Question #1 - How do I know when I'm getting low on gas. I think my gauge is showing like 400psi? Does that sound right? I can still hear it flowing.

Question #2 - what does it mean when your ---- starts to look like a 4th of July sparkler and the welds start to look like kinda deflated and often with a hole in the center of the weld when you let up?

Machine is a 110v Snap-On MIG (forget the specs)

 

Assuming the gauge is correct, they'll keep flowing abit after 0psi. Depends on how big the tank is. When gas coverage is going to become a problem, or you're working on something that can't handle a ---- up that needs to be ground & re-welded. That's when you swap tanks.

The ---- looking like a 4th of july sparkler sounds like porosity. You need to clean your ---- really well (no rust, or scale), have adiquate shielding gas, and use clean wire.
The hole in the center of the weld when you let up is a crater crack. When you go to end the weld you need to go to the end, then take a small back-step to fill in the end of the weld.

 

#2 is caused by #1 and the addition of paint/rust/dirt/grease/etc.

 

Question #1 - You'll know because you start getting porosity. the arc needs the shielding gas to "protect" it from the atmosphere or you get little gas pockets, aka porosity, although on that note you can get porosity from too much shielding gas as well.

Question #2 - if the "sparkler" effect you are talking about is the spatter produced when welding then you could have poor grounding, dirty material or possibly too large of a tip to work distance (arc length), current too high, etc.

Do you have pictures of your deflated welds? also is there only one hole in the centre or is it many little holes?

 

I'm a noob on a mig as well. i KNEW when i ran out of gas yesterday on my lincoln. my welds went from looking like decent noob bead, to a bunch of chicken ---- spatter, and poor penetration :[