Welding Chromoly Frame With Flux Core

[DesmoDog]

This seems to imply less strength.

I'm not looking for an argument either but no, comments on stiffness have nothing to do with strength. Stiffness and strength of a material are not interchangable, one does not follow the other.

4130 chromoly = same strength for less weight. Which includes stiffness and other factors.

No, strength does not include stiffness. A thinner walled chromoly tube will be less stiff than a thicker walled mild steel tube of the same OD. Which doesn't really matter here when we're talking about a first time builder with a flux core welder so I'm not going to go on about it, but you can look it up if you don't believe it.

We're obviously getting way into the weeds here and contrary to how it may appear, I'm not wanting to argue about it either.

The point was to not decide on a material based on probable misconceptions about the benefits a home builder with a flux core welder might see.

 

[SkyknightJohn]

Perhaps I was confusing stiffnes with the modulus of elasticity and yeild strength… mild will deform when 4130 will spring back to shape, at a given force above mild’s yield. That is desireable is some applications, but not the same as stiffness. My brain probably went “doesn’t bend as easily=more stiff.”

Titanium on the other hand…
Also not for the hobbiest or home builder with flux core.

I think we’re all agreed that mild steel is the way to get started for the OP with their setup.

 

[DesmoDog]

titanium...

I had a program at work where we used it. OEMs were looking for weight savings so I had what was basially a cat-back system made for a Jeep Cherokee. All one piece, no clamps. It weighed something like 6.5 lbs but it flexed like a, um, something pretty springy.

Mounted it on a vehicle, drove it all winter, took it off in the spring and after hosing it down it looked just like new. Well, almost. The welds looked as new anyway. It never did go into production obviously but gave us experience working with titanium.

I ended up with a couple small sheets of leftover matierial. When I moved I put it in my dad's shop. My mom was cleaning up one day, saw it, and threw it away because she figured it was just more scrap steel my dad had around (he had passed away by this time).

I came looking for it a little while later. She apologized, told me she had thrown it out and offered to buy more if I needed it.

I told her don't bother, not important... and never did tell her what it was. She virtually NEVER does stuff like that and she would have been heartbroken had I explained it.

Easy come, easy go... I would have just wasted it on something stupid anyway.

 

[Captain Awesome]

titanium...

I had a program at work where we used it. OEMs were looking for weight savings so I had what was basially a cat-back system made for a Jeep Cherokee. All one piece, no clamps. It weighed something like 6.5 lbs but it flexed like a, um, something pretty springy.

Mounted it on a vehicle, drove it all winter, took it off in the spring and after hosing it down it looked just like new. Well, almost. The welds looked as new anyway. It never did go into production obviously but gave us experience working with titanium.

I ended up with a couple small sheets of leftover matierial. When I moved I put it in my dad's shop. My mom was cleaning up one day, saw it, and threw it away because she figured it was just more scrap steel my dad had around (he had passed away by this time).

I came looking for it a little while later. She apologized, told me she had thrown it out and offered to buy more if I needed it.

I told her don't bother, not important... and never did tell her what it was. She virtually NEVER does stuff like that and she would have been heartbroken had I explained it.

Easy come, easy go... I would have just wasted it on something stupid anyway.

I have a similar story but it was inconel. A former acquaintance made all the exhausts for Panther racing and gave me a bunch of tubing drops. My derelict brother took it to the recycling center for beer money thinking it was aluminum

 

[us56456712]

I used stick, flux core wire without gas and a few brazed joints on this hack bike frame. Mild steel. It’s harder to do than you think.

Before jumping in on your project I would take two or three old mild steel frames, cut off the rear triangles and swap them. One should be a woman’s frame and you can use a top tube swap to make a gender bender. This will give you experience coping the tubing to fit the tubing angles and length. This was my first experiment doing a bike frame using this method. The front half was originally a woman’s frame. I never welded before this. I used it on trails for most of a summer before one of the welds broke. The top tube was filled with sand, put into a large wood heater to get it red hot and then bent, holding it with vice grips, over an old car rim.