How to Select the Right Flap Disc for Your Project

Are you exploring flap discs to use for your next project? Maybe you’ve been using grinding wheels all this time and have overlooked the benefits of a flap disc. Flap discs are highly versatile tools and can meet your needs in a variety of applications — from stock removal to grinding and finishing. Many operators actually prefer flap discs over grinding wheels during operation, and when it comes to your next project, flap discs may be just the solution you need.

Keep reading our flap disc buying guide to learn more about these tools and how to select the right flap disc for your project.

What Are Flap Discs?

Flap discs are made from multiple overlapping pieces of abrasives or ‘flaps,’ which is how they got their name. Flap discs are designed for right angle grinder applications ranging from heavy stock removal to surface blending and smooth finishing.

While the first abrasive flap discs for high-speed angle grinders were developed towards the end of the 1970s and were somewhat basic, today’s versions offer an array of diversity. You should strongly consider a flap disc over a grinding wheel if you need a superior finish and greater ease of use during operation.

Advantages of Flap Discs

Flap discs are versatile: they can grind, blend and finish. They are also lightweight, easy to maneuver, and require less change over time. When performing a job, many operators prefer flap discs over grinding wheels due to lower vibration and noise levels. Plus, they offer cooler cutting with minimal scratching.

For instance, grinding wheels have to be discarded even after a small area of abrasive is worn out. Comparatively, flap discs remain useful even after the flaps erode, which results in a longer operating life. Compared to a flap disc, grinding wheels are cheaper on a unit cost basis. However, if you consider the versatility, durability and ease of use provided by flap discs, they are more cost-effective in the long run. Because of these advantages, the popularity of flap discs has soared in the last several years.

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How to Select the Right Flap Disc

When it comes to flap discs, there’s a variety of discs available in today’s marketplace. Let’s start by understanding the various components of a flap disc, so you know how to select the right disc for the right task:

Flap Disc Shape

Is stock removal your primary objective, or do you want a smooth finish? Choosing the right disc shape is the single-most important variable, and the shape will help you effectively achieve your results. Flap discs are almost always used on right angle grinders, and they are applied to your work at an angle or parallel to it. Flap discs are available in two shapes: conical or flat-shape.

  • Conical flap disc: Conical flap discs are your best friends when you need to remove a lot of material in a small amount of time. They can be used for edge-working as well as on contoured applications. The flaps in a conical flap disc are angled. As a result, these discs offer a greater surface area for stock removal on horizontal surfaces.
  • Flat flap disc: While conical discs are great for rapid stock removal, flat flap discs are best for blending and superior finishing. They are mostly used on flat surfaces. The flaps of a flap disc are adhered to a backing plate which provides stability during operation.

Flap Disc Material





The backing plate material is also an important variable to consider when choosing flap discs for your application. Fiberglass, plastic and metal are the most popular backing plate materials:

  • Fiberglass: Being strong, durable, lightweight and safe, fiberglass is the most popular material choice. Fiberglass creates a strong bond with adhesives and does not contaminate the working surface. This type of plate also gets consumed during use, and it absorbs vibration very well. Remember, fiberglass backing is made out of layers of fiberglass that are mesh-bonded and pressed together. With more layers and a higher mesh density, the backing will be stronger and more durable — this is an important consideration when you’re examining the detailed specs of a flap disc.
  • Plastic: Another popular backing material is plastic, and nylon is the most commonly used plastic. These backings can be trimmed which allow longer usage of flaps, specifically during blending and finishing. These days, plastic is becoming an increasingly attractive choice due to its conformability and costs.
  • Metal: Metal backing plates are the safest choice, and they’re great when you need extra strength and firm support. Aluminum is a commonly used metal. Since metal plates are expensive, they should also be used where they make the most sense. For example, when working with flap discs on concrete or stone applications, use flap discs with metals for strong support and better performance. Metals don’t get consumed during use, but metal plates can be easily recycled when a flap disc is past its useful life.

Abrasive Flap Densities

What does abrasive flap density mean? Think of the density as the total amount of abrasive area provided by the flaps on a flap disc. This area depends on the quantity of flaps on a disc, their angle relative to the center of the disc and how far they are spaced. Remember, each variable can impact the amount of disc area available to work on your job.

  • 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

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 Grit Chart

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 aluminumCompared 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 woodFlap 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.

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.

Purchasing Your Flap Discs

When it comes to purchasing flap discs, you have plenty of options. However, a reputable company that cares about you and your project will help you experience a better result. You should also feel comfortable asking for samples when you’re trying new tools like a flap disc.

National Abrasives, Inc. has a large variety of tools, accessories and supplies to meet your immediate needs and your needs in the future. We’re a family owned company that offers same-day shipping and discounted pricing for bulk orders. Browse our large selection of brand-name flap discs, including Walter Abrasives flap discs, along with angle and bench grinder tools and accessories. If you have any questions, our team can guide you to the right tool for your specific job. Contact us today to get started!

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*Updated: February 20, 2020

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