Three Ways to Hot Cut Your Metal

cutting torch in action
Cutting metal, the hot way. photo courtesy United States Navy

If you have some metal that needs to be trimmed or cut to shape, you're already wondering what the best way to cut metal is. Do you need to fix a dent? There are three main ways to cut metal using heat. But before I get into that I want to address the term "heat" for those of you who may not be familiar. When you're talking about metalworking, there are almost always two ways of walking into a task -- cold or hot.

Let me give you an example. If you want to join two pieces of steel together, one way to do it is to create a cold joint. A cold joint is simply a joint that used no heat to create it. Examples of this are screws and bolts. Two sheets of steel joined in a cold lap joint will be overlapped by a certain, uniform amount then receive a series of nuts and bolts holding them together. No heat was involved, and a solid joint was still created. The same two pieces of steel can be combined using a hot joint. A hot joint simply means that heat was used to create the joint. Using a similar example, two pieces of steel are overlapped a uniform amount, and a mig welder is used to weld the two pieces of steel together. You have a nice, strong joint that used lots of heat to combine the pieces. A hot joint. The same can be said for cutting metal. Most people are familiar with a cold cut. A cold cut is a cut that doesn't use any kind of heat to make the cut.

A very simple and easy to relate to example of a cold cut would be a cut using a common hacksaw. A hacksaw uses the teeth of the saw to remove material a little bit at a time, but no heat is applied. To be fair, there is some heat generated with cold cutting, and it does help make the cuts, but the principal does not require any heat to work.

Hot cutting involves adding heat, and there are three examples I can give you with varying results.

Friction Cutting

Most people are familiar with some form of friction cutting. A friction cut involves an abrasive disk made up of some mixture of stone and other hard material. The cutting wheel on a Dremel is a friction cutting disk, as is the cutting wheel on a 4-1/2 inch grinder. These may seem to be cold cutting methods, but in fact the cutting wheel relies on the massive amount of heat created by the friction of the material as it contacts the metal. The metal is melted away, which is why a cutting wheel will still leave slag and throw bits of hot, molten metal all over the place.

Torch Cutting

The most common method of professional hot cutting is the torch. Specifically, the oxy-acetylene torch. This type of cutter uses a mixture of oxygen and acetylene which is mixed in a cutting tip, then ignited. It's very hot, hot enough in fact to cut right through metal! A cutting torch like this can cut through many thicknesses of metal quickly. It can be used over and over as long as the gas holds up. The cuts, however, leave a bit to be desired. It's more of a quick and dirty cutter. If you are using a torch to cut metal for a project that must be nicely finished, there will be a fair amount of clean up as the cuts themselves are fairly ragged and there is always plenty of slag the needs to be knocked or ground off before any level of finish can be achieved.

One interesting note about oxy-acetylene cutting: Once a cut is started, you can turn off the acetylene tank, let the flame die out, and continue the cut using only the oxygen. This flameless cut is made possible by the amount of heat the is held in the metal and the velocity of the oxygen ions and they are super heated and travel past the metal. It cuts. A true chain reaction.

Plasma Cutting

The plasma cutter is the cutting tool with the most finesse. This cutter uses an arc of electricity to super heat the metal and cut it away. The tool itself can be very precise, and the cutting area is quite small with very little material lost. A good operator can use the plasma cutter almost like a "cutting pen" and draw his way through the metal, creating almost any shape imaginable. The plasma cutter works extremely well in cutting sections of sheet metal.

Like most jobs, there are numerous ways to tackle any task in metalworking. the trick is getting good enough to know which one is best for the job at hand.