Four factors to consider when purchasing a grinder: You get what you pay for

STAMPING Journal July/August 2001
July 26, 2001
By: David Smith

Cost often is a deciding factor when you purchase a grinder. However, the saying "you get what you pay for" can be true when you're talking about tools. The price tag alone doesn't always reflect some of the more important factors--performance level, cost to operate, and tool life--that make a grinder worth its cost.

Cost often is a deciding factor when you purchase a grinder. However, the saying "you get what you pay for" can be true when you're talking about tools. The price tag alone doesn't always reflect some of the more important factors—performance level, cost to operate, and tool life—that make a grinder worth its cost.

Four points to examine to help you determine a grinder's value include its output power, torque, motor quality, and safety features.

Power In Does Not Necessarily Equal Power Out

Input power, or the amount of power a tool needs to operate, can be misleading in judging the efficiency, power, and ultimate value of a grinder. A grinder may have an input power of 750 watts, but this number does not necessarily translate to actual grinding power. When a tool is used, power is lost through heat from several areas of the tool, such as the cord, wiring, and motor. This decreases the overall power used for operation of the tool.

The 750-watt-input grinder mentioned previously may lose more than 100 watts of energy as power travels from plug to motor. So, the grinder may be using only 300 watts for actual tool operation.

A more telling number to determine a grinder's performance level is its output power, or the power used for tool operation after heat loss. A tool with an output power of 750 watts ensures that 750 watts will be used to operate the tool.

Tools with features to prevent heat loss, such as ball and needle bearings, high-efficiency fans, and extra-insulated cords, generally will lose less power from plug to spindle, resulting in increased available power for tool operation.

Speed Is Nothing Without Torque

Tool speed and torque—the turning force of a grinder—reveal much about a grinder's power. The no-load tool speeds of most grinders likely are the same. However, the amount of stock removed per rotation of the grinding wheel is directly proportionate to the amount of force (torque) with which the wheel spins.

For example, two grinders each may have a no-load speed of 10,000 rotations per minute (RPM). The grinder's torque determines the tool's RPM under load conditions. The grinder with a higher turning force more easily can maintain a high speed of rotation when under load conditions. The RPM of the lower-torque grinder greatly decreases when put under load conditions.

Ultimately, grinders with higher torque are able to remove more stock over a fixed period of time.

Kill the Motor and the Tool Is Sure to Follow

The most important component of a grinder is its motor—it makes the tool run.

Foreign matter, such as masonry dust, can enter the motor of a grinder through air inlet and outlet openings. As matter impacts the rapidly rotating blades of the fan, part of it can be thrown against the armature windings, eroding the insulation on the winding wires. Other factors, including the intense heat produced by grinding, often make a grinder's motor the first thing to quit when the tool dies.

The number and types of features incorporated into a grinder's motor go a long way toward determining the tool's overall life. Winding protection—a grid that deflects debris from the motor as it enters the tool—can make the tool resistant to the wear associated with grinding.

Other features, such as coating on the field coil, can help to prevent overheating of the motor under heavy loads.

Safety First

Human flesh can suffer a great deal of damage from the intense friction caused by grinding. Further, the high levels of torque associated with grinding present the problem of backtwist torque if the abrasive wheel strikes an obstruction.

Because of these potential dangers, grinders that have innovative safety advantages often can be worth the extra dollar. Although almost all grinders include wheel guards as standard equipment, some users are so inconvenienced by the time it takes to adjust a wheel guard with tools that they sacrifice their own personal safety by removing them altogether. It's worthwhile to identify those grinders on the market that offer toolless wheel guard adjustment, providing safety and convenience for the operator. A slip clutch can further help to protect the user from excessive backtwist torque, while also helping to prevent damage to the tool's geartrain.

Finally, any operator using a corded tool runs the risk of electric shock. Double insulation on a tool protects against electric shock by creating a nonconducting barrier between the operator and the electric components inside.

Ergonomic design is an innovation that has spread not only throughout the grinder market but also across the entire power tool industry. An ergonomically designed grinder enables both right- and left-handed operators to hold the tool more comfortably. In addition, two-position side handles, which can be screwed into the left or right of the gear housing, allow for a better overall grip.

Operator comfort means less fatigue, decreasing the overall chance of injury, not to mention increased efficiency.

Making a Confident Purchase

Lower-priced tools can meet all of the criteria mentioned previously. Conversely, a high price tag on a tool does not always guarantee high quality.

Knowing what features to look for and evaluate should help you make a confident purchase. Only then will you be getting what you pay for.

David Smith

Contributing Writer
Metabo Corp.
1231 Wilson Drive.
West Chester, PA 19380
Phone: 610-436-5900

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STAMPING Journal is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping.

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