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Periodically there is a great deal of discussion on woodworking forums about the various welding techniques and types of equipment suitable for low volume use (this isn't a tutorial for professional welders). The subject comes up so regularly that I consolidated the best discussion I have found (so far) in this web page. However, I am not a welder, so if you find errors or can suggest better ways to explain something, please let me know.
Practically everyone recommends taking a welding course to learn the basics, get expert advice, have a coach to improve or correct your technique, and to help you decide what type of equipment you want. I learned a lot of woodworking by myself but got a LOT better sharpening woodworking tools with expert help and advice, so I expect welding would equally profit from a teacher or coach. Without time or patience for a course, it may pay to hire an experienced welder to fix or build your project, especially if strength and safety are involved.
Welding is melting the edges of work pieces (often steel) and adding a similar filler material to form a pool of molten material that cools to form a strong joint. This is different than soldering and brazing where the pool is a different material with a lower melting point that "glues" the parts together without melting any part of the work pieces.
The catch is that the puddle of molten metal would really like to oxidize (rust) and weaken, so much of welding art is how to protect the puddle during the process. This may be with a flux on the inside or outside of the welding rod, that melts in the heat to protect the puddle, or an inert gas such as Argon or an Argon mix.
The heat required for welding may come from an electric arc, gas flame, or other high tech sources, mostly limited to industrial use. The voltage determines the length (depth) of the arc, and the current largely determines the amount of heat (the size of the bead and how fast you can move) - you will often be dealing with 100 amps current or more. In any case, welding is a dangerous business because of molten metal (burns), electric shock, vision damage from the bright arc, poisonous fumes, and other evils. The heat and sparks are not compatible with woodworking shops - my brother was both a woodworker and an expert welder - he was terrified of a spark smouldering in some sawdust, and finding his shop on fire 8 hours later (he gave up welding when he didn't have room for separate shops).
My friend (and excellent woodworker), Stuart Ablett of Tokyo, created this summary of the basic different types of welding equipment.
Stick welding: You can, with the right rods and an AC/DC machine weld a LOT of different metals, but it takes real skill and know how, plus you have to keep those rods in good shape, which usually means a rod oven that is at a constanat temp 24/7, not exactly for the home hobbyist. (One person suggested an old refrigerator with a permanently on light bulb for heat.) That is why most stick welding done by hobbyists or farmers is on metal, using basic rods like the 6010 (DC only) or 6011 (DC or AC) which work well on most anything, have good penetration and (because of the deep penetration) don't mind a dirty surface. The 6013 and 7018 are good too, but with less penetration, they work better with thin materials. You can make much nicer looking welds, but with less penetration they need a cleaner surface preparation.
Stick welding can weld through paint and rust and deal with wind outside. Really it is not hard to learn stick welding, but to become very good at it takes a steady hand and a lot of practice. Upsides are that you can weld thicker material with a fairly basic unit, 220 Volt for sure but most homeowners have that on hand, even if you have to wire in a new 220 volt outlet. Also a good basic unit can be bought, used, for very little money. Older units might be a bit on the heavy side, but they are usually well made and will run for many more years.
The down side of stick welding: they are messy to run. Slag is the melted covering on the welding rod that created a gas cover for the welding puddle and a layer of protection for the hot metal as it cools. The slag has to be chipped off the weld when you are done. You may also need to grind off the metal that spatters out of the puddle.
MIG with flux core wire and no gas bottle, in many ways this is like stick welding with a stick that feeds from a spool so it never gets shorter as you use it. The flux is inside the wire rather than a coating on the outside of the rod.
A basic 110 volt unit (any household outlet) can weld thin materials, such as restoring a car body. However for automotive use you probably should use a GMAW unit since it is cleaner with no slag to get rid of. It may be enough for a hobbyist to learn to weld, but is not likely to be satisfactory for many projects.
A 220 volt unit can weld thicker steel, so is far more useful - Stuart considers the cheap 110 volt units a waste of money since you run into limitations too often. There are dual voltage 110 and 220 volt units, so you can weld using 110 volts at almost any regular outlet, all be it not the thicker materials, and switch to a 220 volt source when you have serious work to do.
Most FCAW (MIG with flux core) DC welding is with the electrode negative.
MIG with solid wire (no flux) and a gas bottle. With a 220V unit and the right wire you can weld from very thin steel from 24 gauge to 5/16" on a single pass. Machines like the Hobart Handler 190 are great, they also can weld stainless, with a different gas bottle and wire, and Aluminum, also a different gas bottle, wire and a spool gun, but there many package deals that the spool gun comes with. With gas rather than flux, you eliminate the slag and reduce the splatter. However, even a slight breeze may disturb the gas flow that protects the puddle, making this an indoor tool, not easily used outdoors.
Most GMAW (MIG with gas and no flux) DC welding is with the electrode positive.
By shutting off the gas, and probably changing the polarity of the welder (5 minute job to move the connections if your welder doesn't have a polarity switch), and switching from solid wire to a spool of Flux Core wire, you can also FCAW with this welder, which means you can weld outdoors.
Some of these machines are also dual voltage so you can set it up to run on 110V as well, which means you can still weld even if you don't have access to 220V power, say at a friend's house or something. Stuart suggests "If I had to had to suggest one machine for someone beginning to weld I'd say a 220V GMAW (MIG) welder with the gas bottle. You can do a LOT with one of these welders, and if you want to sell it at some point you will get good money for it, because it is a very capable machine.
TIG Welding. The arc for a TIG machine is from a Tungsten rod, which does not melt and contribute to the puddle, so a separate external rod is used for the fill metal in the puddle. Some say it is like gas welding, without the fumes! Dependent on your machine you can weld anything from razor blades to fairly thick steel. The TIG welder does take the most time to learn and it is certainly a steep learning curve, but with an AC/DC machine you can weld just about any metal that conducts electricity: steel, stainless steel, aluminum, titanium, brass, copper, bronze, cast iron and I'm sure there are some I've not mentioned.
The good TIG machines are not cheap, but they are worth it, the arc is very stable and easier to use. Good points: clean, quiet, not such heavy fumes. Bad points: steep learning curve, slow, expensive.
If I could only own one welder it would be a TIG, as most TIG welding machines can also be set up to run SMAW or Stick welding too. That being said, the TIG is slow. If I have a bunch of basic easy welds to do, the MIG, GMAW will be my go-to machine. (I happen to know that Stuart has both MIG and TIG welders.)
Most of the web videos and discussion involve DC welding, but many machines seem to have AC welding, and some of the welding rods are for AC or DC. Can someone help a non-welder like me understand when one would or would not use AC welding.
I welcome your suggestions or corrections on this or other topics on this web site.
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