Am welding up some benches for the shed with a BOC 250C MIG welder: BOC*MIG*WELDER*250C*Compact*240V*::*Mig*Welders*:: *Welding*Machines*::*Bob*the*Welder

Most of the stuff I am welding is 3mm (mild steel).

My 'cheat sheet' from BOC recommends 0.9 wire (OK), wire feed speed of 5 - 7 m/min (OK) 16-18 volts (OK) and 60-80 Amps (Not OK ).

The manual tells me the combination of switches to get 17 volts (Course voltage switch 1, fine switch 2).

So - how do the Amps get set if there is no switch for this.

Is it automatic because I have chosen the voltage and the wire speed?

Is there a formula to get amps from the voltage (V=I/R or something?, not that I know what the resistance is...)

Do I not need to worry about the Amps if I have set the voltage?

Thanks
David

Hi David

from memory when using the Lincoln Units at TAFE for 3-4 mm Mild steel
I adjust the voltage to Course = 2 Fine= 5-6 and wire speed about 3.5-4

keep playing around with the settings until you get the ideal wire speed and amperage.

course 1 and fine 2 may be a bit cold

The welder is 30 - 250 Amps, and I have:
o: Course voltage 'clicks' 1 - 4
o: Fine Voltage 'clicks' 1 - 4
so I'd be guessing that Course 1 Fine 2 is around 50 Amps (wild guess).

I have been playing around with various combinations even up to Course 3 Fine 3 but this is too high for 3mm steel.

Seems strange that they rate the welder by Amps, and give usage recommendations in Amps, but only have voltage controls

MIG are constant voltage - set to required voltage before you start to weld. Then amperage will vary depending how fast you are welding. Increase/decrease wire feed rate and current will automatically increase/decrease.

The current rating is duty cycle rating.

TIG and stick are constant current - set to required amperage before you start to weld.

__________________
John

So if my welds are sitting "on top" of the steel joints and not penetrating deep enough, should I be increasing the wire speed, or upping the voltage?

try upping the voltage or decrease the wire speed.
cheers
blaze

you need to get a feel for what ithe wire is doing, if the gun is jerky and the welds are splattering everywhere it needs to be hotter or have less wire going to the weld pool.
think of the noise sizzling bacon or what a large sheet of paper sounds like when you tear it, you need to replicate that noise.

to explain how to weld over the tinternet is hard, alot harder than getting someone to show you.

have a good look at youtube there are heaps of how to weld videos there.

cheers phil

David,

I have a 250R BOC MIG. I'll tell you what settings I would use, hopefully they should be close to what you need.

I would set it some were between 2-4 or 3-2 and play with the wire feed untill it is right, start about 5.

Keep in mind the values in the books for wire speed are not a good representation of what to set the machine. I hardly set mine over 6.

It should sound like a two stoke bike on power band. If it is pushing the tip back, drop the wire speed. If the wire is melting to far back towards the tip increase the wire speed.

Hope this helps,

Tim

You may need to go closer in to the job with the tip if you are not getting penetration. Remember in for penetration, out for fill.

The nice crackle of frying bacon is the common analogy to describe the aim for sound of MIg.

OK - I'll go and have another crack at things tonight when I finish work. Thanks for all that advice.

I have had the wire "balling" on the end and dripping off the wire to the weld (like globules of molten steel), and not a normal sound.

I know what you mean about "that" sound. When the sound is right you know the weld is going to end up nice. Practice, practice, practice.....

Makes you appreciate what a skill it is to weld properly. The good guys make it look so easy.