An In-Depth Guide to Flap Discs

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Aside from metal fabrication, flap discs can be used in various applications. In every grinding application, it is essential that you choose the appropriate product so you can succeed with the process. In this in-depth guide, we are going to explore everything about flap discs to assist you in choosing the right product for whatever tasks come your way.

A lot of manufacturing applications can greatly benefit from using flap discs. Among the surface conditioning tools such as grinding and cutting wheels, what makes flap discs unique?

Flap discs are also referred to as flapper wheels and are well-suited for angle grinder applications. They offer accurate finishing and blending as well as aggressive stock removal, depending on the operator’s requirements. Additionally, they also provide great maneuverability, versatility, and lesser vibration and noise compared to grinding wheels.

Flap discs are the best option for several applications since they permit the operator to do the finishing and grinding at the same time, saving more time and cost. They can grind like grinding wheels do, however, they are much easier to control. Hence, there is less risk of gouging in the workpiece. You can still use them even a portion of the abrasive wears out since new abrasives will be exposed. Best of all, they are softer compared to grinding wheels and there is less risk of removing a lot of material from the workpiece due to overaggressive grinding.

When opting for angle grinder flap discs, it is important to consider several factors such as the material, shape, density, size, and abrasive grain type. 

What is a Flap Disc?

A flap disc is an essential abrasive that belongs to the laminated abrasive category. These discs are composed of several layered portions of abrasive material overlapping each other. Hence, this is why they are known as flaps. The abrasive grains are attached to the polyester or polycotton material. Then, they are layered and affixed to a backing plate. The backing plate will make the flap disc more stable and provide its own essential properties to the product.

What Are the Different Backing Plates for Flap Discs?


If you require a high degree of flexibility, then you can use this backing material for your flap discs. It can greatly help in minimizing the level of vibration generated, which is a perfect option for uneven surfaces. Additionally, some plastic backing plates are trimmable and color-coded for easy identification.


Fiberglass is typically used as a backup plate for flap discs since they are rigid, sturdy, and lightweight. Due to its vibration absorbing properties and rigidity, operators will have more control over their process. Some of the leading brands of flap discs are using fiberglass backing plates.

The flaps will slowly wear away as the grain reduces when used, hence, a new layer of abrasive grains will be exposed. Over time, its effectiveness will be lessened as you keep on using it. However, you can use flap discs until such time that the cloth is already down to the resin.

What Are the Various Shapes of Flap Discs?

Conical Shaped Flap Discs

These are the best options if you want to eliminate stock in a short space of time. Conical-shaped flap discs are also great when you are working on the tip of the flaps. The limited area of contact can help in enhancing the pressure of the grinder which can increase the material removal rate. Conical discs have perfect angles, which means that hitting and damaging your workspace can be minimized.

Flat Shaped Flap Discs

On the contrary, if you need more control and a lower grinding pressure for your operations, then flat-shaped flap discs are the best choice. This is the perfect shape for blending and finishing on the outer edges and any flat surfaces. Also, you should be extra careful since the grinder could protrude further than the disc, and there is a possibility that you will hit your component with it.

What are the Different Types of Flap Disc Abrasive Grits?


Ceramic grains have a distinct microcrystalline structure that is extremely fragile at high pressure, hence, considered as self-sharpening. Since the sharp edges are constantly exposed to the surface of the workpiece, these ceramic-grained abrasives remain sharper and more efficient for a long time. The ceramic grain can do the job faster and at the same time, its heat build-up is lower. That is why these abrasives can cut at a cooler temperature, which minimizes glazing and enhances their overall efficiency. 

Zirconia Alumina

Just like ceramic, Zirconia Alumina also includes self-sharpening features. It can last longer and is excellent for heavy grinding of metals such as stainless steel and carbon steel. The crystalline structure of Zirconia is larger. It has a longer product life and is an extremely tough grain. With these features, Zirconia Alumina grain would be the best option for high-performance jobs. 

Aluminum Oxide

Typically, Aluminum Oxide is best for grinding steel however, it is also ideal for bronze and high tensile aluminum alloys. Aluminum Oxide is a blocky, fragile grain that is produced in different qualities. Its friability will likely depend on the carbon content and purity of the abrasive.

What Are the Uses of Coarse Gritted Flap Discs?

A coarse gritted flap disc is appropriate to use when the final surface finish needs to be very refined or when quick stock removal is needed, or if the client wants to get the job done quickly and does not care about the finish. Generally, the coarser the grit, the faster the rate of material removal. However, it will depend on the type of material. Also, the scratches left behind might be extremely deep to blend out.

This can be clearly seen when you compare the finishing processes on stainless steel and carbon steel. You can easily get tempted to use the coarser grains; however, this can prolong and impede your finishing options at a later phase. Coarse grits are also an excellent option for soft materials including aluminum and soft steel.

When is the Best Time to Use Fine Gritted Flap Discs?

Fine grits are the perfect option when the project requires a more refined and blended finish. Typically, they are used at the later phases of the grinding process for cleaning up deeper scratches brought about by the coarse grain during stock removal.

For instance, stainless steel generally needs additional surface finishing processes due to the properties that each transmits to the material. A highly refined finish is popularly used for decorative purposes while the number 4 finish is commonly used for commercial handrails since it features anti-bacterial and anti-fingerprint properties.

After using a grinding wheel or a coarser-grained flap disc during the initial stock removal, the scratch will not look nice on a stainless steel surface. By using increasingly finer grits, you can blend this out and obtain more refined surfaces. Finer grits tend to be more efficient on smaller areas and more appropriate for harder and more fragile materials.

When Are Flap Discs Used?

Flap discs are very versatile. It comes in a wide array of grit sizes and abrasive grains for catering to the varied requirements of customers. They are the perfect option for various stages and processes used in metal fabrication, from smoothing out surface imperfections to stock removal and deburring.

Grinding Wheels Vs. Flap Discs 

So why should you select flap discs over grinding wheels? A grinding wheel is just like a flap disc since they are also very versatile and appropriate to use on different varieties of metal fabrication applications. Grinding wheels are an excellent choice for quick stock removal, especially when surface finish is not a major concern and there are fewer steps involved in grinding.

One good example is when the weld seam is removed from carbon steel. Since the surface is commonly just painted, there is no greater need for an extremely refined or blended finish afterward. During this situation, a grinding wheel will provide you with the best value. Grinding wheels are great, however, flap discs have their own key advantages as well. 

Less re-work is needed since a flap disc offers more control for stock removal. Most often, they are lighter and offer cooler cutting with reduced glazing. This means that there are lesser chances of any re-work to be done.

This also provides a smoother finish without any gouging. Grinding wheels are very aggressive and tend to gouge the surface, leaving behind an extremely rough finish, especially if the operator is less experienced. On the other hand, the abrasives in flap discs are either made of polyester or cloth which conforms to the disc and minimizes the possibility of any damage being done to the workpiece. At the same time, the material is removed effectively.

Fewer vibrations are observed when grinding since the flap discs are more flexible and less rigid compared to their grinding wheel counterpart. Aside from making the operator feel comfortable, it also makes less noise.

For your abrasive needs, you can get them at Sparks and Arcs. We provide a wide variety of grinding wheels, flap discs, angle grinders, and so much more! For more information, just call us at 877-95-SPARK (877-957-7275) or send us an email at

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