This weekly video is on tig welding tubing... thin wall steel tubing.
What kind of steel is this tubing made from ? I dont really know except that it seems to weld a lot like a plain carbon steel and that it is used for custom bicycle frames .
According to Mike Zanconato of Zanconato Cutom cycles ( thanks for all the help Mike!!) "Compared to 4130, this alloy has about half the carbon and chromium
content that 4130 does, but it has about 3 times more manganese and also
vanadium added. This allows the wall thickness to be reduced to 0.016" in some cases. "
The manufacturer of this thinwall steel tubing recommends using weldmold 880 tig rod because it provides excellent strength and elongation properties.
Elongation is basically how much a weld will give or stretch before breaking.
You want welds on bicycles to have a bit of stretch to them.
So using the rule of 33 ( thats my rule and its not really a rule...just an easy way to remember pulse settings that work) I set the pule rate to 33 pulses per second, and I set the background current to 33%, and the % on time also known as pulse width to 33.
Because thin wall tubing can be hard to weld if it has any gap in the fitup and pulsing at 33pps allows a bit of time before a hole is blown. It gives me an extra second to get the rod in there when I see that I am about to melt a corner off, blow a hole, etc.
There are plenty of bike builders who never use pulse tig because pulse is not absolutely needed. But I just like it on thin stuff. I think it helps.
Another tig welding technique that helps is to back up the arc while you are adding filler rod.
On thin metal, if you move the arc ahead too far, wait too long, dont add filler quick enough....you can have a hole quickly.
Backing up the arc while you add filler puts the arc over a thicker area that is less likely to melt away.
So which rod is better? ER70s-2 or Weldmold 880?
I think I would have to say the weldmold 880 rod was more fun to weld with. It was prettier and flowed like honey.
But does that make it better?
But both rods passed the hammer test and ER70 tig rod is very cheap and works just fine for tig welding chromoly tubing as well as other alloy steels like the tubing welded today.
I would feel safe riding a bike made from this tubing welded with either rod.