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Bottom Bracket Assembly - which (oversized) sizes to use for my bike frame jig

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Bottom Bracket Assembly - which (oversized) sizes to use for my bike frame jig

Old 07-15-20, 07:32 AM
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apollodriver
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Bottom Bracket Assembly - which (oversized) sizes to use for my bike frame jig

i am currently working on a bike frame jig -

i am currently workin on the Bicycle-Frame-Building-Jig that is designed by tanner W at instructables

which bottom bracket assemblies should i work out:

To secure the cylinder that holds the 5/8 rod to the back plate I drilled and tapped the back of it. I drilled corresponding holes in the back plate and screwed them together. I also drilled and tapped the cylinder for small set screws. These will hold the rod securely perpendicular to the ST support. The cones are held in place on the rod with locking collars from McMaster.
The big mistake I discovered once I started building with this jig was that I made the BB cones out of aluminum. The tight fit of the steel BB shell on to the big cone causes issues once you start heating. The aluminum expands differently than steel and gets really stuck in the BB shell. I need to make new cones out of steel. Mount the BB assembly to the ST assembly at the correct position (distance from BB center to channels in the ST assembly, see drawings).
- well unfortunatly i cannot post a link - untill i have reached 10 postings.

The question is - which bottom bracket-assembly-types would you suggest!?
which axles and dummy shells should i drill

btw - see the whole descritption of the thanner frame jig - at instructables. com

love to hear from you
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Old 07-15-20, 07:40 AM
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unterhausen
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Welcome to the forum

https://www.instructables.com/id/Bic...-Building-Jig/

I think as long as you can get a standard English bb in both 68 and 73, you should be fine. It's hard to deal with the press fit sizes because AFAIK nobody is selling facing/reaming tools for them.
Paragon has a ton of bb shells available, so you could match what they sell. but I think the two most standard sizes will probably do for now. It looks like that fixture is adjustable for width, so you only need one set of blocks
https://www.paragonmachineworks.com/...lls/steel.html
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Old 07-15-20, 09:13 AM
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Originally Posted by unterhausen View Post
Ot's hard to deal with the press fit sizes because AFAIK nobody is selling facing/reaming tools for them.
They probably don't need reaming or facing. BB shells are thick enough that you don't get any weld-through or distortion and press fit BBs aren't relying on the outside faces for the bearing alignment.

​​​​​But I don't see much reason to use anything other than regular threaded BB shells on steel frames. I guess you might want to use one of those funky ones for an eccentric BB. I would rather use horizontal dropouts myself but some people like those eccentric BBs.
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Old 07-15-20, 09:26 AM
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unterhausen
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For my tandem eccentric, I just used the insert to mount it on the fixture.
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Old 07-15-20, 02:10 PM
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Originally Posted by guy153 View Post
They probably don't need reaming or facing. BB shells are thick enough that you don't get any weld-through or distortion and press fit BBs aren't relying on the outside faces for the bearing alignment..
I don't know about other suppliers, but Paragon press fit bottom brackets are all supplied .5mm undersized and need reaming regardless of weld distortion.
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Old 07-15-20, 02:23 PM
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This is the bottom bracket mount that I used on my jig and a few that I made for other people. The mounting bracket idea was copied from Kris at 44 Bikes and the cups are held with set screws on the 3/4 precision ground rod.



This photo shows the bracket attached to the 40mm extrusion.


This is an alternative mounting method that I made for someone, using the same cups and 3/4" precision ground rod.
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Old 07-15-20, 03:01 PM
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If I ever make a bike with a 100mm bb, I'm going to have to throw the post in the lathe again.
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Old 07-22-20, 05:07 PM
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Originally Posted by dsaul View Post
This is the bottom bracket mount that I used on my jig and a few that I made for other people. The mounting bracket idea was copied from Kris at 44 Bikes and the cups are held with set screws on the 3/4 precision ground rod.



This photo shows the bracket attached to the 40mm extrusion.


This is an alternative mounting method that I made for someone, using the same cups and 3/4" precision ground rod.
Those cups would make a really nice addition to a Bringheli jig. I may have to do this.
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