Arc welding a bicycle frame

[Wozzaaah]

I'd say it's probably inversely proportional!

Yeah, yeah. I'll get my coat.

It would depend on the trajectory, if the UHU'd stem failed at the same time then the trajectory would be low so time for very few ee's but if it held up then the trajectory would be higher meaning more ee's could be emitted before the inevitable 'smeck'.

(I'll get mine too )

George, I'll split this thread in a bit, I'll move Paul's posts to another thread.

 

[chunkolini]

To the ridiculers I say we must not forget of course that George could well represent the future of the human race.

That maverick strand of DNA that does things because they have to be done, like the first penguin to jump in the water, why did it happen?
The first salmon to head to sea?
The Montgolfier brothers to fill a bag with hot air and hang onto it?
None of them superficially rational acts.

Without this DNA we would still be wearing bunny skins and living in caves.

Sadly a lot of carriers of this gene end up in the International Darwin awards, but without them where would we be?
Respect to those who ascend over mediocrity.

Chunko'.

 

[GeorgeB]

To the ridiculers I say we must not forget of course that George could well represent the future of the human race.

From my point of view, I'm trying to return to basics, using my own common sense rather than being controlled by health and safety considerations which I think have gone too far.

Of course, when an amateur like me walks into an area which is someone else's specialist field (hobby or professional) then it's not surprising I face contempt and a certain level of ridicule. Specialist cycle shops speak to me like that when I ask about something a little out of the ordinary. Their best solution might be to point to a new bike costing about £800 or a new 'branded' handlebar stem costing £60, covered in fancy graphics. When I ask if they have basic components costing a lot less, they lose interest.

A bike is about as simple as something can get but its complexity seems to be exaggerated by the trade in an attempt to earn more money out people.

 

[the snooper]

Specialist cycle shops speak to me like that when I ask about something a little out of the ordinary.

at that point it time to walk if they cant be botherd to talk to you properly and take your custom elsewhere

 

[pedrobedro]

I think part of your problem is probably your location. If I walk into my local bike shop and ask for a handlebar stem they automatically start with the lowest price option (I think they know me ) and usually offer me several options to try to keep the cost down. I went in last week for a brake cable and it cost me more to get to the shop than the £1.69 I spent in there.

 

[hotrodder]

As said sounds like you need to find another shop and if we're talking central London then many of 'em are unfortunatly more interested in the 'hard sell' than helping someone out. Helpful ones do still exist though as well as there being some geared up more to keeping old bikes on the road than selling the latest, lightest gadget.

As i said it'll depend whether your handlebars have an oddball diameter where the stem clamps 'em but there are plenty cheap stems available regardless of location...

£14.99 for example from here. First thing you need to do is determine the diameter of the handlebars where the stem clamps them i.e. measure with a vernier caliper or take the bars to someone with a vernier or micrometer

 

[GeorgeB]

As said sounds like you need to find another shop and if we're talking central London then many of 'em are unfortunatly more interested in the 'hard sell' than helping someone out. Helpful ones do still exist though as well as there being some geared up more to keeping old bikes on the road than selling the latest, lightest gadget. As i said it'll depend whether your handlebars have an oddball diameter where the stem

Thank you again, for your help - all of you. Yes, I need to find a shop interested in keeping old (basic) bikes on the road, rather than selling mostly esoteric gear.

I think the diameters are fairly standard. I measured about 22mm for the riser tube so I guess that's the standard size of 22.2mm or whatever. I believe the handlebars are an inch so there's no problem finding a stem. That's the two components I'd need - a riser converter tube and a stem - to avoid threading the handlebars through an old style quill stem. Even at lowest cost, that's still £20 and I think they would be heavier. It's tempting to try and bond the old one together with resin but I know it's a bit of a gamble. If it doesn't work, the handlebars will be covered in resin and will probably be unusable. I doubt if it would crack, as in sudden breakage - it's more likely to come apart slowly, if it ever fails.

It seemed so straight forward to zap it with some welding until you pointed out it's an alloy, rather than pure aluminium. Can't one weld alloys like that?

 

[Archie]

George, almost all aluminium is an alloy. It is rare that aluminium is used in its pure state. One of the first was Duralumin which was developed for aircraft but not there are hundreds upon hundreds of alloys. 6000 series alloys are popular for things like bikes. In fact Wikipedia says 6061 specifically is common. Interestingly from your point of view it says that it is highly weldable which is no doubt true. However, it goes on to say that an approx. 80% loss of strength can be expected due to the welding process. If that weren't bad enough the problem with parts such as the stem you're looking at welding is that they are often sintered. Basically powdered metal is compressed and heated in a mould so that the grains bind together. It works brilliantly but the result is porous. The same can be true of cheaper castings. When you weld the trapped air pockets heat, expand and try to escape and that's when you end up with a foamy looking weld with no strength.

 

[GeorgeB]

George, almost all aluminium is an alloy. It is rare that aluminium is used in its pure state.

You're a mine of information! I didn't realise that when one reads about the TIG or MIG welding of aluminium, that's really about an aluminium alloy. I dropped the idea of welding after the previous warning. I don't doubt it would end up as a really ugly lump if I attempted a weld but could it be strong enough? My view is that resin will be stronger and more predictable. I'm kicking myself for vandalising the component in the first place.

 

[Archie]

It could be strong enough but then again it could not. It's not something I would do because a. I'd expect the weld to be pretty dodgy and b. it would look like an ugly lump!

