By Tony Hufford, category manager – metal fabrication, and Rick Hopkins, technical training manager – metal fabrication, Weiler Abrasives
These products come in a variety of sizes to provide optimal grinding surface contact in specific applications found in fabrication shops, foundries and shipyards.
As with other abrasives, proper and safe use of cups, cones and plugs can affect product performance as well as productivity and the end result.
The benefits
Cones and plugs are not designed to polish or provide a final finish. Rather they are used to remove material quickly and efficiently in holes, bores, corners, fillets and tight areas that other abrasives can’t reach.
Cups are not designed for use in tight or constrained areas like cones and plugs are. They’re designed for removing a lot of base material quickly and are ideal for heavy metal removal, grinding, transitioning, rough beveling and removing cracks or flaws.
Cones and plugs are all about versatility. With the ability to pivot, they can get into tight spaces and smaller internal diameters rather than being constrained for use only on the outer diameter of a workpiece. A cone’s diameter gets smaller from base to tip. Some cones have flat sides that taper, and others are more rounded from the base to the tip, often in a bullet shape. These are ideal for getting into fillet welds and tight corners. The tapered end can be used to pivot in tight spaces while still maintaining an acceptable level of surface contact.
Plugs have a flat side with a consistent diameter, making these products ideal for grinding flat surfaces. Operators can hold the plug flat with their hands away from the work piece to remove the material linearly, maintaining an even, consistent contact patch.
Cups, cones and plugs come in a variety of profiles, diameters, thicknesses and materials.
Type 11 cups — sometimes called cup rocks, cup stones or flaring cups — taper outward from the top of the cup to the bottom. They are used on right-angle and high-frequency grinders and are most commonly available in diameters from 4 to 6 inches, with the diameter specifying the widest part of the cup at the grinding surface. Thickness, which describes the height of the cup or how deep it is, is usually 2 inches for these products. These products are available in 5/8-inch, 11 threaded arbors.
Cones and plugs are available in numerous shapes and sizes; the most common being Type 16 cones, Type 17 cones, Type 18 plugs and Type 18R plugs. A Type 16 cone is shaped like a bullet with a rounded nose, while a Type 17 has a flat nose and tapered sides. A Type 18 plug is a cylinder with a flat top, and a Type 18R is the same cylinder with a rounded nose.
With cones and plugs, the base side or the diameter is typically 1 to 3 inches and the length is typically 2 to 3 inches. These products are available in 5/8-inch-11 and 3/8-inch-24 threaded arbors. Resinoid bonded materials are common in the design of cups, cones and plugs, as they deliver a good combination of durability, performance and value.
Common mistakes
While these are versatile products, there are some challenges and common mistakes operators may make that can hamper performance and affect their lifespan.
The biggest issue is using the wrong angle of approach, which can result in the loss of large pieces of the abrasive. Cups, cones and plugs are not designed with fiberglass reinforcement. If they start wearing in an unusual pattern due to an awkward angle of approach, it can create a stress-riser and a large chunk may break off.
If the operator forces one of the profiles to do a job it’s not designed for — when it’s not the best profile for the application or the angle of approach — it can degrade the product faster than normal. Choosing the wrong product can force the operator to hold it at an incorrect angle or attack pattern that accentuates wear.
To avoid this, it’s important to choose the right cup, cone or plug for the application, and to use the product at the proper angle as recommended by the abrasive manufacturer.
Another common issue arises when the operator continues to use the product beyond its useful life. Type 11 cups, for example, are typically compressed with two separate layers — a grinding layer of grain and a support layer of grain. Once an operator has worked through the grinding layer, it may appear that there is additional grinding material. However, continuing into the base or support layer will not produce efficient result and can lead to unsafe condition due to lack of support. For cones and plugs, it’s unsafe to use them if they become too small or if the products become hard to control.
Useful life is often dependent on the application. If the product wears to a point where the user has to completely change the angle of attack or efficiency is degraded, the cone or plug has likely reached the end of its useful life for the application. Many times, the end of useful life is determined by the fact that product can no longer effectively reach or access the area. Using pressure and force is never effective and will only lead to undesirable and/or unsafe results.
Just as with any abrasive product used for metal finishing, following some best practices and proper safety procedures can help improve productivity and results while reducing safety risks for the operator.
Optimizing results with cups, cones, and plugs
Abrasive cups, cones, and plugs are available in many styles and sizes, and they can be a great option for heavy material removal or getting into tight spaces. Choosing the right product for the job and using it safely and correctly go a long way toward getting the best results.