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[steel] Simple Cutting

Much of what we do with steel in machining is considered "cutting steel". This topic deals with simple, basic cutting methods.

There are two or three basic methods of cutting steel. The most popular either use mechanical means or heat to cut basic shapes.

When I speak of basic shapes, I mean to cut such things as steel bars into specific lengths, or to cut such things as plate metal into various widths and/or lengths.

Mechanical
Basic mechanical means of cutting steel include hacksaws, bandsaws, and abrasive saws. Probably the most simple and most often used method is a variation on a bandsaw. A bandsaw is simply a motor driving a metal blade that is in the form of a long band. The long blade is welded back upon itself. This type of cutting is normally used to cut lengths of bars, tubes, rods, and other discrete items.

Another simple mechanical cutting tool is an abrasive saw. This machine is very similar to a common circular saw used in home carpentry. However, it is normally much larger, and is usually mounted onto a table. The blade of this saw is made of a strong, but flexible substrate (fiberglass or another composite material) with abrasive substances impregnated in it. As it is used, the edge of the blade wears away over time, rather than getting dull like a metal blade does.

Heat
Probably the most recognizable heat-based method of cutting steel is the acetylene torch. This torch mixes acetylene gas (which is highly inflammable) with a controlled mixture of oxygen. By carefully controlling the mixture, the operator of this torch can produce an extremely hot, tightly focused flame. The torch can be used to cut curves, straight lines, and essentially any possible two-dimensional shape. It can even be set up with computer controls to cut very exotic 2D shapes.

Another common heat-base method is a plasma torch. In this case, a complex torch head is used to strike a very hot spark. The electrical components of the torch keep the hot spark continually forming. Meanwhile a gas is pushed through the spark, where it changes form into a plasma. Gasses that are commonly used in this method include argon, CO2, oxygen, and even simple compressed air. Each gas has particular properties that are important to know in how they assist or hinder the cutting process.

Laser cutting has become quite popular. Its very tight focus and incredible heat can make cutting of tightly detailed shapes very easy. As far as I know, laser cutting is always done with computer controls. It is also only useful for cutting very thin plate steel. Normally its cutting depth does not exceed about 1/16 of an inch (about 1.6mm).

Cutting Simple steel

There was a time when I loved to arc weld using a high voltage electric arc welding machine. Most of the time I worked with thick pipe and hardened metals that would be difficult to go through with a hack saw or bolt cutter (I did not have a jig), so I raised the watts on the arc, picked up a large rod (about 5mm) and then used pure heat to burn the metal and it acted as a method for cutting. It was quite effective save for the rugged outline it left as the metal dropped like water.

Offtopic but, If you have never seen this process simply ask a welder to borrow his dark lens mask and look as he strikes the rod against the metal - it is marvelous to see what immense heat can do.

[steel] Simple Cutting UFO & Writing Art Education Sciences

The only problem with cutting that way, using an arc welder (stick welder), is that it is impossible to make an accurate cut. The intense heat causes the cut surface to pit and melt unevenly.

However, it certainly is fun to do.

Offtopic but, I worked as a welder, using MIG machines, for a couple of years just after high school. Still one of the most enjoyable jobs I have ever had.

Cutting Simple steel

I did some of my engineering schooling on another type of steel abrasive cutting. It is called, water jet cutting. Believe it or not, if you get water flowing fast enough it can actually cut metal (speed up to and beyond Mach 3 on certain tools).

The basic principle involves a narrow, focused, water stream mixed with abrasive particles (special sands). It is sprayed with very high pressures resulting in high velocities. Because the water is flowing so fast, it can cut through many materials. The water jet reduces cutting forces, and virtually eliminates heating. Unlike metal cutters, a water jet never gets dull and it cannot overheat. The basic cutting mechanism is erosions.

There are of course advantages and disadvantages to all types of machining and cutting. Some of the advantages to water jet cutting include the following.

- You can cut virtually any material
- You can achieve smooth finishes without gasses or oils
- Setup/fixturing involves placing the material on the table
- Thick materials can be cut (to tolerance up to 2" thick and 5" or thicker where tolerance is not important)
- You have no heat affected zone
- No mechanical stresses
- Material yield is maximized

On the flip side, there are some disadvantages to water jet cutting. Although it is possible to cut tool steel and other hard materials, the rate of cutting has to be reduced significantly and the time to cut can be extremely long. Another disadvantage is dimensional accuracy on very thick parts.

All things considered, I have found that water jet cutting is a highly favorable method for cutting steals. It was always one of my favorite methods to use.