Cutting metal with a gas torch is accomplished by pressing a lever on the torch that shoots a stream of pure O2 into preheated metal. This triggers a chemical reaction, causing the metal in its path to rust away as the torch flame hits the area to be cut. Of course, this only works on steel and other ferrous metals. For aluminum, titanium, copper, and other non-ferrous metals, an alternate cutting method is needed.
By all accounts, the oxy-acetylene “kit” remains the cheapest, all-purpose welding/cutting combination on the market today. Acetylene gas mixed with oxygen produces nearly 7000 degrees farenheit, enough for many different welding tasks. The high heat is likewise necessary to generate the rust reaction that facilitates cutting. Other fuels, like propane and Mapp gas, may also be used to cut ferrous metals using a gas torch.
In addition, with a special tip called a rosebud, a gas torch allows you to heat metal for forming or annealing purposes. A rosebud can also help you loosen tight bolts and nuts. It’s also possible to use the tip to preheat a weld joint prior to welding.
An oxy-acetylene kit should include a torch handle, several different size nozzles (welding tips), a cutting tip (and lever) and a rosebud tip. Unfortunately, many inexpensive kits skip some of these accessories, so pay close attention when shopping around. More importantly, the torch handle should be outfitted with flashback arrestors and check valves for safety. These items prevent flames from traveling up through the hoses, which could enable your gases to mix and ignite inside the hoses. You’ll also have to purchase a refillable gas cylinders that provide your fuel, as shown in the photo below right.
A good kit also includes high-quality regulators for both the oxygen and acetylene (or alternative fuel) tank, as well as a gas hose for each (red and green). Most kits come with tip cleaners, a flint striker and set of goggles. You’ll have to supply your own gloves and a suitable work area for welding. This typically means purchasing fire clay bricks, either from a ceramics shop or company that sells fireplace and other refractory supplies.
The diagram above illustrates the basic set-up of an oxy-acetylene cutting operation.
Plasma Cutting works on all metals, ferrous and non-ferrous, thin or thick. It’s particularly effective for gouging holes into aluminum or stainless steel, leaving behind no trace of carbon contamination. However, it’s less effective on dirty metal and aluminum plates in which aluminum oxide has built up. So be sure to clean your work pieces prior to cutting.
The process utilizes an inert gas (nitrogen, argon, or oxygen) that streams through a narrow tube inside a nozzle. An electrical arc on the plasma gun strikes the gas, ionizing it. This is what generates plasma, which physicists like to refer to as the “fourth state of matter”. The concentrated heat produced by this chemistry is sufficient to blow through hard metal like it’s a piece of paper.
Air Carbon Arc Cutting
Air carbon-arc cutting is a process of cutting, piercing, or gouging metal by heating it to a molten state and then using compressed air to blow away the molten metal. In terms of what you hold in your hand, it has a similar set-up to stick welding. There’s an electrode holder and a “stick”. Here, the stick is made of graphite and carbon. This is coated with copper to help maintain an electrical connection through the holder into the machine.
In the air carbon-arc process, a stream of compressed air is aimed at the point of contact with the base metal. There’s a valve in the holder for turning the compressed air on and off. Unlike a welding machine, this equipment includes an air compressor and hose. The size of the compressor ranges between one and ten horsepower, depending on the electrode sizes, amperage range and duty cycle at which the machine operates.
You can use this process to cut metal, gouge out defective metal or bad welds, or to bevel a groove for welding. In most cases, you’ll probably have to do some grinding and other clean-up of the metal afterward, since the cuts made are generally not as precise and pretty as plasma cutting. On the upside, the cost is far cheaper. Using compressed air also saves you the hassle and cost of refilling acetylene and oxygen tanks. In addition, since the area affected is small and the process quick, the surrounding base metal won’t reach a high enough temperature to potentially compromise its structural properties.
Air carbon arc cutting takes the form of either a manually operated venture (as shown in the photo above), or with the help of a travel carriage to help you get long, even cuts. The manual process can be used in all positions, but overhead cutting can be difficult.
You can cut aluminum, copper, cast iron, magnesium, and stainless steels. Holders are available in several sizes, depending on the duty cycle of the equipment, the welding current, and the size of the carbon electrode you’re using. For extra heavy duty work, water-cooled holders are needed.
For more info on CAC, read the overview posted at WeldGuru.com
After welding a joint, it’s a common practice to grind a weld bead down with an angle grinder. (Cover weld beads are usually kept in tact, but root-and-fill passes in pipe welding are frequently grinded.) In addition to finishing surfaces, angle grinders can also be used to create beveled edges on the fly for plate or pipe joints, or to prepare base metal surfaces prior to grinding. The tool easily removes rust and other oxides.
Nowadays, the most widely used angle grinder handles 4 1/2 inch diameter grinding discs. Larger grinders use discs up to 9 inches and are ideal for beveling thick-walled pipe. The other variable to consider when shopping for a grinder is the motor’s amperage. More amps means more power and the ability to grind faster. A 10-amp angle grinder is standard in industry, while students and hobbyists more often opt for a 6 to 7.5 amp grinder.
Angle grinders accommodate a variety of abrasive discs, which are divided into five categories:
- Grinding discs – These eliminate material, like excess weld metal, weld spatter, burrs, and the rough edges of oxy-cut material.
- Cutting discs – These work like a mini-circular saw to cut through metal.
- Flap discs – These polish and smooth metal in advance of a paint job, powder coating or bend test.
- Wire brush discs – These are used to remove weld spatter and slag from welds without altering the surface of the base or weld metal.
- Sanding discs – This requires a special spindle adapter to handle flat, rounded sheets of sandpaper.
Smaller types of grinders and deburring tools are powered by an air compressor rather than an electrical outlet. Since they don’t contain a motor or battery, these tools are designed to fit in tight spaces, like corners and interiors.
You’ll also find a stationary (aka bench) grinder set up in most shops. This equipment is used to sharpen tools, smooth out bevels cut in metal stock, or for quick rust-removal of small plates before welding. Home improvement stores generally sell affordable models for consumers, so be sure to consider one if you’re setting up a shop.
A tungsten grinder (left) and a bench grinder.
For TIG welding, a special tungsten grinder is also a necessity. Both portable and stationary models are available to grind this exceptionally hard metal down to a sharp point. (And both are expensive.) During welding, the tungsten tip will occasionally come in contact with the molten puddle, losing its point. That’s why the grinder must always be closeby. In the field, the portable version is plugged into an outlet on the welder- generator. See the Welding Guides and Videos page for a video on this subject.
Next: Other Shop Tools