WELDING A BIKE FRAME

[SKYBOW]

I'm trying to modify a mountain bike frame. How do I join the two pieces of tubing? I don't want an accident while going down the road.

 

[SKYBOW]

I forgot to tell you guys that I have a Lincoln Dialarc 250 stick welder AC?DC and also a Oxy/act torch. What process? would be the easiest but still be safe?

 

[old]

Its probably made from some sort of alloy and will be very hard to weld

 

[Anonymous-0]

kid tried that and that crap will not weld

 

[jose bagge]

What brand of bike? I'm assuming it's not aluminum- so if it's a decent bike it's probably chrome moly or another alloy that frameset builders called "Trutemper". If it's steel, your best bet is to braze it. All the "high end" steel mountain bikes like Ritchey, early Specialized, etc were brazed.
If it's an "inexpensive" brand, I'd still braze it- very thin wall stuff.
Here's a cool fact about the steel tubing used on early "high end" bikes- it had thicker wall thickness on the ends where you would mate tubes together. Real high end stuff had "lugged" frames (external joints) and they would sweat the tubes together like copper plumbing tubing. On racing bikes they would trim the lugs down to almost nothing, very artistic.
I just made my kids a tandem bike out of landfill junk- lotsa fun to fool with...

 

[Anonymous-0]

Brazing would be a good bet. Make sure to clean everything really good down to bare metal. Brazing doesn't actually melt the material your joining. It does open the pores in the metal for the brazing rod to hold though. Some bikes are TIG welded and some cheaper bikes are even MIG welded. Aluminum frames are TIG welded. How is the rest of the bike joined? I watched an episode of "How it's made" about bikes. It showed CCM bikes being brazed but not the conventional way. The had a ring of the brazing rod inside the tubes to be joined and applied heat after everything was set up in the jig. The heat melted the brazing material and it flowed around the joint. Kind of like soldering copper pipe. Brazing is hotter and stronger than normal soldering. Silver soldering is very strong but a lot more expensive to do.

 

[Anonymous-0]

If you are doing a butt joint and plan to braze it... you might consider slipping a smaller piece of tubing that fits tight, into the two halves you will braze. Cut your butt pieces to leave an 1/8" gap that will expose the smaller tubing. Braze away. Good Luck,

 

[Don L C]

Oxy/act.and brass/flux rod......

 

[Tim B from MA]

Reminds me of the time when I was an adolescent, my brother, I and a friend cut the forks off junk bikes and bolted them to the ends of the forks on our bannana bikes to make "choppers".

Riding down the road, my friend and I stopped to wait for my bother pedaling furiously down a long low hill, trying to catch up when....

The added-on forks came off and the front wheel along with them. He looked just like SUPERMAN flying through the air. Funny as heck, fortuanately he didn't get hurt too badly, mostly skun-up hands and pride.

 

[Jim k]

Yea I did that when I was a kid bolted two sets onto the bikes forks, going down a hill built up too much speed and it developed the death wobble. My extensions abandoned ship and the factory forks dug into the tar and launched me about 30'. You'd a thought I slid down the road doin about a hundred miles an hour from all the road rash I had.
I also had a Shwinn 5-speed that looked just like a 10 speed. that bike was ballanced perfectly, I could ride a wheelie for quite some distance with it. I also liked to jump it, Evil Knevil was popular. I would get 5 or 6 friends to lie on the ground and I would jump over them
I only landed on one of them once but that was because he moved.

 

[Anonymous-0]

As NIndiana Dan says. The inner tube will give it strength.

 

[T_Bone]

Hi Skybow,

Before we can recomend a welding process we need to know what metal the frame is made out of? Flip the bike over and pick a spot that's easy to repair then grind a small spot to bear metal paying close attention to the spark color and patteren then drill a small hole in the tube and look at the cuttings of the metal grain thru a 10x loop.

Online you will find several websites that describe with pictures the different color sparks that metals make along with what the grain structure looks like in a 10x loop.

The frame mfg might also post this info.

Then we can say for sure how to weld it and the correct joint design needed. Without that, were just guessing.

T_Bone

 

[Little Ed]

Use the oxy torch with a steel oxy rod, if it is a steel frame. Do not use a brass rod on steel, you will have trouble with the brass cracking. Use the tube in a tube method described above, but leave a big enough gap that you can get the weld on the inner piece as well as both tube ends. It is a skill well worth learning. I would prefer tig, but if you got the torch use it. It makes a great weld on thin material.

 

[Anonymous-0]

It will most likely look like the sparks from 4130.All those fancy racing frames are TIG welded chrome moly.On a motorcycle frame when you cut a tube you put a sleeve inside to have something to weld to.If you need a bunch of cuts of 4130 for practice welding you can get it from AIRCRAfT SPRUCE and SPECIALTY Its called chrome moly practice weld kit[or cut offs].They sell longer too.It was about 15 bucks for 1 ft cuts to practice on.This job may be best subbed out to a weldor.

 

[jose bagge]

google the name SHELDON BROWN for all things bicycle- this guy is the "monster garage" of bikes. Forget all the welding nonsense- BRAZE IT. If it was good enough for Tom Ritchey, i guarrantee it will be good enough for your needs!

 

[jose bagge]

The process you are referring to is called "furnace brazed"....all the italian frames of old were externally lugged and furnace brazed...pretty stuff

 

[dave guest]

BTDT Braze

 

[Fred Martin]

If it's ferrous metal I would use silver solder. It has the best capillary attraction of all the brazing type rods and the strongest.My opinion... ohfred