Any welding specialists here?
 

If there's anyone with some knowledge of welding, could you take a look at these pics of my bike to see if the cracks are repairable?

The cracks are on the same part of the frame on each side of the bike, and unfortunately both cracks are going through the thread that holds bolts in place to allow for suspension movement. I've actually been able to ride the bike for the last couple of years with these cracks but one of them suddenly got a lot worse after a ride a couple of days ago, and i fear the whole thing could give way at any time now.

I've got no chance of spare parts as this model is several years old now and don't want the whole thing to become a write off as it's worth a few thousand pounds.

Here are 2 pics from each side, click for high res-

http://img8.imageshack.us/img8/5876/konabeara.jpg

http://img23.imageshack.us/img23/4066/konabearb.jpg

http://img23.imageshack.us/img23/8259/konabearc.jpg

http://img23.imageshack.us/img23/2368/konabeard.jpg

They are repairable, do you know what the steel alloy is, as that will be important for selecting the filler rod. There is also a chance it had post welding heat treatment.
I would suggest either contacting some of the local bike shops/clubs, specialist welders and/or the manufacturors of the bike.

hmm i think it could be rather difficult to weld.
aren´t bikes mostly made out of aluminum alloys ? (MIG welding would be needed then iirc)

TIG http://www.discussworldissues.com/fo...lies/wink1.gif

Are there any other cracks? It might not be worth it to weld it at one spot then another breaks.

I was an ASME certified welder.

I also worked as a Tig welder in a custom sport wheelchair manufacturing shop working with both aluminum, titanium, and steel materials.

Yes, those cracks are easily fixable. Looking at it, it appears to be aluminum (based on the colors of the material under the crack and the size of the existing welds, aluminum is larger, steel and titanium are small). Anyone with good aluminum TIG experience can do it. But be careful, out of all the welders out there, a low % of them out there actually know how to TIG aluminum.

I doubt they used any aluminum that is difficult to weld. Aluminum/Magnesium mixes and pot aluminum are extremely hard to weld, Cast aluminum can be difficult, but can be done. But usually they use plain aluminum for bikes, which is simple to weld.

I have a feeling it's classed as '7005 Aluminium tubing' that they use. I've had a check over the rest of the bike and it seems fine, it looks like the parts that have cracked are high stress points considering they are right at the back of the bike and on the inner side of the frame.

It may still have a sticker on the frame with the alloy spec' and heat treatment - if any.

You and Rizob are in the same part of the country, perhaps he can recommend someone?

MIG? ROFL dude. MIG is not for this kind of stuff. I'd say Low amp TIG and apprpriate filler would do otherwise good old ace/oxy gas welding if it's indeed aluminum.

edit : heat treatment/stress relieving is not neccessary.

Maybe MIG is something different in the US ?
I´m not a welder and i have to be honest that i haven´t done all that much welding (I´m a precision engineer/technician), So i´m not going to argue,
but i went through one of my books (Schweißtechnik - X65/1) and the first that came up when welding Aluminum alloys was MIG.
Allthough it all delends on the alloy i guess.

TIG - Tungsten Inert Gas you have a holder with a needle like Tungsten sticking out of it (3-5mm) and you feed filler with your other hand and the gas used is Argon. MIG - Metal Inert Gas again you have a machine and a holder and the filler comes out of the holder automatically (you can adjust filler feed speed) and the gas used is either CO2 or a mixture of CO2 (80%) and Ar (20%). Hope this makes sense i'm a little intoxicated.

I used to work for a Danish company and learned some of this stuff... Let me tell ya trying to weld a crack on a bike with MIG would be like trying to kill a fly with a sledgehammer. Too fast too powerful...

Using CO2 or CO2 mix is used when welding steel. When mig welding aluminum, you use Argon or Argon helium mix.

Stainless is different as you can pretty much get away with using any gas you want. However, ASME code specifies you must use 98% Ar/ 2% O2. But I personally like Tri-mixes when doing stainless, CO2/Ar/He.

A lot of time, it comes down to welders preference. For Tig welding, I preferred 90% Argon w/ 10% helium. It works for pretty much for all metals under tig, ie carbon, stainless, aluminum, titanium.

And you can MIG the cracks. Though TIG would be better, MIG would not be that difficult to do. There's an invention called Pulsed MIG that allows you to MIG thinner metals easier. And if you don't have a machine capable of pulse, a good welder can still use the MIG process on those cracks as long as he controls the machine well and doesn't do the weld in a single burst. He could do it with several short bursts without blowing the metal out.