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Bottom bracket cluster mitering question

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Bottom bracket cluster mitering question

Old 04-03-21, 10:07 AM
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Gyro_T
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Bottom bracket cluster mitering question

I have been using the TubeNotcher Pattern Creation Tool on dogfeatherdesign.com for my miter practice. This is my first fillet brazed frame. I hoped that the tool would provide some guidance on notching a multi-axis airframe cluster, but apparently not. I just wanted to check with the forum to see if there were pointers regarding this. The downtube and BB are both 38mm and the seat tube is 28.6mm. Proceeding cautiously
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Old 04-03-21, 10:23 AM
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Are you asking about the two tubes having some overlap at the BB shell? Many just do this by hand and eye. Generally you decide which tube will have it's mitered end completely contact the shell (and for many builders this tube gets tacked or completely brazed/welded to the shell at this point) and then the other tube gets a small scallop/miter to both properly contact the shell and also nestle against the first tube. This gets easier after doing a few Andy
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Old 04-03-21, 10:25 AM
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I generate two mitre templates, one for DT to BB and one for DT to ST. Then my CAD software tells me the offset between them on the DT inside centreline in this case 11.29mm. So then I can trace them both onto the tube at once. I cut the DT to BB completely first and then sneak up on the DT to ST one checking the fit carefully as I go. It is the trickiest mitre on the frame and when welding it you have to be careful not to burn back the corners.

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Old 04-03-21, 10:38 AM
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Is the tube notcher software still there on the Nova site? I thought it did the dt/st notch correctly

Okay, it was the same software and it looks like it's not there any more. The bike specific version was hosted there, so I think I would reach out to the author of the software and see if he can help you
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Old 04-03-21, 08:33 PM
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The tube miter engine in RattleCad does this for you. I've been happy with it so far.
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Old 04-04-21, 01:13 AM
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Using a 38mm downtube on a standard BB shell will be tricky. For anything that isn't lugged, I use a T47 shell. The larger shell decreases overlap between tubes and if you offset toward the bottom of the shell, you can avoid it completely. Also, what headtube are you using? a standard 1-1/8" is 36-37mm which is smaller than your DT so the ears are going to require some work and delicate brazing - or you'll want to ovalize it.
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Old 04-04-21, 11:30 PM
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Thanks for the very specific nature of your reply. That is helpful.
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Old 04-04-21, 11:37 PM
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It is a 48mm head tube. I was concerned about the large DT and the bottom bracket. My Rove has an ovalized DT to solve that problem. I don't have an idea how I would ovalize it. I might try to find a piece of scrap to see if I can do a neat job while keeping it round.

Thanks to all for your generous sharing of knowledge,

G. Gearloose
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Old 04-05-21, 07:30 AM
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Every frame builder should have an ovalizing tool already. The bench vise. Andy
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Old 04-06-21, 08:39 PM
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Originally Posted by Gyro_T View Post
It is a 48mm head tube. I was concerned about the large DT and the bottom bracket. My Rove has an ovalized DT to solve that problem. I don't have an idea how I would ovalize it. I might try to find a piece of scrap to see if I can do a neat job while keeping it round.

Thanks to all for your generous sharing of knowledge,

G. Gearloose
Yes, ovalize at the BB works. you shouldn't have an issue at the HT. I agree with Andrew, the ovalizing tool doesn't have to be high-zoot.
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