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PostPosted: Thu Jun 14, 2018 7:38 am 
Retro Guru

Joined: Tue Jun 03, 2008 4:31 pm
Posts: 790
Firstly, this is not going to a frame builder. That costs more than its worth.
Got a Columbus Brain tubed frame that has a cracked down tube, just above the bottle boss. Currently used about 3 times a year as my hill climb bike with a extra long seat post firmly clamped at the top and a long bottle cage bolt through and into a tapped hole in the post. No noticeable issues .
Anyone managed any jiggery pokery with a welder ( of any kind) or gas welder to fix such a crack? Maybe drop a steel seat post down and open up the crack to weld both together? Got the technology and skill base within the family.
Bike has more sentimental value than real and I like playing with problems.


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PostPosted: Thu Jun 14, 2018 8:11 am 
King of the Skip Monkeys
King of the Skip Monkeys

Joined: Wed Nov 07, 2007 4:34 pm
Posts: 28820
pics!

I'll have a frame builder on standby who'll give you a decent opinion.


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PostPosted: Thu Jun 14, 2018 8:19 am 
King of the Skip Monkeys
King of the Skip Monkeys

Joined: Wed Nov 07, 2007 4:34 pm
Posts: 28820
Right!

Our frame builder says:

Its a very odd place for a crack!

The tubing at that point may only be around 0.5mm and will have to be REALLY clean before any attempt at welding. It would be easier to braze than to try and join two bits of very thin metal.

If the crack is from the bottle cage boss, remove it and braze in a reinforcing diamond bottle boss.

It can be sleeved and if you shape the sleeve nicely it can be made to look like a posh lug.

More complicated would be to internally sleeve it ...


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PostPosted: Thu Jun 14, 2018 8:24 am 
GOLD | PoTM | Rider | rBOTM
GOLD | PoTM | Rider | rBOTM
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Location: 54 Festive Road Winchcombe GLOUCS Yarp...
Has he had his toast?


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PostPosted: Thu Jun 14, 2018 8:41 am 
Retro Guru

Joined: Tue Jun 03, 2008 4:31 pm
Posts: 790
Crack is around frame (270 degrees) about 5cm above boss. I suspect that it was made too delicate for the use it had or maybe too much pressure in a work stand. Local 753 approved builder for his own use and pushing boundaries somewhat.
Suspect a splint within the tube may be needed. Bet this will be easier than the top and downtube on the trike I have.


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 Post subject: Re:
PostPosted: Thu Jun 14, 2018 8:58 am 
Gold Trader / MacRetro rider
Gold Trader / MacRetro rider

Joined: Thu May 06, 2010 10:05 pm
Posts: 7144
Location: Aberdeen
It's steel, so anything is possible :D
I recently had a broken chainstay mig welded, it's not pretty but it's holding together thus far.
I'd guess some internal sleeving would work if it didn't interfere with the seat post. Or an external sleeve.
If you have the skills within your family I'd ask them what/if they think they can do it, there a no guarantees with repairs like this though.


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PostPosted: Thu Jun 14, 2018 3:05 pm 
retrobike rider
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
Posts: 2162
Location: A wretched hive of scum and villainy...
The Columbus Brain tubeset wasn't built for off-road, but the differences are mainly in the stays. The builder would have had to use stays from another tube group anyway.
0.6mm wall of the Brain seat tube is the same gauge and material as Cyber, Genius and MAX, which are all listed for off-road use, so probably not pushing boundaries too much.

Seat tube centres are very low stress and unaffected by the heating around joints. Tension from bracing the double triangle and a little torsion along the headtube to rear axle axis at best. The tube is completely capable of taking normal riding stresses or workstand clamping.
Maybe a roof-rack crash, over-zealous seat tube reaming, or fretting from an undersized seatpost?

Capilliary braze an internal 27.3-27.4mm Ø sleeve is the neatest way to do it. Drill a few extra feed/sight holes to make sure that the bronze or silver flows all around, and make it long enough to be able to fill the extra hole you drilled for the seatpost screw.

1995 catalogue page for Brain:
Attachment:
Brain-2.jpg
Brain-2.jpg [ 61.99 KiB | Viewed 193 times ]


All the best,


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 Post subject: Re:
PostPosted: Fri Jun 15, 2018 11:08 am 
Retro Guru
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Joined: Mon Sep 24, 2012 9:10 pm
Posts: 945
Quote:
Firstly, this is not going to a frame builder. That costs more than its worth.


Yeah the economics of steel frame repair are up the creek. I think it stems from the days when we(?) couldn't afford a new one. These days I guess you can get two old frames on ebay or whatever for less than the cost of getting the one(?) you've already got put back in order, or probably five old frames for less than the cost of attending one of those frame-building courses.


Must get to grips with brazing (and un-brazing) one of these days. I think I've got most of it theoretically, but zero practical experience... a bad recipe..
..


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 Post subject: Re: Re:
PostPosted: Fri Jun 15, 2018 1:02 pm 
GOLD | PoTM | Rider | rBOTM
GOLD | PoTM | Rider | rBOTM
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Location: 54 Festive Road Winchcombe GLOUCS Yarp...
torqueless wrote:
Quote:
Firstly, this is not going to a frame builder. That costs more than its worth.


Yeah the economics of steel frame repair are up the creek. I think it stems from the days when we(?) couldn't afford a new one. These days I guess you can get two old frames on ebay or whatever for less than the cost of getting the one(?) you've already got put back in order, or probably five old frames for less than the cost of attending one of those frame-building courses.


Must get to grips with brazing (and un-brazing) one of these days. I think I've got most of it theoretically, but zero practical experience... a bad recipe..
..



Get a couple of old frames to play on?


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 Post subject: Re:
PostPosted: Fri Jun 15, 2018 4:31 pm 
Retro Guru
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Joined: Mon Sep 24, 2012 9:10 pm
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Oh I've got an old frame to play on... I just don't think I'm gonna get away with turning 'chez torqueless' into a blacksmith's forge... not yet awhile anyway..

I wouldn't go near thin alloyed steel bike tubing with welding temperature. As far as I understand it, (which ain't far) anyone who does is either super-skilled or ignorant of the ramifications.


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