Regarding 'glueing' I've really no idea. What 'resin' are you planning to use? What I do know of metal bonding is that the adhesives normally used are pretty ferocious chemicals and that surface preparation is absolutely key to a good join. The problem with a cracked part like the one you have is that cleaning it satisfactorily is next to impossible. Add to that the fact that the material is likely porous and will absorb greases etc. and my opinion is that you'd be looking at a very, very unsound join. It's not like there's a big contact area either. The only plus side is that if you try it you'll probably find out that it hasn't worked very quickly!

 

[Alfaman]

Morning All,

George, I found these two stems I have spare. Don't know if they will be any good to you, as they are this type (photo off Wikipedia), i.e. the stem clamps onto a 26mm dia steerer tube. They are steel.

 

[GeorgeB]

It could be strong enough but then again it could not. It's not something I would do because a. I'd expect the weld to be pretty dodgy and b. it would look like an ugly lump! Regarding 'glueing' I've really no idea. What 'resin' are you planning to use? What I do know of metal bonding is that the adhesives normally used are pretty ferocious chemicals and that surface preparation is absolutely key to a good join. The problem with a cracked part like the one you have is that cleaning it satisfactorily is next to impossible. Add to that the fact that the material is likely porous and will absorb greases etc. and my opinion is that you'd be looking at a very, very unsound join. It's not like there's a big contact area either. The only plus side is that if you try it you'll probably find out that it hasn't worked very quickly!

I agree with you about the likely outcome of any attempt at welding, which is why I think welding is a non-starter for this job. I'm so penny-pinching, I don't want to buy new parts but that's the obvious solution. I don't want a replacement quill stem because I won't be able to thread the handlebars through, without taking them apart.

Resin strikes me as feasible because of the huge contact area. The joint, handlebars and everything can be totally submerged in resin with kevlar or carbon fibre reinforcement to hold it all together. The final appearance will look chunky and unusual but could be made quite smooth and sufficiently strong. I'd never again be able top separate the handlebars and stem, but that doesn't matter.

 

[mike os]

my take on the stem


replacement stem £10-20

proper adhesive system... will need a consult with the manufacturer, rigorous preperation, probably a UV/HF oven cost????? I would guess more than the project to date given the part I would guess no one would want to touch it.

Over the counter adhesives are almost guarenteed to fail given the location & use, my guess is it will fail when the bar clamp is tightened..... unless you plan to glue that too?

Dental care... replace front teeth/ broken bones or brusing/contrusions..... £ teeth what say..£80-120 each?... maybe a week off work, or more.

Is is really worth the risk with something so critical, relatively difficult to repair & so cheap to replace?

As for the rest of the build...i dont think you will have any real problems... but I am not a bike expert like chunko. I appreciate the desire to reuse, repair & recycle, but there are sensible things that need doing & other stuff you can play with with relatively low risk

 

[Mikey D]

Goerge why not just join your local freecycle or freegle {or whatever its called} surely an endless supply of old bicycles ad no need for bodged repairs...

regards mike

 

[GeorgeB]

Goerge why not just join your local freecycle or freegle {or whatever its called} surely an endless supply of old bicycles ad no need for bodged repairs..

Good idea - but having started on this frame rebuild, I want to finish it!

Top end, esoteric cycle parts (and racing cars, etc) tend to made of carbon fibre for its incredible strength and other advantages. That's only carbon fabric and epoxy resin, I believe. Now there's expertise in forming a structure but I hope to figure that out. It's easy to wet glass fibre cloth with resin but I seem to recall someone on here say that carbon fibre is much more difficult to use. Is it? Does anyone else have experience of using carbon fibre fabric with epoxy resin?

alfaman - thank you again for your kind offer but steel is too heavy.

 

[Alfaman]

No probs George.

Wetting glass cloth is dead easy, just use the appropriate resin/hardener and stipple it in well with a chopped-down paintbrush.

Carbon fibre matting is a real sod to work with, plus it's really expensive! Although a company advertise in PPC magazine who sell CF starter packs, about £35. www.carbonmods.co.uk

 

[GeorgeB]

Wetting glass cloth is dead easy, just use the appropriate resin/hardener and stipple it in well with a chopped-down paintbrush.
Carbon fibre matting is a real sod to work with,

I've never seen carbon fibre fabric. Why is it difficult to work with, compared to glass cloth? Is kevlar any easier?

 

[Alfaman]

Sorry for the DP, but a quick tip that members might find useful if working with glass cloth.

Before applying the resin, get the item set up with a heavy-gauge PVC bag or similar, seal the job up round the edges and gaffer-tape a suitable nozzle for your hoover into the bag.

Once you have stippled the resin in well, seal the bag and attach your hoover and get all the air sucked out, then either clamp off the hose or just leave the thing running. Once it's cured, it makes a big difference to the strength and finished appearance with all the air bubbles gone.

 

[Alfaman]

Why is it difficult to work with, compared to glass cloth?

It's a swine to cut without dragging the weave, although there are different types (pre-preg) which are a bit easier. It's difficult to get it to wet, and always wants to lie the wrong way around the job

I did a year at Uni in the Prosthetics and Orthotics, where we made upper/lower limbs cups out of CF, and it's a steep learning curve!

Don't know much about Kevlar, sorry, except that it's also expensive!

 

[GeorgeB]

I looked at a 'how to' video on youtube and they make it look easy:

http://www.youtube.com/watch?v=IAdVO8Rkv6c

Nevertheless, as you say, carbon fibre is expensive and probably overkill for my bicycle. I'll use basic glass fibre.