Step 2: How the Machine Works

Picture of How the Machine Works
mig cross section.jpg
A MIG welder has a couple of different parts. If you open one up you will be able to see something that looks like what is pictured below.

The Welder

Inside the welder you will find a spool of wire and a series of rollers that pushes the wire out to the welding gun. There isn't much going on inside this part of the welder, so it's worth it to take just a minute and familiarize yourself with the different parts. If the wire feed jams up for any reason (this does happen from time to time) you will want to check this part of the machine out.

The large spool of wire should be held on with a tension nut. The nut should be tight enough to keep the spool from unraveling, but not so tight that the rollers can't pull the wire from the spool.

If you follow the wire from the spool you can see that it goes into a set of rollers that pull the wire off of the big roll. This welder is set up to weld aluminum, so it has aluminum wire loaded into it. The MIG welding I am going to describe in this instructable is for steel which uses a copper colored wire.

The Gas Tank

Assuming you are using a shielding gas with your MIG welder there will be a tank of gas behind the MIG. The tank is either 100% Argon or a mixture of CO2 and Argon. This gas shields the weld as it forms. Without the gas your welds will look brown, splattered and just generally not very nice. Open the main valve of the tank and make sure that there is some gas in the tank. Your gauges should be reading between 0 and 2500 PSI in the tank and the regulator should be set between 15 and 25 PSI depending on how you like to set things up and the type of welding gun you are using.

**It's a good rule of thumb to open all valves to all gas tanks in a shop only a half turn or so. Opening the valve all the way doesn't improve your flow any more than just cracking the valve open since the tank is under so much pressure. The logic behind this is so that if someone needs to quickly shut off gas in an emergency they don't have to spend time cranking down a fully open valve. This might not seem like such a big deal with Argon or CO2, but when your working with flammable gases like oxygen or acetylene you can see why it might come in handy in the event of an emergency.**

Once the wire passes through the rollers it is sent down a set of hoses which lead to the welding gun. The hoses carry the charged electrode and the argon gas.

The Welding Gun

The welding gun is the business end of things. It's where most of your attention will be directed during the welding process. The gun consists of a trigger that controls the wire feed and the flow of electricity. The wire is guided by a replaceable copper tip that is made for each specific welder. Tips vary in size to fit whatever diameter wire you happen to be welding with. Most likely this part of the welder will already be set up for you. The outside of the tip of gun is covered by a ceramic or metal cup which protects the electrode and directs the flow of gas out the tip of the gun. You can see the small piece of wire sticking out of the tip of the welding gun in the pictures below.

The Ground Clamp

The ground clamp is the cathode (-) in the circuit and completes the circuit between the welder, the welding gun and the project. It should either be clipped directly to the piece of metal being welding or onto a metal welding table like the one pictured below (we have two welders hence two clamps, you only need one clamp from the welder attached to your piece to weld).

The clip must be making good contact with the piece being welded for it to work so be sure to grind off any rust or paint that may be preventing it from making a connection with your work.

BornOnFire4 years ago
In regards to Gas Tank Regulator Valves, An oxygen setup should always be opened completely so as to seat the stem of the valve against the packing. Failure to seat the internal stem's packing will likely cause a leak-resulting in a potential large scale explosion. The potential of a leak is more common than one would think. Imagine your garden spigot that you water your pansies with. Open it all the way and it usually works fine. Turn it a just few times and, usually, it drips-not a big deal. It's just a little water right? Apply this situation to your stuffy garage. You are welding a few things and the phone rings. 30 minutes later, your garage is a blasting cap just waiting for ignition. You get back to your work, strike an arc, and all of a sudden, you see a white light and your late grandmother welcomes you "Home" into God's kingdom. Now, we all would like to see Grandma again but I'm sure she can wait a few more eternities before you show up. Now, I'm not saying all regulator setups will blow you into grandma's arms again, but the Oxy-Acetylene setups are potential fatalities- now you know.
massmale994 years ago
Hi all I am a non pro welder but to answer the question about getting shocked
from touching the table or any part of the pieces to be welded together no shock will occur just do not touch the bare welding wire and the tip with bare hands as you will feel some current and the same as when putting new wire in the machine don't touch the machine and any bare metal wire part when loading a new roll
especially around the roller feed as you will feel current again. I have been bitten a few times it is not at all very uncomfortable but it is still a little shock that surprises you and always do wear welding gloves not some cheap leather gloves real welding gloves they are thicker leather and have a longer cuff that protects your arms and wrist from getting flash burns from the arc and if you mess up and touch the hot welded metal been on the receiveing line a time or 2 not thinking and just reaching will get you a good burn and do always use the welding mask no blind welds save your eyes from sparks and arc flashes is a must there are a ton of other things but you will learn as you go
weld on dudes happy happy joy joy
TBC065 years ago
 a little note to add to the roller tension shouldn't be too tight to crush the wire... and to use the right liner for the type of wire your using
danmst3k5 years ago
Great instructable! I just got a welder from Harbor Freight. It's a 90amp wirefeed flux core for $63 after using a 20% off coupon along with a sidewalk sale(reg $149.99 on sale for $79)!!! But, anyway, I haven't tried it yet and still need to learn a few more things. One question I have is what happens if your bare skin makes contact with the welding table or the piece of metal you are welding. Can you get a shock from that? I know, it's probably a dump question but I haven't seen it addresed anywhere. Thanks.
dla888 danmst3k5 years ago
Yep, I'd be willing to bet that you would be on the recieving end of a large and painfull shock. Basically MIG welding is a big electrical circuit and if the table is metal it will conduct electricity.
vr4izm6 years ago
can you mig weld without the gas?
you can run flux-core wire through a GMAW(Gas Metal Arc Welder) MIG, welder, your technically your SMAW (Sheilded Metal Arc Welding) then. Flux-core is a lot more splattery and makes uglier beads and is more likely to break though.
dmcodwhy6 years ago
From my teachers "always open your valves all the way". The valves are designed with a seal at 100% open too. (as cox_gene said)
Great Instructable! I appreciate you taking the time to put this together :P
cox_gene6 years ago
opening the tank valve only slightly will be fine for argon or co2 or any welding gas, however it should not be used as a rule of thumb for all gasses. Oxygen, for example, is bottled at such a high pressure, the tank includes a double seated valve that only seals in fully open or fully closed position. any other position leaves the valve prone to seepage, and perhaps explosion. consult your gas supplier for individual gasses
shamuslauer7 years ago
what angles would u want the gun to be at?
dpocius8 years ago
Re: opening tank valve half a turn: I was taught that, for any valve, gas or liquid, even if you need to open it all the way, always back it off the full-open stop a quarter-turn or so. Two reasons: 1) The valve won't get stuck in the full-open position like it might if run hard onto the full open stop; B) You get immediate tactile indication of the valve's status. Loose handle means open (not evident if the valve is jammed tight open), tight handle means closed.