Welding Chromoly Frame With Flux Core

[a.tab56]

Hello all,

I'm new to bike frame fabrication. I have a Lincoln flux core welder I split with a friend (I'm a college student). I'm wondering if I would have to only use mild steel or if I could use my flux core welder to weld prefabricated chromoly tubes? I've seen some information on the internet where people did some projects with flux core but then other saying that mixing dissimilar metals wouldn't be a good idea.

 

[Pondo]

Hello all,

I'm new to bike frame fabrication. I have a Lincoln flux core welder I split with a friend (I'm a college student). I'm wondering if I would have to only use mild steel or if I could use my flux core welder to weld prefabricated chromoly tubes? I've seen some information on the internet where people did some projects with flux core but then other saying that mixing dissimilar metals wouldn't be a good idea.

Welcome to the forum! I'm a novice welder myself. I've been welding on bike frames for small projects for a bit now with flux core and gas flux. Mild steel welds pretty nicely but I have trouble with chromoly blowing through. Not sure why but chromoly is trickier to weld. There are probably some good videos on welding chromoly but I haven't investigated it yet. Most of the vintage and dept store frames I weld are mild steel. Maybe some of the more experienced welders on the forum will weigh in. Make sure to post pics of your projects, we'd love to see them!

 

[Captain Awesome]

You can get adhesion using flux core on chromoly but the problem is that it doesn’t carry the tensile strength you want. Also with fluxcore you’re going to see a lot more HAZ as well as the spatter. The spatter can be cleaned up, but that heat distortion/uneven distribution is always a problem with fluxcore.

So can it be done, yes.

Are we just talking about some beach cruiser or what?

 

[Pondo]

I think TIG might be better for chromoly?

 

[Captain Awesome]

I think TIG might be better for chromoly?

100%

 

[a.tab56]

You can get adhesion using flux core on chromoly but the problem is that it doesn’t carry the tensile strength you want. Also with fluxcore you’re going to see a lot more HAZ as well as the spatter. The spatter can be cleaned up, but that heat distortion/uneven distribution is always a problem with fluxcore.

So can it be done, yes.

Are we just talking about some beach cruiser or what?

Its supposed to be a board track racer frame. I'm planning on using a Honda gc160 engine from a power washer. I'm wondering if I should build the jig and have a shop weld it all together for me. I'm not buying a tig welder and gas and I'm most likely not going to braze it.

 

[Captain Awesome]

Its supposed to be a board track racer frame. I'm planning on using a Honda gc160 engine from a power washer. I'm wondering if I should build the jig and have a shop weld it all together for me. I'm not buying a tig welder and gas and I'm most likely not going to braze it.

I would tack it really well with your flux and have it tig welded. They should be able to section weld it and grind out the flux tacks to be real conscientious

 

[DesmoDog]

No flames intended, but let me ask why are you wanting to use chrome moly?

It's harder to weld, it's no stiffer than mild steel, and no lighter than mild steel. If you simply substitute chrome moly for mild steel on your frame you will end up with a frame that's harder to fabricate but no stiffer and no lighter. It won't dent quite as easily though.

It sounds like it's your first frame. Go with mild steel, chromoly is wasted on the average builder. If you don't have a very specific reason for using it, don't.

If it were ME, I'd go with mild steel and a oxy/acetylene torch with bronze filler. Flux core is for field fixes when you can't get out of the wind IMHO...