what 94 days of hell looks like, you can check this link. This was when I rebuilt the internal structure of my 18' Stratos center console boat.
Stratos / Rebuild | Beth and John Baker's Photo Gallery

I also used to work for a company where we did custom carbon and kevlar piece work.

Thanks again.
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Old 03-16-19, 08:11 AM
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The inside of bamboo is too soft to support that sort of joint.
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Old 03-16-19, 02:05 PM
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I would think an internal "lug" would need the bamboo tube drilled/reamed to the right ID to have the "lug" slide in and have the right gaps for the bonding agent to hold tight. (And I wonder about drilling small holes into the "lug" tube to increase the mechanical locking together with the bonding agent). Whether the bamboo's insides are workable and/or strong enough I have no idea. Andy
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Old 03-16-19, 05:43 PM
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Workable but not strong enough.. "Panda" used this sort of idea but the lug was doubled so that there was an internal and external lug. The bottom bracket alone probably weighed more than a typical frame.
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