Operation Optimize

A better understanding of the relationship between abrasives and power tools leads to higher productivity and cost savings


When choosing the right abrasive and power tool combination, it’s important to have a good understanding of the application and the desired outcome. Knowledge of the type of material and size of the cutting or grinding application, such as depth and square footage, is essential. It’s also important to know the surface finish requirements and the cost and time available to complete the job.

Metabo has made the decision-making process for pairing abrasives and tools easy and straightforward by color coding its recommended and optimized systems.

Depending on these specifications, the choice of the best abrasive and tool for the job can be optimized. This article reviews the decisions that go into developing an optimized solution for specific applications, which can have a dramatic impact on productivity and the total cost of the project.

With so many product options on the market, Metabo simplifies the process for pairing abrasives with angle grinders by providing customers basic guidelines like the one seen here.

A lot of variables are involved in pairing abrasives with an angle grinder for an optimal result. Metabo categorizes three major tool system types as: heavy duty, super duty and extreme duty. In most applications, these general guidelines are effective for choosing the right grinder for the application and saving the operator a lot of trial and error.

Abrasive Shape And Size

Before diving into a project, an operator needs to determine what type of abrasive to use: a cutting wheel, grinding wheel, flap disc, wire wheel brush or resin fiber disc. It’s important to note that a cutting wheel should only be used for cutting material to length. For removing material, there are several options, depending on the task.

Grinding wheels are the most aggressive, least comfortable to use and leave the surface unfinished. Flap discs are more comfortable to use, remove material almost as aggressively as a grinding wheel and allow the operator to finish and blend a working surface at the same time.

Resin fiber discs have a wide range of available grits, which allows for more flexibility when achieving a specific surface finish. Resin fiber discs need to be paired with the right type of backing pad for each desired outcome. Wire brushes are meant for surface prep tasks and not used for material removal.

The operator also needs to know the size of the abrasive required for the job. Depth of cut, operation and material thickness dictate the diameter requirements for a cutting wheel. Size of the working area or the amount of material being removed helps determine the diameter requirements for flap discs, grinding wheels, wire wheel brushes and resin fiber discs.

A general rule of thumb is that larger diameter abrasives are more efficient and help to save operating costs by increasing the speed of removal or cutting and by reducing the amount of time spent changing abrasives. On the other hand, “too much tool” can sometimes be overkill and increase user fatigue due to the weight of the tool. Or, it might be too large to fit into tighter working areas. The most important thing to remember when choosing abrasive size is the tool’s maximum RPM rating.

Never use a product that is rated at lower RPMs than the angle grinder being used. In other words, do not put a larger abrasive product on a smaller angle grinder to try and get into a tight place or to reach a difficult working area. Rather, specialized tools can help solve problems like this, such as Metabo’s flathead angle grinders.

Best practice also includes following the safety specifications on the label of the abrasive product and the manual of the angle grinder.

Before diving into a project, an operator needs to determine what type of abrasive to use: a cutting wheel, grinding wheel, flap disc, wire wheel brush or resin fiber disc.

Abrasive Grain

After determining the size of the abrasive, the next step is understanding the type of material being worked. Knowing the type of metal and its hardness helps in choosing the abrasive compound and special additives required to accomplish the job as easily as possible. The type of material also determines the right type of abrasive grain to use.

A breakdown of various abrasive/tool scenarios helps to reveal where fabricators can find cost savings and increased productivity.

Not all abrasive grains are created equal, and additionally, the quality among the grain type can also change. In some cases, depending on the product’s purpose, grains can be blended to accomplish a different result. A good abrasive product has self-sharpening characteristics that allow the abrasive to remove material effectively. Less advanced grains have little or no ability to self-sharpen.

In order for an abrasive product made with a non-self-sharpening grain to continue to cut material, the bond holding the abrasive grains together needs to be a softer formulation, reducing the life of the abrasive. It is very difficult to get a low-quality abrasive grain that is aggressive and long lasting because they have an inverse relationship. Higher quality abrasive products can be both aggressive and long lasting because the grain itself is harder and self-sharpening and a strong bond holds the grains together.

Four main synthetic abrasive components are used to make the most common abrasive grains: silicon carbide, aluminum oxide, zirconia alumina and ceramic. Silicon carbide grain is used for masonry and non-ferrous metals, softer metals and ductile iron. Silicon carbide has a self-sharpening characteristic.

Aluminum oxide is the most common and affordable abrasive grain and works well on mild steel and light stainless steel. Aluminum oxide grain does not have a self-sharpening characteristic, so these abrasive products must be made with a softer bond to release the old abrasive grain and expose new sharp grains.

Zirconia alumina works well on steel, stainless steel and hardened alloys. Zirconia alumina is the least expensive option for a self-sharpening grain.

Ceramic offers the highest level of performance on steel, stainless steel and hardened alloys. Ceramic grain is incredibly strong, sharp and hard. It lasts a long time with extremely fast cutting and a high material removal rate while being able to handle the toughest applications. Ceramic grain is, expensive but can make the most economical sense when used in tough applications because its performance provides unmatched productivity gains.

Abrasive Grit and Type

In addition to grain type, other factors that can determine the aggressiveness and speed of an abrasive product include the thickness (cutting wheels), grit (cutting wheels, flap discs, grinding wheels and resin fiber discs) and gauge (wire brush filament). In terms of cutting wheels, the thickness influences the speed of the cut and the life of the wheel. For flap discs, grinding wheels and resin fiber discs, the lower the grit number, the more aggressive the abrasive. Grits can range from coarse (16) to fine (2,000). The most common grits are 36, 40, 60, 80 and 120.

