• Standard density: Standard density flaps are optimal for fast stock removal and heavy-duty applications.
• High density: High density flaps are best-suited when working on curved or uneven jobs, as well as during finishing. Don’t take the description of flap disc density at face value. Consider the number of flaps, angle and spacing to differentiate between two discs, both of which may specify “standard density flaps” or “high-density flaps.”

Abrasive Grit Material

Abrasive grit types

Flap discs can be used for a variety of applications, whether it’s metal or woodworking, concrete grinding or finishing, stone smoothing or finishing, paint or rust removal, and more. In order to get the maximum benefits out of flap discs, it’s important to choose the right abrasive grit material for your specific job needs. Let’s look at the most commonly used abrasive grit types:

• Ceramic Alumina: This material is great for stainless steel or alloy metals application. With Ceramic Alumina, the grit material ruptures at a micro level during operation. This produces a constant supply of sharp cutting surfaces. As a result, it enables faster cutting while allowing the entire grain to be used. As the entire grain is getting used up in the cutting process, these discs offer higher durability.
• Zirconia Alumina: This is a blend of Zirconia and Aluminum Oxide grain, and it’s great for carbon and mild steel application. Zirconia Alumina costs less than Ceramic Alumina, and it provides a great cut rate for the cost.
• Aluminum Oxide: This is the original grit material used in the 1970s when flap discs were first introduced. It’s also the lowest-cost option. Today, it is recommended for smaller jobs where the product being produced is low-value.

Grit Size

You’re probably familiar with grit size if you’ve been using grinding wheels. Grit size is the final variable you have to choose based on your ultimate goal and what you’re trying to achieve. For stock removal or common grinding, use abrasives with lower grit numbers. On the other end of the spectrum, use higher grit sizes if you’re trying to achieve smooth finishing.

Flap Disc Uses

Flap discs initially became popular for use on metals, especially in welding applications. Today, various flap discs are available to use for different surfaces:

• Flap discs for aluminum: Compared to other metals, aluminum has a lower melting temperature and melts easily. This causes the aluminum material to coat the flap disc during grinding, covering the grit and exposing only bits of aluminum. For stock removal, use a T29 conical disc at a 15-degree angle to provide maximum surface contact. If you need to surface-clean or provide a smooth finish, use a T27 flat disc that’s parallel to your work area. For best results, use light and even pressure to optimize the grinding process and reduce loading.
• Flap discs for wood: Flap discs are great tools for working on wood. The flap discs designed for use on wood are similar in nature to the ones designed for use on metal. You can use aluminum oxide grits for wood applications. For wood, you should also use the flap discs on your angle grinder just like you would use a grinding wheel. In order to avoid deep scratches, start with a heavy grit and work your way up to the lighter grits (100+) for a final finish. For wood sanding, work your way through 120, 150, 180 and 220-grit sizes to achieve a furniture-grade surface.
• Flap discs for paint removal: Do you have a metal object that’s rusted but you know you can still extend its life? Do you have old, chipping paint on your car that you need to remove to give it a like-new appearance? Flap discs, especially non-woven discs, are ideal tools for removing paint and rust. Non-woven flap discs, or the ones with aluminum oxide, can be used for paint or rust removal applications. As with flap discs in general, these discs can grind and finish in a single operation while offering a smooth and controlled grind.
• Flap discs for concrete: You’ll need silicon carbide or diamond flap discs for aggressive stock removal on concrete. Silicon carbide and diamond are some of the hardest materials in the world. Using these discs will allow you to work on concrete surfaces without the need for high pressure. These flap discs have rigid backings, and they can also be used on other surfaces such as engineered stone, granite, marble and ceramics.

Flap discs on surfaces

Getting Started With Your Flap Discs
Before you start using any shop tool, you should always make sure you:

• Understand your tool
• Read the user’s manual
• Wear the proper safety equipment
• Ensure a safe working area
• Know what you’re using your tool for

With flap discs, you need to consider the size and scope of your project. Do you have to remove stock aggressively, or is smooth finishing your goal? Or do you want a grind that’s somewhere in between? Whatever your answer, there’s a flap disc that’s right for your situation.

Don’t limit flap disc to the common metals. Flap discs can also be used across various surfaces, including aluminum, wood, concrete, engineered stone, granite and more. For each of these applications, whether you’re grinding or finishing, make sure you choose the right flap disc. Remember, conical shaped flap discs are great for stock removal and flat flap discs are best for finishing.

Flap disc backing material is important as it provides support during operation. Use metal backings for concrete or engineered stones, and use fiberglass or plastic backings for most metal or wood jobs. Also consider your abrasive grit material, and choose your grit size to achieve the desired results. For common grinding, use abrasives with lower grit numbers. For smooth finishing, use higher grit sizes.

Using a flap disc instead of a traditional tool can greatly enhance the quality of your job. You can also benefit from lower noise and vibration. Flap discs can lead you to a world of new applications, while helping you achieve new levels of efficiency and effectiveness.