Brompton project

JhnBssll

Über Member
Location
Suffolk
As some may have seen in my wanted post I've managed to find a donor bike for my Brompton project, thanks again to @ABikeCam - I hope to get it back up and running and will document my efforts here :okay:

Here is the bicycle in question:

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It has been stripped for spares so there are a few items missing which will need to be sourced, but before then I have a rather lovely set of cracks in the seat tube to try and deal with...

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I've shown it to a few of my welder/fabricator friends and responses have ranged from "Ha, good luck with that!" to "That'll MIG up a treat buh..." so I'm not really sure what to expect, other than several hours of entertainment in the garage and plenty of peace and quiet for Mrs Bssll :laugh:

One thing that I have read a number of times is never to try and weld a brazed frame, which of course the Brompton main frame is. I've taken this as a challenge and have bought myself a new toy :laugh:

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First job will be to strip it down and put the parts to one side, then I'll clean the frame up and try and align the cracks before trying to (very cautiously) weld them up, bit by bit, with plenty of cooling. No idea how that will pan out but I've got my lbs looking in to replacement main frame's if/when the worst happens and the brazing melts :laugh:

I've sourced some brake bosses and am looking in to the possibility of replacing the caliper brakes with mini V-brakes. For no reason other than it would be a fun project. I've also got a cheap dynamo front wheel on the way, £75 new from eBay :laugh: It seems you can get fairly cheap coloured rims so I might look in to those when I've worked out a colourscheme later on - the frame will be getting a full rattlecan respray when I'm done with my tweaks :laugh:

Anyway thats all for now, I'll post pics when I have had a chance to make a start. I sincerely hope I don't set fire to anything, it's been an awful long time since I've wielded a welding torch :ohmy::laugh:
 

SkipdiverJohn

Veteran
Location
London
One thing that I have read a number of times is never to try and weld a brazed frame, which of course the Brompton main frame is. I've taken this as a challenge and have bought myself a new toy :laugh:

View attachment 490846
Two possible issues are weld contamination from the brass, and joint failure due to heat input.
The latter should not be a problem if you are using MIG, as it has less heat input than MMA (arc) and way way less than gas torch welding. Just do it in short bursts, like when tack welding.
Brass contamination may be an issue if the crack is at a point where it was brazed during farbrication, as it has a lower melting point than steel. You'll just have to hope it doesn't cause any problem.
Get your MIG set up first and play with it on some scrap. Those cheaper machines like the Clarkes have pretty rudimentary wire feeds and are not always very smooth. I've got a similar one and I've also got a semi-professional quality Portamig machine - and the difference in ease of use is like night and day.
 
OP
JhnBssll

JhnBssll

Über Member
Location
Suffolk
Two possible issues are weld contamination from the brass, and joint failure due to heat input.
The latter should not be a problem if you are using MIG, as it has less heat input than MMA (arc) and way way less than gas torch welding. Just do it in short bursts, like when tack welding.
Brass contamination may be an issue if the crack is at a point where it was brazed during farbrication, as it has a lower melting point than steel. You'll just have to hope it doesn't cause any problem.
Get your MIG set up first and play with it on some scrap. Those cheaper machines like the Clarkes have pretty rudimentary wire feeds and are not always very smooth. I've got a similar one and I've also got a semi-professional quality Portamig machine - and the difference in ease of use is like night and day.
Agreed on all counts :okay: I'm going to try and pop via my local scrap metal merchant on my way home from work tomorrow and see if I can buy some bits for some trial welds :becool:
 
OP
JhnBssll

JhnBssll

Über Member
Location
Suffolk
I've been thinking about what direction to take this bike in a bit recently. My projects have a tendency to escalate quickly and this seems to have happened again :rolleyes:

The dynamo front wheel arrived in the post last week :okay: It's brand new, never had a tyre mounted on it. Total bargain :becool:

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Also to arrive this week were the brake bosses - I bought a couple of different types as they were pretty cheap (a few quid each) and I only had a basic picture of them to go off :wacko:

