Understanding Cutting Wheels

First in a series of articles written exclusively for White Cap customers, this article provides a basic understanding of abrasive cutting wheels, their construction, how to choose the best wheel, and how the right combination of an adhesive and abrasive can make or break a job.

To learn more about how to choose the right abrasive wheel for any job, maintenance tips, and safety best practices, check out Abrasive Wheel Selection and Applications.
 

 

Abrasive Wheels

An abrasive wheel creates a high-quality finish on surface materials, such as steel, glass, copper, stone, even concrete, with shape and dimension. 

An Abrasive Wheel is a precision cutting tool with an abrasive surface coated with thousands of hard, sharp grains that cut, chip and grind away metal, steel, copper, cast iron, stainless steel, stone, concrete, and other tough materials. The sharp grains are bound with a special adhesive to a backing, usually in the shape of a wheel.
 
As the wheel rotates on a grinder, the wheel cuts the material, causing the sharp grains of the wheel to break off, exposing new sharp edges. When the grains wear down, they fall off the bonded backing, exposing sharper new grains in their place. As the grains grind away, the surface material is removed in small chips or thin ribbons. The process continues until the material is completely cut. 

Available in a wide variety of types, shapes, patterns, sizes, and abrasives, there are several factors to consider when choosing a abrasive wheel.
 

What Is a Cutting Wheel?

The key advantage to using a cutting wheel and angle grinder is that they are easily configured to cut when needed.

.045 cutting wheels are designed specifically for cutting metal and a reduced thickness (known as “Kerf”) than grinding wheels (1/4”) and pipeline wheels (1/8”).

This is because grinding and pipeline wheels are mainly designed for grinding metal as opposed to cutting. The added thickness of a grinding wheel makes it difficult for cutting jobs, as the user would need to remove more material in a cut, leading to a longer cutting time and frustration. 

 

Cutting Wheel Types

There are two basic configurations of cutting wheels: 

• Type 41(1): This is a flat cutting wheel that allows for a maximum depth of cut. The main disadvantage of using a Type 1 wheel is that they mount closer to the guard making it more difficult for the user to see what they are cutting. 
  
  
• Type 42(27): Originally developed and patented by United Abrasives, this design features more of a rigid feel while cutting, enhanced operator visibility of the cut, and the ability to flush cut as the raised hub allows for the locking nut to be recessed. These wheels are also available with a 5/8-11 quick change hub for ease of mounting. 
  
   

 

Grains

The grains within any abrasive are what actually do the cutting or grinding.

The grain used in a cutting wheel determines the disc’s cutting speed, life and cost ratio. You’ll find four different types of grains for cutting wheels:

• Ceramic - Ceramic grain utilizes the latest technology in abrasives. By design, it features thousands of sharp cutting edges which fracture under relatively light pressure and expose new sharp cutting edges. Ceramic cutting wheels allow for a very long life and fast cutting speeds. Ceramics also tend to cut cooler, minimizing discoloration while maximizing product life.
  
  
•  Zirconium - Zirconium grain has an extremely durable design. These wheels are used for high performance cutting with long life and feature a low cost-per-cut ratio.
  
  
• Aluminum Oxide - Aluminum Oxide is the most common abrasive grain and delivers very good cut rates and durability. It tends to have a lower initial cost for the user which lends to its popularity..
  
  
•  Silicon carbide grains are extremely hard, very sharp, fast cutting but break off easily under high pressure. Harder than aluminum oxide and versatile for grinding soft metals like aluminum, copper, or cast iron as well as hard materials such as cemented carbide, stone and concrete. 

Grit/Grain Size

Grit, or grain size, ranges from coarse to fine. and is indicated by a number shown on the abrasive wheel's label. The larger the grit number, the smaller the grain, and the finer the finish. Large/coarse grains grind larger chips resulting in a rougher finish.




 

Bond Material/Matrix

The bond (sometimes called a matrix) is the “glue” that holds the key elements to a cutting wheel - the abrasive grains. Bonds help to determine the type, the characteristics, and the performance of an abrasive wheel. The stronger the bond, the longer the grains adhere to the wheel. This means that sometimes a weaker bond is a better choice when cutting strong, tough metals that need razor-sharp abrasive grains.

Abrasive wheel bond types:

With different degrees of strength, there are six standard bonds. There is not a best-to-worse ranking or “best” bond because each offers such unique characteristics that the best bond is one that suits your current particular grinding operation.

• Vitrified: (V) Made from clays and fusible materials. Not susceptible to water, oils, acids, or temperature variations. Ideal for high stock removal and precision grinding projects.
  
  
• Resinoid: (B) Resins are mixed with abrasive grains to produce a soft, fast, and cool bond for wet or dry grinding, good cutting performance, and usually the least expensive bond. With a low curing temperature, resinoid wheels are tougher and less rigid than vitrified, making them good for all kinds of abrasives, especially heavy duty projects. However, they are affected by acid, humidity and weather extremes.
  
  
• Silicate: (S) Releases abrasive grains easily, creating mild, cool cutting actions good for projects that require minimum heat and good for sharpening edged tools.
  
  
• Shellac: (E) Made from natural and synthetic shellac, this bond has exceptional cool cutting and suited for grinding copper and other soft materials. Highly recommended for special applications that require a high-surface finish such as razor blade and roll grinding.
  
  
• Rubber: (R) Made from natural and synthetic rubber and used mostly in centerless and control abrasive wheels. Good for precision and fine surface finishes. Using wet grinding and thin cut-off wheels produce burr- and burn-free cuts.
  
  
• Metallic: Have limited use when compared to vitrified and organic bonds. Most use a diamond abrasive which removes material slowly and usually with high speed. Good for glass grinding, abrasive wheel shaping, concrete or stone sawing, and has a long-life span. Can be used with aluminum oxide or diamond abrasives to produce conductive abrasive wheels for electrolytic grinding.

 

Cutting Wheel Safety - Best Practices

• Always wear protective safety glasses or face shield with impact-resistant lenses and side guards. 
• Install shatterproof safety eye shields over all stationary grinders.
• Before mounting, check abrasive wheels for cracks, chips, and damage. Repair or replace as necessary.
• Make sure operating speed does not exceed rated maximum wheel speed.
• Inspect and ring test wheels for cracks before each use.
• Be sure the abrasive wheel hole fits the machine arbor properly.
• Check that flanges are clean, flat, and the proper type and size for the wheel you’re mounting.
• Tighten nuts just enough to hold wheel firmly. Do not use excessive pressure.
• Standing to the side, run new wheels at full operating speed in a protected area at least one minute before grinding. If a defective wheel is going to break, it’s likely to happen when it    begins to turn.
• Grind a wheel at a rated speed LESS than rated grinder speed.
• Only mount ONE wheel per single arbor.
• Use wheels and grinding machines only for the purposes they are intended.
• Be aware of excessive vibration. It’s an indicator wheel is out of round.
• Never grind towards yourself or another worker. Always try to grind towards a wall.
• Be sure the third wire is grounded to avoid shock.
• Make sure that a portable grinder has completely stopped before setting it down. Use a stand if possible. Rest grinder on its guard if there is no stand,
• ALL grinders should be used ONLY with a protective hood over the wheel.
• ALL grinders should be inspected every 30 days and necessary adjustments and repairs made.
• Don’t stand directly in front of a grinding/cutting wheel whenever a machine is in operation.
• Don’t grind or cut material for which the wheel is not designed.