The Art of Grinding Wheels
Grinders are amazing tools—but only when you optimize their use with the right grinding wheels for the task.
Learn the essentials for choosing the right grinding wheel for the job with the following primer on picking the right grain, grit, bond, shape and size. And remember, your partners at Imperial Supplies are here to help with the products and expert advice to help you have a Zen experience no matter what you grind.
Why It’s Important to Choose the Right Grinding Wheel
Choosing the right grinding wheel can be a confusing exercise. There’s no one product you can use for every purpose.
The right choice is going to depend on the metal or other material you’re grinding and the job to be done. But, that’s only the beginning. Other considerations include cost, quality and speed (as in how aggressively you want to grind). Make the wrong decision and you could ruin the metal part you’re working on, rack up your costs by burning through supplies, waste shop time or—in the worst case—create a safety hazard that leads to an accident.
The choice of grinding wheels out there is extensive, and the category offers an even more dizzying array of directions when you consider two products that are closely related to grinding wheels. Cut-Off and Chop Wheels are thinner grinding wheels you can use to cut metals. And sanding discs which are constructed of an abrasive that’s affixed to a backing like cloth or paper and usually used for finishing metal.
What Are the Key Considerations in Choosing a Grinding Wheel?
There’s a reason right angle grinders are so common in fleet shops: they’re incredibly useful in the amount of metalwork they can perform from grinding, cutting and deburring to blending, beveling and removing welds.
The tool is useless without the right grinding wheel, though. Their power and versatility depend on choosing the right combination of abrasive material, grit, bond and wheel shape for the job. Those are the main considerations this article will go into in the following sections.
Grinding Wheel Abrasives: Match the Grain to the Metal
There are several common abrasives, also known as grains, used in grinding wheels. Abrasives do the cutting on a grinding wheel. The different types of abrasives available have unique properties which make them more effective for grinding different materials. These are the most common ones, although combinations create lots of additional variations.
1. Aluminum Oxide
The most common grain used in grinding wheels cuts through steel and iron as well as softer metals like brass. Hard and durable, aluminum oxide’s versatility and low cost makes it the standard pick for many jobs in the shop. Nevertheless, it has some drawbacks which include a tendency to dull through use and not be as long-lasting as other abrasives.
2. Zirconia Alumina
The choice for rough grinding projects when a lot of stock needs to be removed. Zirconia alumina works well on steels and steel alloys. The composition of this grain makes it fast in cutting through a range of hard metals while enduring high temperatures well—a natural for grinding steel plate. It also has self-sharpening qualities that make the grain long-lasting.
3. Silicon Carbide
For soft metals like aluminum, bronze, brass and iron, silicon carbide is the grain to go with. Unique for its ultra-sharp surface, silicon carbide cuts quickly through these materials. It has the unusual property of fracturing as it grinds to create new edges. This self-sharpening abrasive performs consistently, but is also brittle, which limits its overall durability.
4. Ceramic Aluminum Oxide
Considered the premier abrasive, and sometimes referred to as simply “ceramic”, this grain is the pick for hard metals. It grinds titanium, stainless steel and armored steel well. Hard, strong and self-sharpening properties make ceramic aluminum oxide high performing and long-lasting. The grain’s tendency to micro-fracture controls temperatures in moderate to high heat and creates new, sharp edges as old ones break.
Grinding Wheel Grit: Particle Size Matters
Once the abrasive has been decided, the second step is to determine the grit number. Grit refers to the coarseness or fineness of the abrasive particles that compose the grinding wheel.
Grit is important because the wrong choice can damage the part being worked on by being too harsh. Or if the grit chosen is too fine, it can make the time spent on a project longer than it needs to be.
So how is the grit of a grinding wheel determined? Grit is measured through the process of sifting abrasive particles through a screen. A 10-grit grinding wheel is made up of abrasive particles that were sifted through a screen with 10 holes per inch and a 120-grit wheel is comprised of ones that were sifted through one with 120 holes per inch.
Modern Machine Shop breaks grit down this way:
- Coarse grit wheels are lower numbers such as 10, 16 or 24
- Fine grit wheels have higher numbers such as 70, 100 and 180
A coarse grit wheel removes metal at a high rate. The large particles rip off bigger pieces of metal. Although it cuts faster, the finished product will be rougher. When the finish of the workpiece does not have to be super smooth, or a large area needs to be grinded, coarse grit is appropriate. A coarse grit is also best for soft metals like aluminum or soft steel.
