Brompton news!

[FrankCrank]

I do TIG welding here from time to time, for bike related and other domestic projects, so am biased when it comes to fabrication.
Last time I brazed was during my apprenticeship, mostly for repairs on the car, usual culprits - sills, top plates and floor pans.
Always thought brazing to give good results, and thought it strange at the time that it was no longer allowed for car repairs, indeed it would result in an MOT failure if used.

As to the Brommie application, I'd argue that more heat goes into brazing a joint, verses TIG. Brazing needs the joint area heated cherry red so as the filler will melt and form a strong bond. TIG is a more targeted thing, and although the actual weld is done at a higher temperature, it is only the weld that melts - if the parent metal turned cherry red then somethings wrong.

I'm certainly no expert in this field, and would be interesting to hear what professional welders would say on the subject.

 

[wafter]

I do TIG welding here from time to time, for bike related and other domestic projects, so am biased when it comes to fabrication.
Last time I brazed was during my apprenticeship, mostly for repairs on the car, usual culprits - sills, top plates and floor pans.
Always thought brazing to give good results, and thought it strange at the time that it was no longer allowed for car repairs, indeed it would result in an MOT failure if used.

As to the Brommie application, I'd argue that more heat goes into brazing a joint, verses TIG. Brazing needs the joint area heated cherry red so as the filler will melt and form a strong bond. TIG is a more targeted thing, and although the actual weld is done at a higher temperature, it is only the weld that melts - if the parent metal turned cherry red then somethings wrong.

I'm certainly no expert in this field, and would be interesting to hear what professional welders would say on the subject.

Your point about TIG might actually be the problem; causing high thermal (and hence stress) gradients in close proximity to the weld / areas of highest mechanical stress.

IIRC one of the reasons Reynolds 753 went the way of the dodo was because of its lack of tolerance to the higher temperatures encountered in TIG welded frames as the industry moved away from brazed, lugged construction.

That said, to contradict my previous point about heat treatment - I suspect Brompton frames probably aren't exotic enough to be heat treated so loss of temper probably isn't an issue... while stress concentrations could be.

It would certainly be interesting to hear from someone more knowledgeable on the subject - I touched on this stuff decades ago during my degree but it's all long-since lost.

I do have a TIG welder (bought for an ill-fated automotive project that predictably never happened) - I'd love to have the facilities to practice and really get good at it.. imagine having the ability to build one's own bike frame

 

[FrankCrank]

My guess is Brommies are made of chromoly, unless someone knows otherwise, so would be perfectly OK for TIG welding, and without heat treatment I believe. The clones are chromoly from what I gather, and TIG welded, so again not sure why Brommies are brazed. Got to be some other reason than simply looking blingy under a coat of varnish.

 

[Gunk]

I still don’t understand what they don’t just make them out of aluminium, import the frameset and just assemble them here.

 

[brommieinkorea]

I still don’t understand what they don’t just make them out of aluminium, import the frameset and just assemble them here.

Aluminum is only as strong as steel per pound. Alluminum's fatigue life is pitifully low compared to Steel.
Built in East Asia where the workers make £.5 / hour and live in squalor? That's a half pound an hour, just to be clear.
If things were equitable, no Asian bike would sell for over £50 with import costs.

 

[Mad Doug Biker]

Aluminum is only as strong as steel per pound. Alluminum's fatigue life is pitifully low compared to Steel.
Built in East Asia where the workers make £.5 / hour and live in squalor? That's a half pound an hour, just to be clear.
If things were equitable, no Asian bike would sell for over £50 with import costs.

Most modern train bodies (bear with me here) are made of aluminium.

At the Ladbrooke Grove accident (or was it Southall?), the 'Thames Turbo' (actually a class 165 DMU) was hit head on by a HST (Intercity 125. Class 43) at speed.
When the emergency services got there, they thought this 'Turbo' train only had 3 coaches.

Here's the kicker... It actually had had 4. The first coach had all but disintegrated on impact, causing a large loss of life!! 😱😱😱😱

Sobering stuff and why you should NEVER travel in the first coach (or possibly second, but, anyway).

 

[FrankCrank]

My preference would be steel for any type of folding bike. Can't offer scientific facts to back this up, just a gut feeling.
There are some aly framed examples coming out over this way, if that's your thing.

Pretty sure the steel frames here are all manufactured in the same place in China, then parts added by the various badged marques.
May be tempted to get a Bromptnot at some stage - just wish they'd innovate a bit instead of just cloning.
A version with 305mm fatter tyres and disk brakes would be nice. Might have a slightly larger fold, but not everyone needs a tiny fold, just portability.

My guess for the UK - frames (TIG welded) imported from China, and assembled somewhere other than the expensive south east of the country. The partnership with Decathlon makes good sense to me, they know how to provide quality at affordable prices.

 

[Fastpedaller]

My guess is Brommies are made of chromoly, unless someone knows otherwise, so would be perfectly OK for TIG welding, and without heat treatment I believe. The clones are chromoly from what I gather, and TIG welded, so again not sure why Brommies are brazed. Got to be some other reason than simply looking blingy under a coat of varnish.

TIG (or indeed any welding) involves melting of the parent metal, brazing does not. Steel tend to break just outside the weldpool in the heat-affected zone. If you take a look at most TIG welded frames you'll see an extra gusset added on the underside of the tube between the headtube and downtube. This is the part of the mainframe under the most stress, so the addition is there because without it the frame may fail.
A similar brazed frame doesn't have this sort of reinforcement - or of course it can have similar by way of lugs
The message here is that any material (within reason) can be used to make a frame if the design is correct and relevant testing is carried out, along with ongoing process quality control. I understand Brompton have good procedures in place, and will get to the bottom of what's happened in the G-Line failure reported.

 

[Gunk]

My preference would be steel for any type of folding bike. Can't offer scientific facts to back this up, just a gut feeling.
There are some aly framed examples coming out over this way, if that's your thing.

Pretty sure the steel frames here are all manufactured in the same place in China, then parts added by the various badged marques.
May be tempted to get a Bromptnot at some stage - just wish they'd innovate a bit instead of just cloning.
A version with 305mm fatter tyres and disk brakes would be nice. Might have a slightly larger fold, but not everyone needs a tiny fold, just portability.

My guess for the UK - frames (TIG welded) imported from China, and assembled somewhere other than the expensive south east of the country. The partnership with Decathlon makes good sense to me, they know how to provide quality at affordable prices.

Just over £500 for a knock off steel framed S6L on AliExpress. Shows how cheaply they can be made, although I’ve never actually inspected one close up, be interesting to compare against the real thing.

 

[FrankCrank]

Just over £500 for a knock off steel framed S6L on AliExpress. Shows how cheaply they can be made, although I’ve never actually inspected one close up, be interesting to compare against the real thing.

View attachment 814268

I've seen them on sale for as little as £400, but pretty sure there'd be tax and import duty added on. Gotta be a dozen or more similar brands now - epicentre seems to be Singapore. When you see what a new, original Brommie costs here, it's a no brainer why clones are so popular.