I am new to Jeeps. Always loved them, always wanted one. Recently I purchased a 1986 CJ-7 partially completed project and am planning to completely rebuild it. I also own and operate a Machine & Welding shop and have been welding for around 20 years. We work on everything from simple repairs and fab work to large projects like derrick masts for oil service equipment that need to be magna-fluxed and x-rayed.
I'd like to throw my 2 cents in and give you some pointers. With Mig (GMAW) welding cleanliness is everything. Most of the steel you will buy has mill scale on it and this can have an effect on the quality of the weld. Usually you will want to remove the mill scale and get to the bare metal you will get a cleaner weld with less spatter. You can remove this with a grinding wheel or in a lot of cases just use a wire wheel on your angle grinder.
That pretty much pertains to any welding process,any oil,grease,mill scale,dirt,,etc can and will cause perosity and lack of fusion unseen
A bit about technique
When welding steel with a mig you will always get your best welds in the flat position. Assuming you are welding two plates at 90 degrees to each other and you are doing a fillet weld you have two directions to position your gun while welding. Up and Down / Left & Right. In the up and down position you want to have your gun tip at a 45 degree angle to the material. There are sometimes when you would want to raise or lower the gun to change angle like if you are welding different thicknesses of metal and you want to concentrate the heat on the thicker piece.
The second , left/right , direction is usually controlled by rolling your wrist to rotate the mig gun and change the angle in the direction of travel. In general if you have the gun at 90 degrees to the plate in the plane of travel you will get the most penetration and strength of weld. Changing the angle can change the amount of penetration as well as the appearance of your weld.
Finally, you can push or pull the gun while welding. Most instructors will teach you to pull the gun from left to right while welding and angling the gun slightly in the direct ion you are travelling. This helps ensure you get adequate fill and the shielding gas stays concentrated around the weld pool. I my self like to push from right to left as I am right handed and can see better with this method. You will get generally get a flatter weld bead and have to be careful as now the shielding gas can sometimes become interrupted and you will get porosity in your weld.
Equipment
When purchasing a welder you will generally have lighter duty machines that run .023 welding wire and have lighter duty cycles, meaning that for every minute of continuous weld you have to let it cool for so many minutes. For a large majority of hobbyists and home users this never really becomes an issue as you are never welding straight for extended periods of time, you generally tack parts and then make a couple welds and then it cools while you move onto the next piece. These small welders do really well on light gauge materials, like body panels, mufflers, etc.. they can weld up to 1/4" thick material in a single pass in some situations.
Next we have higher amp rated machines and usually come equipped with a mig gun capable of running 0.035 & .045 welding wires ( usually you just switch out drive rollers and contact tips to switch between sizes.). 0.035 wire is the most common and will serve you for 99.9% of your projects. 0.045 and in some cases 0.065 is used when you are are not wanting to make multiple passes.
You also can run your welder using flux cored wire to avoid using a shielding gas although you will get a lot more spatter that you need to clean up later. For best results you would want to S-6 welding wire and a tri-mix welding gas. A tri-mix is more money than straight CO2 and usually blends oxygen, helium, co2 and sometimes argon. You will get cleaner welds, better wetting action, better tie in and the least amount of spatter.
Tri-Mix is a heck of a lot more pricy then a common 75/25 for welding common mild steel these guys are working on,Tri-Mix is really an overkill for these situations.
If you are getting any spatter with fluxcore,you are just plain not running it right,it's a whole different animal and technique compared to hardwire..
In my shop we have a large Cannox 450 Amp 3 Phase welder. It is a power supply with stand alone wire feeder. We can run up to 0.065 wire with it but 99% of the time it is loaded with Lincoln Murex S-6 0.035 wire. We also have a Lincolm 350MP with a 25ft push-pull gun set up for welding aluminum. We have a Lincoln PowerMig 255 (Approx $2500.00 here in Canada) and a Lincoln PowerMig 216 (Around $1800). The 255 can adjusted in finer increments, has digital gauges, and is slightly higher amperage that the 216. We picked up the 216 at auction for $400 bucks so we had a spare welder around in the event one of ours goes down.
In the past I have used the Millermatic 252's and just did not like how they welded but that is my preference, they do make great equipment, I just prefer the lincoln stuff. Also I run all the same consumables in my guns so I do not have to stock different parts for each system.
Other Notes
I also read one of the posts that stated if you are butting pieces of metal up you want to bevel them at 45 degrees to weld. This is incorrect. You want to put a 30 degree bevel on the plate so when you but the two pieces together you get a 60 degree included angle for your weld. Also you do not bevel all the way to the bottom. in most cases you leave a 3/32" flat on the bottom of each piece and then gap the plates by 3/32" to get proper fill.
That would be in a test shop or strict coded work that is required by a stringent weld QC process sheet,the angle on it only depends on the thickness of the base metal being welded,i've had weld process sheets tell me me several different angles it had to be beveled,many at a 45...
The main purpose of a bevel is to ensure a total 100% penetration and fusion of the welded joint,as long as the bevel is wide enough to ensure no pockets and lack of fusion,it really doesn't matter what accurate bevel it is,you are just opening up the joint to be able to weld all the way through,you just need enough to penetrate and fuse all sides of the welded joint..
This was a long post and I tried my best to describe things as best I can. If anyone is interested I can post some diagrams if that will help.
Also feel free to ask questions. I will try my best to answer.