Cutting Torch Overview
Cutting torches or oxy-fuel cutters, as they’re technically called, are tools that many different professionals use daily. For the welder, they’re also useful for trimming material or making cuts before welding.
The torch excels at tasks where extreme precision isn’t required but speed is. Take for example removing a car’s old muffler or exhaust system. Sure you could fire up your plasma cutter (and compressor) or break out the sawzall, but why bother- especially if what you’re cutting is going into the garbage. Cut, drop and done.
If you’re just getting into welding as a hobby, you may not have thought a torch outfit is necessary equipment to have in your workshop. Its versatility and ease of use may change your mind however.
Let’s take a closer look at the Oxy-Acetylene cutting torch and why every shop should have one in their inventory.
How Does a Cutting Torch Work?
A cutting torch consists of three main parts, the torch gun, a fuel source and an oxygen source. The two gases are typically supplied from standard cylinders and are connected by hoses that feed them to the nozzle on the torch itself. Incoming fuel and oxygen is regulated at the cylinders and controlled at the torch handle via valves for adjustment. Setup is not complicated but can sometimes can be tricky to get just right.
The fuel gas, which is usually acetylene or a similar gas, mixes with the oxygen and is ignited to create an initial flame. The cutting process is a chemical reaction between the oxygen and material to be cut (usually steel) which forms a molten iron oxide.
Once the material to be cut is pre-heated to a cherry-red appearance, additional oxygen is injected via the torch blast trigger at high pressure. This has the effect of producing more heat and thus creating the iron oxide which is then blasted out of the cut.
The process is self-sustaining. While the torch is initially used to start the process, additional heat is produced by the melting metal allowing the cutting to progress.
The flow rate of the oxygen is the key to the type of cutting. The more oxygen that mixes with the fuel, the wider the cut will be. Reducing the oxygen creates a narrower more precise cut. Too little oxygen however, will reduce cutting ability and increase the time needed to make the cut.
Different torch tips (with different flow rates) can also be used to cut through thicker materials.
Fuel Options
There are four main types of fuel used with cutting torches. Selection is based on cutting needs, availability and sometimes budget.
Acetylene
Acetylene is the most common because it burns the hottest. This allows you to make very clean cuts with it, and its high heat allows it to be used to cut a variety of metals.
Being highly flammable and spontaneously combustible in air at pressures above 15 psi, acetylene requires a bit more precaution than other fuels. Cylinders are shock sensitive and must be handled with care.
Acetylene can also be more costly than other options.
Propane
Propane is another option. It takes a little longer to heat up than acetylene, but it burns fairly hot and is a good alternative. It’s also cheaper. Distance to the material to be cut must be adjusted however. Propane’s flame characteristics place the ‘sweet spot’ further out compared to acetylene. With acetylene, the hottest part of the flame is the center of the cone. With propane, it’s actually the outer part of the cone.
HGX propane
HGX propane is a newer fuel option. It’s a mixture of HGX-3 and regular propane, but it burns about 15% hotter than standard propane does. At its hottest, it reaches the same temperatures as acetylene. The mixture doesn’t require much HGX-3. The ratio is one gallon to 1,000 gallons of propane. Unlike acetylene, which needs to be carefully stored, propane and propane mixtures have more flexible storage options.
Propylene
Propylene is another option for your cutting torch fuel. It’s similar to standard propane in that the outer part of the heat cone is the hottest. Propylene burns cleaner and has a lower consumable cost due to the increased tip distance when cutting. This fuel is considered more stable and safer to store compared to acetylene.
MAPP
MAPP gas was originally a trademarked brand of gas that contains a mixture of propadiene and methylacetylene. Today the name has become synonymous with a number of similar gas mixtures, and true MAPP gas is no longer produced in the U.S. Most fuels classified as MAPP gases today are mostly propylene with a very small amount of additional gas added.
While probably a better fit for Oxy-Fuel welding, MAPP gas can still be used for cutting. Like other alternative fuels, you will require a different nozzle and additional pre-heat time as MAPP gas burns hotter than Propane but not as hot as Acetylene.
Its also relatively safe to store and is available in many hardware stores as a small self-contained kit which can be handy for quick projects or emergencies.
Changing Fuels
Changing fuels is possible but requires different tips and possibly hoses. The tip of each cutting torch is specially designed for one type of fuel. Using the wrong tip makes it difficult for the fuel to reach its highest temperature and will impact how effective it is. Always consult the safety information for the fuel you’re currently using before switching components or using the cutting torch.
When purchasing a new tip for your torch, you will want to look at whether the tip is a one-piece tip or a two-piece tip. One-piece options were originally designed for acetylene and are made out of copper. They have either four or six holes in them to pre-heat the fuel. Today, you can find one-piece tips for acetylene, propylene, and MAPP gas, but you will want to make certain the tip has the correct number of pre-heat holes for the type of fuel you’re using.
Two-piece tips are used with propane and other slow burning fuel. Again, you’ll want to make certain the tip you’re using is designed to work with your fuel and with your cutting torch.
Different fuels also require different amounts of oxygen to achieve their highest flame temperature. So for example when using acetylene, its maximum flame temperature in oxygen is achieved with a 1.2:1 fuel to oxygen ratio. Propane on the other hand requires a ratio of 4.3:1.
Pros and Cons of Using a Cutting Torch
There are other ways of cutting metal, including using a reciprocating saw or a plasma cutter. So what makes a cutting torch a better option? It does have several benefits.
PROS
- For those who need to take their equipment to other locations to work, a cutting torch offers a bit more portability than other methods especially if access to electrical power is an issue. Smaller tanks are also available which when used with a wheeled cart, makes moving a cutting torch setup pretty painless.
- Compared to a plasma cutter, what the cutting torch gives up in precision, it more than makes up with its ability to cut far thicker materials. A heavy duty plasma cutter might handle material between 2″ and 3″ thick. The oxyfuel cutting torch will easily cut through plate thats 6″ thick or greater.
- It’s also relatively inexpensive. While over time, gas costs can accumulate, the up front costs of a good torch outfit are well below that of a plasma cutter and even competitive with name brand reciprocating saws.
CONS
So what are the downsides?
- As mentioned above, you’re certainly not going to get a ‘laser-like’ cut as you would with a plasma cutter. An experienced oxy-fuel operator can come close though. There’s also many more types of cuts available with a plasma cutter where a torch is limited depending on the type of nozzle used.
- Probably the biggest disadvantage compared to other methods is the kind of materials that can be cut. Need to cut stainless steel or aluminum? Not happening with a cutting torch. A plasma cutter will cut steel, stainless steel, aluminum, copper, brass and more as long as the material to be cut is electrically conductive.
- And finally, there’s also the cost of the fuel. Acetylene is a manufactured gas and the price does fluctuate. Plasma cutters will go through some consumables (electrodes and nozzles) but use compressed air as a fuel source.
Final Thoughts
If you’re new to welding and metal cutting, the Oxy-Acetylene cutting torch is a great option that won’t impact your budget too much. Whether cutting off thick plate or just loosening up a rusted bolt, a cutting torch setup can be beneficial to every home workshop or garage.
