how do you know how big machine you need?

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How do you know how big welder you need? I'm not quite clear on the "material thickness" part, if it says a welder is capable of welding 1/4 inch material, does that mean 1/4 inch material is the maximum for safety reason or does that mean the machine is capable of penetrating 1/4 inch deep?Thanks for clearing things up.
Reply:Buy based on AMP ratings, not what the manufacture says you can weld. Technically almost any metal can be welded if its V'd out enough and you throw enough hot passes on it. But I wouldn't suggest using something that isnt up to the job. You have to first ask what materials you will weld mainly (aluminum or steel) and then ask whats the thickest piece you might weld (castings not necessarily included).Then make your decision. What process are you looking to get into?
Reply:I would look at what you think you might want to weld, then look at the next larger machine!  It's been mentioned many times here that you can't use AMPS you didn't buy!GlenMiller Dynasty 200DX - Millermatic 350P - Hypertherm Powermax 45Want to sell!! - Hobart Handler 150
Reply:Originally Posted by HelloStrangerHow do you know how big welder you need? I'm not quite clear on the "material thickness" part, if it says a welder is capable of welding 1/4 inch material, does that mean 1/4 inch material is the maximum for safety reason or does that mean the machine is capable of penetrating 1/4 inch deep?Thanks for clearing things up.
Reply:For starters, go with a 240v (aka: "220/230v") machine.Lincoln Power Mig 216Lincoln AC/DC-225/125Miller  625 X-Treme PlasmaMiller 211 Forney 95FI-A 301HF 91110Victor Journeyman O/PMilwaukee DaytonMakita  Baileigh NRA Life Member
Reply:Originally Posted by SuperArcFor starters, go with a 240v (aka: "220/230v") machine.
Reply:Knowing what you want to weld is the 1st thing. I'll leave small 110v powered machines out of the mix for right now as typically they simply don't have enough input power to do material that's very thick.A generic good rule of thumb with tig, is 1 amp per .001" of material with steel, and 20-25% more power for doing alum. (This rule starts to break down after about 250 amps roughly) So if you want to weld 1/8" steel, you'd be at roughly 125 amps and at a minimum of 150 to do 1/8" alum. Then we get into duty cycle, especially with higher amp things like alum. You can weld 1/8" alum with say a Diversion 165, but duty cycle is only something like 10 or 20%, so it's fine for the occasional hobbyist who can sit and wait for the machine to cool, but wouldn't be at all suitable for a production environment. Even my Syncrowave 200 wouldn't be the best choice if someone was going to weld 1/8" alum all day long nonstop. You'd want the extra duty cycle of say the Syncrowave 250, even if you don't need the extra amps. I think the duty cycle on the Synco 250 is like 60% at 250 amps, so at 150-180 amps duty cycle is probably almost 100%.Same applies to mig. You can mig 1/8" steel with a small 110v mig, but duty cycle is measured in seconds when maxed out to do this. My MM185 ( older 200 amp class cabinet style mig) will probably run 1/8" steel at about 60 or 70% duty cycle as compared to say a MM 211 that has the same top end output roughly, but 1/3 to  1/2 the duty cycle. A bigger mig, say a MM252 would run 1/8" nonstop all day long.Rough numbers on max thickness with mig is that you get good welds on 1/4" with a "180 amp" class mig, 3/8" on a "200 amp" class mig and 1/2" or better on a "250 amp" class mig. The idea breaks down at the upper power levels. While in theory it's possible to weld almost any thickness with multiple passes and special techniques like preheat and beveling, in reality there is a minimum amount of power that's required to get good fusion on material. Usually once you get into the mid range or higher 230v or better powered migs, you can weld whatever you need to. That usually means at least a 200 amp class cabinet style mig with a decent duty cycle. While small "homeowner" sized migs may have similar output at the upper end, the lack the duty cycle to put out that power consistently over a reasonable length of time.Stick, you can pretty much weld just about any thickness you need to if your machine will do at least 150 amps DC. More amps allows you to run larger rods and deposit material faster, but I know people who run 1/8" 7018 to do 1" steel according to the manufacturers specs.On average very few people need to weld material thicker than 1/4" regularly, maybe as much as 1/2" to 5/8" if using stick. Anyone welding thicker than that regularly is going to be up in an industrial class machine with the power and duty cycle  to easily handle that kind of material. The need for a bigger machine is usually determined by duty cycle more than max output..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:My understanding is that the manufacturer's recommendation, for material thickness a given MIG/Fluxcore CV machine is capable of welding, is:The maximum material thickness that can be joined in a single pass fillet or butt joint in the flat position; under ideal conditions.  Ideal conditions means:1 - good input power to the machine.  if it's a 120V MIG welder, then it's plugged into a 20amp rated circuit with no other equipment.  No low voltage or high voltage line conditions.  No sag in voltage during welding.  Solid, consistent input power.2 - clean bright steel at the weld joint.  No welding through rust, paint, or mill scale.  No grease or oil in the joint.3 - Whatever the recommended shielding gas mix is on the settings chart for the machine.  Usually 75/25 argon/CO2.These machines can weld material thicker than the rated max provided by the manufacturer.  HOWEVER, doing so requires more extensive preparation; using multiple weld passes, beveling material to achieve full penetration through to the back side of the weld, beveling/welding from both sides of the joint, pre-heating the material and keeping it hot throughout welding(if large pieces), and the welder must exercise tighter control over their welding technique to ensure good penetration.All that said, there are limits to what's possible with small "hobby" welding MIG machines, with small diameter wire.  The size of the welding filler metal wire limits how much current or energy can be delivered to the weld.  Large, thick sections of steel act like a heat sink and pull heat away from the weld zone.  The welding machine has to deliver a certain amount of energy to the weld in order to metal the wire and the base metal under the weld pool.  Otherwise the melted wire just piles ontop of the steel being welded, without actually joining with the underlying base material and forming a weld.  There's a reason that they don't weld tanks and aircraft carriers together using 120V MIG machines you can buy at Lowes or Harbor Freight.As someone else already mentioned, you won't see max thickness values on Stick or TIG CC power supplies.  Only on CV or multiprocess machines that use solid wire or flux cored wire filler metals.  CC processes(Stick/TIG) are generally capable of joining material of any thickness.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:And everyone is assuming that you want a stationary shop machine as apposed to an engine drive, and will we be arc gouging also? What are your future welding plans, or are you willing to purchase different machines as your needs change?