Maximizing abrasive performance when cutting or grinding tube

When cutting square tubing, maximize cutting performance by entering from a corner.

The terms pipe and tube often are used interchangeably, but there are differences in how they are made, sized, and used. By definition, pipe is used for transporting and delivering gases and liquids, so the ID is a critical dimension. In addition to ID, pipe is sized by its schedule, which refers to wall thickness and is related to the pressure rating. Regardless of the size, pipe is always round.

Tube is available in a variety of shapes and sizes. Because tube is used in mechanical, structural, and decorative applications, the OD is critical, as is the wall thickness, which corresponds to its strength.

As with any cutting and grinding application, working with tube presents its own set of challenges, so it's essential to implement some best practices to achieve the best performance. The wall thickness, profile, and material are all important factors to consider when selecting the right abrasive for the job and for optimizing its performance.

Tube typically is sourced and fabricated using small diameters, usually just a few inches, whereas pipe diameters of several feet aren't uncommon. Because tube typically is small in OD, cutting it with abrasive wheels is more efficient and cost-effective than for pipe. Abrasives also are commonly used for a variety of grinding, blending, and finishing applications.

The first question to ask when cutting or grinding tube is, "What am I trying to accomplish?" Selecting an abrasive product that is best-suited for the hardness and thickness of the material is key to optimizing performance and product life.

Abrasives generate heat, which can affect the overall result and finish. When working with thin-walled tube, consider abrasives that are less coarse to minimize heat and aggression. A 60- or 80-grit flap disc or a coated abrasive would be a good option in this case versus a hard-bonded grinding wheel. Flap discs, for example, are easier to control and reduce the risk of removing too much material and compromising the integrity of the tube.

When cutting or grinding on hard material, consider products that are softer and therefore more conformable for the operator to use. Running a hard wheel on hard material can cause the wheel to chatter and jump, making it more difficult to control and limiting wheel performance. Instead, a cutting wheel with a softer bond provides faster, smoother cuts on harder material.

Another consideration is product size. When cutting tube that is larger than 11⁄4 or 2 inches in diameter, a 41⁄2-in. cutting wheel does the job, but upgrading to a 6-in. cutting wheel is a better choice. Using a larger-diameter wheel on a larger-diameter tube helps reduce downtime for changeover and maximizes product life, which reduces operating costs.

It's important to understand what an abrasive product is designed to do and the potential benefits of choosing one product over another, rather than trying to force the wrong product to work in an application it wasn't designed for.

Coated abrasives typically are more effective for grinding tube than hard grinding wheels are, since tube generally has thin walls. The following three product types are used commonly in tube grinding applications:

Grinding at lower, shallower angles extends wheel life but decreases the cut rate. Conversely, grinding at steeper angles cuts much faster but wears the wheel more quickly.

Flap wheels can be used to remove a coating, remove burrs, add chamfers, or do a final finish. These wheels are easy to control, are generally less aggressive than flap discs, and are used on a 90-degree edge. However, if the wall thickness of the material is too thin, it can form a sharp edge and damage the abrasive flaps of a flap wheel.

Flap discs are more aggressive than flap wheels and are available in many size, grit, and profile options. They grind and finish in one step, saving time and money.

Resin fiber discs are quite aggressive for grinding and are less expensive than flap discs; however, they are less durable and require more frequent changeover. The discs are paired with backing pads—available in soft, medium, and hard—that allow the operator to conform them to a specific part or application for the best performance.

Another consideration that can have a significant effect on performance is profile or shape. Cutting wheels, for example, are available in Type 1 and Type 27 profiles. Type 27 wheels have a depressed center, and while they can be used to cut tube, they generally are not the most efficient choice for any extruded or radius material. The depressed center reduces the effective cutting surface and creates a potential interference point.

Type 1 wheels, which have a flat profile, generally are more effective for cutting in tube applications. They provide versatility, durability, and maximum cutting surface, which can extend their overall life.

Following some key best practices can help optimize performance when cutting and grinding tube:

Use the Appropriate Pressure. Allowing the abrasive to do the work without pressing too hard helps extend product life and optimize performance. Putting excessive pressure on the tool causes the abrasive to dull faster and can result in product failure due to increased heat, friction, and stress. It also increases the risk of binding, which is a potential safety hazard. When an operator feels the need to use more pressure to get the work done, it could be that the wrong product is being used for the job. For cutting, use light pressure and a consistent, rocking motion through the cut. This minimizes friction and allows the wheel to pull itself through the material.

Watch the Angle of Approach. Cutting wheels are designed to be used at a 90-degree angle to the workpiece. Straying too much from that orientation can cause friction and heat buildup that cause the wheel to break down.

Grinding wheels offer versatility for angle of approach. Grinding at lower, shallower angles extends wheel life but decreases the cut rate. Conversely, grinding at a steeper angle cuts much faster but wears the wheel more quickly. When choosing a flap disc, it is important to allow the entire width of the flap to contact the workpiece for maximum performance. Lower grinding angles—5 to 10 degrees—are recommended when using a Type 27 flap disc for lighter-pressure blending and finishing applications. However, steeper angles—15 to 25 degrees—are more appropriate for stock removal and aggression. For these applications, a Type 29 angled flap disc is a better choice.

Prioritize Safety. No matter the cutting or grinding tool, always use the tool guard to help reduce the risk of operator injury. For the best cutting wheel performance, it is important that the wheel is rotating and pulling itself into the workpiece rather than away from the workpiece.

Knowing the desired outcomes for the application and understanding the level of performance that an abrasive product can provide for the material are key steps in getting the most out of cutting and grinding products. Performance can be significantly improved by properly matching the abrasive product to the thickness and hardness of the base material, as well as using the product as it was designed.

Rick Hopkins is senior product manager – metal fabrication for Weiler Abrasives, 1 Weiler Drive, Cresco, PA 18326, 800-835-9999, www.weilerabrasives.com.

For maximum cutting performance, properly clamp the tube and position the cut line as close to the clamp point as possible to minimize vibration, chatter, and the risk of binding.