Poor penetration

[Holmefarmer]

Hi, I'm a relative newcomer to MIG welding, but have had some tuition, so I can lay down a decent looking weld. My machine is a german Erfi 700, which has a max output of 160 amps. It is a semi pro machine with fan cooling and a 6 step voltage controller, which automatically controls wire speed but with a fine adjustment available for the wire speed.
I am restoring a 1937 Morris truck, which need some substantial work on the chassis, which is 5 gauge, or 5.2mm thick, now rusted in most places to approx 4.5mm.
My problem is that even on max output and some (1/2 thickness) v-prepping, I am struggling to get full penetration. It is a single phase machine and I have checked that I am not at the end of a long extension lead, that the earth lead and the main connections inside are sound, and that the no load voltage at the machine is 240v plus.
I have adjusted the angle of the gun to vertical and adjusted the wire speed as high as I can, whilst keeping the arc stable, but still fail to achieve full penetration. Any suggestions apart from buying a bigger machine?

 

[shenion]

What size wire are you using?
Gas or gasless?

I use 0.9mm on anything over 1/8" (3.2mm)

 

[Holmefarmer]

Hi, the machine is using 0.8, the gas is Argolight. Thanks

 

[peterd51]

Hi,

my Clarke 150TE is 150 amps and can manage that thickness in one pass but I have to take it a bit slower than normal.

Also I'd be prepping it right down to the root.

But is there any reason why you need to do it in one? Could you prep it all the way down, do a root pass and then a capping pass possibly with a slight weave?

Regards
Peter

 

[Holmefarmer]

Hi, thanks for the suggestion. I will try that, but from previous tries, the "root" weld will fill the joint without a 2nd pass.