When choosing a wire wheel brush, the thicker the gauge of the wire filament, the more aggressive the wheel. A wire wheel’s level of aggressiveness also changes based on whether it is a crimped or knotted wire wheel. Knotted wire wheels are more aggressive than crimped because they increase the density of the wires while crimped wire wheels are better at conforming to the working material.

Grinder Considerations

With a general understanding of how to choose an abrasive and knowledge of the material being working on, the determination of the right angle grinder for the job can be made. As the hardness of the material increases, the performance requirements of the abrasive also increase. When a higher performance abrasive material is required, providing the right amount of power to the abrasive is key to improving work output and cost minimization.

To produce optimal results, Metabo provides a basic guideline for pairing abrasives with angle grinders. To find a quick solution for an optimized system, match heavy-duty abrasives with heavy-duty machine options and super-duty abrasives with super-duty machines. Be sure to also check the tool’s RPMs and always use the right guard for the abrasive shape type (Type 1 or 41, 27 or 42, or 29). In addition, power and torque are two major considerations when choosing the tool for the application.

Torque is especially important when working with an abrasive or on a material that produces a high level of friction. As the abrasive’s aggressiveness increases, whether due to increase in grain coarseness or working surface area exposure, more torque is required to keep the abrasive moving at the right speed. A lower grit abrasive, harder metal or alloyed metal can also require more torque.

Regardless of the torque or gearing of the angle grinder, if the abrasive is not provided with the right amount of power, the removal rate will not be optimal. As an angle grinder is used with more force, more amps are drawn from the power source because of increased resistance and friction. If the abrasive is not provided ample power, the operating speed of the abrasive cannot run fast enough and can be compromised by glazing over.

This happens when the working material adheres itself onto the abrasive and covers the grain, preventing it from continuing to remove material. When this happens, it can sometimes be salvaged, but often times, it is best practice to replace the abrasive.

Metabo’s higher end angle grinders feature electronics that reduce and prevent underpowering abrasives. The Tacho Constamatic feature, for example, helps abrasives run at a nearly constant speed (like cruise control on a car).In addition, electronics also increase operator safety and prolong the life of the tool by improving machine temperature control.

Regardless of the torque or gearing of the angle grinder, if the abrasive is not provided with the right amount of power, the removal rate will not be optimal.

By The Numbers

To understand how an “optimized system” impacts a job, consider the following scenarios as an example:

Two identical worksites each have 50 workers on the job with each worker being tasked to grind 100 lbs. (5,000 lbs. total) before the job is complete. Assume that the labor rate is $75 per hour (a conservative estimate) and that both worksites are using the same angle grinder. Also assume that jobsite A is using a low-quality zirconia alumina abrasive and jobsite B is using a premium zirconia alumina abrasive.

Over the years, Metabo has developed several visual guidelines to help its customers make the best decisions when pairing tools with abrasives.

Jobsite A’s basic zirconia abrasive costs $2.75 per piece, removes 0.8 oz. per min. and needs to be replaced every 75 oz. of material removed. Jobsite B’s premium zirconia abrasive costs $3.50 per piece, removes 1 oz. per min. and needs to be replaced every 100 oz. of material removed.

Although abrasive A is cheaper than abrasive B by $0.75 per piece, it takes 1,067 pieces of abrasive A or 800 pieces of abrasive B to complete the job of removing 5,000 lbs. When comparing the purchase cost for the above quantities, abrasive B ($1,648 per job) ends up being less expensive to use than abrasive A ($1,728) for completing the job. Abrasive B’s grain quality is better, removing material at a faster rate per wheel.

The benefit of using the right abrasive product for the job is magnified when considering the costs of labor. In this case, abrasive B saves about $25,666 on labor costs ($127,666 vs. $102,000). Considering the acquisition and labor cost, abrasive B is ahead of abrasive A.

Jobsite B has now chosen a “quick” toolless abrasive changing system (Metabo patented) that reduces the changeover time from 2 min. to 1 min. Metabo has also been able to reduce average abrasive changeover times down to 20 sec. via the Metabo Quick System. When applying a toolless change system to the right abrasive choice (abrasive B), another $1,000 in labor costs can be saved.

There are also additional hidden benefits of using a system like the Metabo Quick System, including reduced time spent searching for spanner wrenches, reduced user frustration and more time spent “in the zone” and away from workplace distractions.

Metabo angle grinders offer long life and significant user safety in part due to their mechanical disc brake and deadman switch, which causes the disc to stop in 2.5 sec. after release, even during a power failure.

Unsurprisingly, a better and more aggressive abrasive requires a higher performance tool that provides speed stabilization and increased power. Pairing a high-performance tool with cruise control electronics provides more power to the abrasive in demanding situations, resulting in impressive performance and productivity gains.

This type of tool increases the rate of removal on an abrasive product because of the increased power fed to the abrasive. If the electronics allow enough power to remove 0.1 oz. more per min., the cost of the job could drop by an additional $9,091.

When choosing to work with an optimized system, the savings are dramatic over the total cost of the ownership. In the case above, one jobsite was able to complete the job and save $35,837 on abrasives and labor.

A major advantage for Metabo is its position as one of few vertically integrated manufacturers still making the vast majority of its components in-house and controlling the formulations of its abrasives. This enables Metabo from the very beginning of tool development to create optimized systems. When stuck with the choice between what abrasive and angle grinder to use, Metabo has made it easy to decide by pairing its angle grinders and abrasives for an optimized system.

There are clear cost saving benefits when choosing to optimize angle grinders and abrasives. In a competitive marketplace, this choice can be the determining factor on whether or not business is won and profitable.

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