One of the finer points of engineering machinery is to build it so parts that will need to be replaced down the line are accessible. All too often, metal must be cut to remove and replace failed parts.
As often as not, someone other than the manufacturer will have added something that is permanently attached, which interferes with easy disassembly.
The old standby is the oxyacetylene torch. It works to cut ferrous metal, iron or steel. Note that true stainless steel is a whole different breed of cat and, depending on its makeup, may not cut readily with the torch.
A hot flame of pure oxygen and acetylene will rapidly raise the temperature of the surface of iron or steel to the melting point. This is observed by seeing a glowing orange spot of liquid metal.
At this point, the operator will open the cutting valve and send a stream of pure oxygen into the molten metal. This causes high-speed oxidation, which the jet of oxygen pushes through the piece of metal. Molten oxidized metal flows from the work area and leaves an opening in what used to be a solid piece of steel.
How clean and straight the cut is has much to do with the skill of the torch operator, the condition of the tip of the torch and the cleanliness of the metal workpiece.
The orifices on the tip of the torch must be kept free of debris so the gas or oxygen that comes out under pressure flows freely and in an aimed pattern. Cutting material that is not clean or that does not cut clean (like heavily rusted or multi-layered pieces) will add to fouling the tip. Using it as a hammer while cutting is also prone to foul the tip.
When the workpiece cannot be made “like new” – clean and shiny – there is one trick to make cutting easier. Once you have begun the cut, tip the torch so that instead of the jet from the torch tip being at a 90-degree angle to the workpiece, it will be closer to 45 degrees and undercutting the work area.
The jet of oxygen that is making the cut happen will be working on pure metal below the surface crud and will not have to penetrate the surface crud to make the cut happen.
Note that the acetylene is only necessary to heat the metal to the point that the oxygen jet will cause the high-speed oxidation. Most operators lack a steady enough hand to demonstrate this by turning off the acetylene while making a cut.
A variation of the oxyacetylene torch is the oxypropane torch. The big advantage is: Propane is less expensive than acetylene. The trade-off is: Acetylene burns significantly hotter than propane. A regulator specific to propane must be used; the regulator for acetylene cannot be used for propane.
Either will cut iron and steel of varying thicknesses, the limit being the patience of the operator and the size of the cutting tip on the torch. Thin materials are a challenge, and metal warpage is a factor.
The plasma cutter works wonders within its design parameters. Sometimes called a plasma torch, this device uses electricity to create the heat necessary to melt the metal surface.
A jet of compressed atmospheric air in conjunction with the high-voltage electric arc makes a fast, relatively clean cut. The plasma cutter works with any metal that will conduct electricity.
Less heat is generated making a cut with a plasma cutter so thin materials can be cut without warping the material. The jet of compressed air that is part of the cutting process seems to also cool the workpiece.
Other than replacement tip pieces, called consumables, electricity and compressed air are all that is needed to make the plasma cutter work. Though it uses a visible electric arc, ordinary dark-lensed cutting glasses will shield your eyes from damage from the bright arc light.
Plasma cutters are available starting at less than $300. Don’t plan on employees getting good service out of the cheapest unit you can find. Some entry-level units will work with normal house current 110-volt power, while the larger units will need 220 or 440 volts.
The most inexpensive units work best on very thin materials. The cleanliness of the cutting surface is critical to the lighter-duty plasma cutters. Paint, oxidation and ordinary grime all interfere with the conductivity of the electrical arc. A ground cable, similar to that used with an arc welder or other type of electric welder, is used with a plasma cutter.
Compare advertised cutting thickness ability and duty cycle, and make sure consumables are readily available when purchasing this product. Buy a heavier unit than you foresee needing, and you’ll be happier.
A good old chop saw will pay for itself in just a short while if your shop builds things using small pieces of metal welded together. A piece of steel cut to size on a chop saw is ready to be welded in place, while a piece cut with a torch will need cleaning up with a hand grinder unless both the torch operator and welder are world-class.
Most chop saws (also known as cutoff saws) allow you to clamp the workpiece in place at angles other than 90 degrees. They also blast sparks all over the place, so make sure that what is in the area is not flammable or easily damaged by abrasion. And for the love of Pete, wear eye protection.
Anybody can burn up anything electric, but a mid- to high-end unit from a name-brand manufacturer will last longer than the cheapest cutoff saw you can buy.
An angle grinder is one of the most versatile cutting tools. A standard grinding disc works well for smoothing metal, and a cutting disc – sometimes called a “skinny wheel” – works well for various trimming. Four-inch to 7-inch disc size is the normal range.
The 7-inchers are usually 15 amps, and the smaller units may be anything. My favorite is a 5-inch unit that is 12 amps. It’s less than half the weight of a 7-inch unit and almost as powerful.
Note that angle grinders cause more fires than cutting torches. That, in my less than humble opinion, is because most people know something that throws fire can start other things on fire. The sparks from an angle grinder are hot enough to start fires, so please take note of where your spark trail lands.
A cutoff wheel on an air die grinder is small enough to get into places a regular angle grinder can’t reach. These little guys turn at up to 20,000 rpm and, for their size, they cut, trim and smooth very well.
A rotary file used on an air die grinder is also very useful. Especially when a hole is almost big enough.
Safety alert: While the sparks and debris thrown from grinders can injure eyes and bare skin, the particles thrown from a rotary file are razor-sharp shards of steel that will do serious damage to your eyes. Used on non-ferrous metals, the rotary file will load up with material rather than expelling it.
- Second safety alert: Metals other than iron and steel are prone to partially melt and stick to the grinder disc or wheel. If the operator keeps the pressure up, enough heat can be generated to cause the grinder wheel to disintegrate.
If there is space and you don’t want to make sparks, the good old hacksaw or a reciprocating saw may be the answer. Reciprocating saw blades are amazingly strong and sharp. They are available in various lengths and are capable of cutting metal, wood or plastic – or the demolition blade, which is capable of cutting through wood and nails.
- Third safety alert: Prescription eyeglasses are not safety glasses. There are safety side shields that can make ordinary glasses into passable safety glasses, but things like the rotary file really need a full-face shield in addition.
Remember that no matter what you need to cut or what you cut it with, it will be better if you don’t get blood on your project.
Brad Nelson has been a dairyman, a hay hauler, an export hay company plant manager, a hay buyer and is addicted to fixing things – and telling tales.
PHOTO: 1.The angle grinder shows two types of discs, a flapper-style smoothing disc (installed) and a grinding disc (lying on the workbench).
PHOTO 2. The reciprocating saw has blades suitable for metal (shorter one) and wood, including wood with a stray nail (longer one).
PHOTO 3. Chop saws can be useful when an angled cut other than 90 degrees is required.
PHOTO 4. This grinder wheel shows aluminum starting to coat the wheel. To keep grinding non-ferrous metals when this happens can generate heat adequate to disintegrate the wheel.
PHOTO 5. This is the tip of a plasma cutter. An electric arc creates the heat, and compressed atmospheric air blasts out through the center orifice to melt through the metal being cut. This will work on any metal that will conduct electricity.
PHOTO 6. This cutoff wheel is used in an air die grinder (at 20,000 rpm).
PHOTO 7. Although prescription glasses with side shields installed offer a measure of eye protection, regular safety glasses are recommended to prevent glass shards from entering the eyes, and full-face shields are recommended when using a rotary file.