[cj737]

I've been fabricating a swing arm for a pal's vintage road race bike from CroMo (1"x2"x0.083 rectangular). Machined a nice pivot tube for him from 1.375x.375 to run a Ti pivot bolt through some bronze bushings (reamed and fit). Anyway, everything was calm seas and bright skies, until I was running a light cover pass over some miters in the leg. As the welds cooled, I noticed what I thought to be hairline cracks. What the Ef? I said.

I examined every weld I could at different stages for full penetration on the butt welds, and know I was solid there. Ground the weld flat to inspect the root. Yep, light crack (or so I thought). I dragged the arm up to a buddy who builds spec Car chassises. We did the good old dye penetrant kit. Phew!

Turns out, they were only porosity. But the cause... I learned was 2 fold: I was running a lot higher CFH than ideal (15-18 with a #8) AND, I was using my Ar/He mix bottle. I was told by a guy who does this for a living with plenty of Nascar wins on his chassises, don't use He mix with CroMo. Tends to want to make the weld area brittle. Who knew? (Well, probably many of you did, but I did not). And for anyone who happens along and doesn't know, now you do as well.

So, every day you weld, you can learn something new. The He mix was more an oversight than an intention. I just hadn't thought about it and cranked the knob on the tank connected. Swapped my hoses, finished up, Buttercup! Just when you started to think you knew something about anything, you learn you don't know half as much as you hoped you did.

[LtBadd]

Interesting, never heard that before.

Was this mix what you typically used for AL? I'm guessing so, you had it hooked up and just went with it on the CroMoly?

[cj737]

Yep. I just default to using it even on mild steel. In my life, sometimes from one moment to the next I'm switching tasks and in this case, I simply never even thought about it.

[BillE.Dee]

CJ, thanks for that info. I do the same thing with the different buttons on my welder. Put in some settings and not paying attention just move from one project to another and end up scratching my head in wonderment. I did recently read somewhere that different gas makes things happen...after hot dogs and beans, I can empty a new york city cab in 3 seconds. Different gas ya know??

[cj737]

CJ, thanks for that info. I do the same thing with the different buttons on my welder. Put in some settings and not paying attention just move from one project to another and end up scratching my head in wonderment. I did recently read somewhere that different gas makes things happen...after hot dogs and beans, I can empty a new york city cab in 3 seconds. Different gas ya know??

Not a gas “mix” I’m interested in using on steel, ally or CroMo