Choose a fine grit wheel when the smooth finish of a work piece is important, when the grinding project requires precision, or when a smaller area is being grinded. A fine grit is also best for brittle materials like glass or brittle metal because a fine grit reduces the risk of chipping.
Grinding Wheel Bond: Invest in the Right Texture
The grinding wheel bond, or grade, refers to the material that holds abrasive particles together. The bond determines the cut rate by exposing new abrasive particles as the grinding wheel is used. As particles wear out, they fracture and newer, sharper particles become exposed in their place.
Bonds determine whether the grade of a grinding wheel is hard or soft, and choosing the right grade is critical to the success of any project involving metal grinding. Grade is expressed according to the letters of the alphabet with A denoting soft and Z indicating hard. Norton Abrasives breaks it down like this:
- Soft grades range from D through H
- Medium grades range from I through P
- Hard grades range from Q through Z
A soft grade is the best choice for hard materials like carbides or hard tool steels as well as for grinding large areas. You want a soft grade for projects where finish is not as important as efficiency in rapidly removing a lot of materials. This is because new grains get exposed as you work.
A hard grade is the way to go when grinding soft metals or when working on skinny or small surface areas. Hard grade grinding wheels have a longer useful life because abrasive particles are held together with a stronger bond. That stronger bond also means new grains that are sharper are slow to be exposed as you work.
A variety of substances are used to hold abrasives together. Vitrified bonds are a mixture of clay that is fired at high temperature to fuse abrasives in place in molten glass. These bonds are very hard and brittle. Resinoid bonds hold abrasives together with synthetic resin. Synthetic resin softens during grinding from the heat generated. Other bonds that are regularly used include shellac, rubber and silicate (glass).
Grinding Wheel Types: Shape Your Success
Grinding wheels come in shapes to match the many types of grinding jobs out there. They are often referred to by types. The type simply refers to the shape. Sizes, diameters, thicknesses and the sizes of arbor holes vary as do the grit, abrasive and bond. Here are six of the most common types.
Type 1 – Straight Grinding Wheels
The type 1 grinding wheel is a general-use wheel type. Type 1 wheels are sometimes referred to as “snagging wheels.” They typically have a 2-inch to 4-inch diameter. Their size makes them ideal for grinding off excess metal in a range of circumstances.
Often called “cup wheels,” type 11 grinding cup wheels have an advantageous shape with abrasive material on the sides for grinding, finishing and cutting metals, glass, plastic and other materials. These grinding wheels are used for smoothing weld seams, preparing surfaces for plating or painting and cleaning castings.
Type 27 – Flat Depressed Center Wheels
This grinding wheel type has a flat profile with a depressed center to keep the mounting hardware out of the way during operation. A depressed center allows for clearance when the operator must work at a constrained angle. Often used in the grinding of castings, weld beads, flash or parting lines, and metal part defects.
Type 28 – Concave Depressed Center Wheels
Type 28 grinding wheels, also known as “saucer wheels,” have similarly depressed centers and are optimized for low grinding angles. They differ from type 27 wheels in that their concave or saucer-shaped design allows for better access to the workpiece — especially in tighter areas, such as corners, fillets and overhangs — and increased aggression at smaller working angles.
Type 29 – Conical Depressed Center Wheels
A type 29 grinding wheel has a slightly angled or conical shape. This makes it useful for contouring and shaping surfaces. The angle of type 29 wheels also makes them good for more aggressive grinding.
The type 42 cutting wheel is flat with a depressed center like the type 27 grinding wheel. The type 42 is thinner though, so it can be used for slicing through metal. This design gives the operator a clear view of the cut and it enables the operator to perform a flush cut because the raised hub enables the locking nut to be recessed and kept out of the way.
Metalworking Success Starts with the Right Grinding Wheel.
With the right selection and supply of grinding wheels, your shop can experience more success on metalworking projects. A well-stocked tool crib means less downtime waiting for parts and fewer missteps resulting from using the wrong part for the job out of frustration or impatience.
Make foresight your philosophy. Talk to your team at Imperial Supplies about the optimal mix of grinding wheels, cutting wheels and sanding discs for your shop. With a sharp supply of the right tools, you’ll have what you need to make every machining project perfect.