Instructables

Step 4: Prep for Your Weld

Before you start welding make sure things are properly setup at both the welder and on the piece you are about to weld.

The Welder

Check to make sure that the valve to the shielding gas is open and that you have around 20ft3/hr flowing through the regulator. The welder needs to be on, the grounding clamp attached to your welding table or to the piece of metal directly and you need to have proper wire speed and power setting dialed in (more on that later).

The Metal

While you can pretty much just take a MIG welder, squeeze the trigger and and touch it to your work piece to weld you won't get a great result. If you want the weld to be strong and clean, taking 5 minutes to clean your metal and grind down any edges that are being joined will really help your weld.

In the picture below randofo is using an angle grinder to bevel the edges of some square tube before it gets welded onto another piece of square tubing. By creating two bevels on the joining edges it makes a little valley for the weld pool to form in. Doing this for butt welds (when two things are pushed together and joined) is a good idea.
 
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Make sure the area where your grounding clamp is attached is free from rust so that it can make good contact. Otherwise, it will arc and chew up your nice $20 grounding clamp and produce poor welds.
do you have to clean the material when you weld with a mig and no gas.
MIG stands for Metal Inert Gas. Wire welding can also be done with gasless flux core wire, if that's what you mean. Welding should always be done on clean metal, no matter what the process. The black mill scale and rust are pretty easy to remove with an angle grinder. Plus, a nice angle grinder is a lot cheaper than a welder. Once you get one, you won't know how you did any welding without it.
 dont forget to get the no gas type flux core as well... some places will try sell you the dual shielding type... if you use the dual shielding type with no gas you will get lots of spatter and a okay looking of a weld.... pretty much alot of cleanup when your done :(