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Holding them up to the frame and forks it seems I've chosen well, I think they'll work a treat. I just need to practice my welding now :laugh:

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I've also made a few other purchases :rolleyes: This is where it begins to escalate... Two nice new black rims, one 28 hole to rebuild the dynamo front hub in to and one 36 hole to build up with the bargain Alfine 11 Di2 hub I found on eBay :whistle: Of course this means I will need to modify the spacing of the frame but I'll wait for the hub to arrive before I decide how to go about that. Hopefully I can heat it and stretch it rather than having to cut and weld but we shall see... Of course this means I need to keep an eye out for other bargain Di2 bits now and the alfine stuff doesnt seem to come up very often. Fortunately it'll likely take a while to get the frame stripped, repaired, modified and repainted so no pressure :smile:

Next job is to source some reasonably cheap mini v-brakes so I can work out where to put the brake bosses :okay: And of course get some welding time in :laugh:
 
OP
JhnBssll

JhnBssll

Über Member
Location
Suffolk
I started the strip down this afternoon :smile: I've got as far as trying to remove the stem but it doesnt seem to want to budge so I've left it soaking in plusgas and will try again another day :laugh:

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I've hit a couple of minor snags; I don't have a tool that fits the bottom bracket, haven't seen one like this before so will investigate what's needed to whip it out and get something ordered :laugh:

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The lower hinge bolts were a bugger to release but I got there in the end! I presume I'll be able to get the bits from my lbs (a brompton dealer) to replace the hinge if needed, probably worth doing if I'm able to repair the cracks.

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Speaking of cracks, I've found a new one and suspect I may have created it while trying to loosen the stem :whistle:

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I think the forks are now scrap which is a shame but I'll strip the paint off and see if they're salvagable first. I've found replacement forks for sixty quid so it's far from the most expensive error I've ever made :laugh: If the forks are indeed beyond repair it gives me a chance to practice some welding too, I've got a few spare brake bosses so will probably weld a pair on for practice :okay:

Once I get the stem and forks removed I'll pull those headset cups out and in to the bin, there's no place for rusty chrome on this bicycle :tongue:
 

FrankCrank

Professional layabout
.....another thing with brake bosses, at least on all those I've measured, is they are spaced centre to centre at 80mm, give or take a little.
There may be a good reason for this, such as allowing the brake arms to operate correctly, but in any case I'd aim at that spacing.

Not wanting to dampen your enthusiasm, but you really are chucking yourself in at the deep end as regards welding. I TIG weld all my stuff, and O/A would be a second choice, but MIGing would be hard to achieve, especially on brake bosses. Getting two pieces of metal to stick together is not the same as welding :wacko:

I hope you have the courage to show us some of your welds prior to attempting this, and best of luck.......
 
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JhnBssll

JhnBssll

Über Member
Location
Suffolk
I just brandished a welding torch for the first time in about 15 years. 20 minutes of playing about with the old brompton seatpost and tweaking the settings and my technique. I started from the left in case it's not entirely obvious :blush::laugh::laugh:

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Clearly theres more practice needed but I'm at least confident now that with some practice I can be reasonable at it, and that's all I'm really aiming for :laugh:

A few more bits have arrived but I'll post another update when more has happened. It's been a lousy week so hopefully I'll get more chance to play in the garage and forget about life for a while soon :laugh:
 

EltonFrog

Henceforth known as Mr Floppy
I just brandished a welding torch for the first time in about 15 years. 20 minutes of playing about with the old brompton seatpost and tweaking the settings and my technique. I started from the left in case it's not entirely obvious :blush::laugh::laugh:

View attachment 492028

View attachment 492029

Clearly theres more practice needed but I'm at least confident now that with some practice I can be reasonable at it, and that's all I'm really aiming for :laugh:

A few more bits have arrived but I'll post another update when more has happened. It's been a lousy week so hopefully I'll get more chance to play in the garage and forget about life for a while soon :laugh:
You know you’ve totally fecked that seatpost don’tcha?
 
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