Flap Disc: The Complete FAQ Guide

flap disc

Do you need quality flap discs for all your industrial requirements?

Do you search for some of the best flap disc manufacturers around to supply you with top-quality tools?

Amongst sturdy and effective tools that Syndent design includes quality flap discs. Syndent flap disc offers numerous industrial functions to make your work easy.

After reading through the entire guide, we promise you to find the best flap disc for all your needs. Trust us to take you through.

What is Flap Disc?

Flap disc refers to a tool used for conforming and shaping materials. This tool actually features layers of dense sandpapers or abrasive cloth flaps to form a special tool. You can shape certain materials using flap disc to live a fine finish look on your piece of work.

Syndent flap disc has common uses in machining, welding, industrial maintenance, heavy-duty equipment, etc. They also have more uses when it comes to food production and agriculture. Flap discs provide several benefits to most manufacturing applications. They remain very much distinctive from a lineup of other surface conditioning tools including cutting.

Sometimes colloquially called flapper wheels, flap discs have a unique design that suits right-angle grinder uses. They aggressively remove heavy stock from different materials, especially metals. You can positively apply these discs for precise blending as well as finishing, based on your needs. This ideal tool offers exceptional versatility with great maneuverability.

Syndent flap disc guarantees reduced noise level operation with a low vibration working experience. They can suitably replace grinding wheels in very many special ways.

Choosing flap discs can help you do numerous tasks. They allow you to do material grinding as well as finishing efficiently while greatly saving on time. This eventually lowers manpower costs and other expenses.

Syndent flap discs operate most similarly as hard grinding wheels. However, they provide the easiest way of controlling them. Thus, you have a reduced risk of making gouges on your workpiece. Even after the abrasive area wears out, you can still use the tool because it exposes a new abrasive.

When using a flap disc for your workpiece requirements, you experience a softer touch than grinding wheels. You don’t incur risks of removing a lot of material when doing a project since they don’t provide overaggressive grinding.

When you choose a quality angle grinder flap disc, you should consider several things. This can include material, density, shape and the shape and type of abrasive grain. When grinding materials with a flap disc, you use the same power applied when using die grinder bits. The technique can sometimes differ.

What Differentiates Flap Disc From Grinding Wheels?

In our earlier statement, we outlined that flap discs refer to tools with overlapping abrasives. We glue the overlapping flaps radially on the backing plate. When you choose the right flap disc for a specific job you save on time and money. They generally have faster stock removal on different materials. You can generously use them in blending, grinding and finishing, all in one.

Flap discs can remove up to about five times of material with reduced workpiece gouging than a standard grinding wheel. For decades, flap discs have had outstanding job performance when used on high-speed angle grinders.

Further improvements on the tool through the latest technology has seen them replace standard grinding wheels. Syndent uses vastly improved raw materials to make quality flap discs appreciated in the industries.

The grain structure of the flap disc, the backings, bonding, backing plates and backings improves work efficiency. You benefit from increased blending, grinding and finishing rates with just a tenth reduced noise of famous hard wheels.

Hard wheels or grinding wheels feature abrasive grains with fiberglass layers bonded together to form a wheel shape. Here, abrasive grains represent grinding tools that can remove extra materials from your workpiece, refining and shaping it. Just like flap discs, grinding wheels can grind machine materials.

flap disc

Flap discs have high versatility features, lightweight and quite durable than angle grinder grinding wheels. Thus, flap discs have increased efficiency on work output as they extend replacement intervals.

What Makes Flap Disc Ideal Than Grinding Wheels?

The latest technology has changed the way industries use flap discs to complete different tasks on most materials. Flap discs have incredible versatility and come in different abrasive grit and grain sizes that cater for all your requirements. Essentially, flap discs represent special abrasives used in metal fabrication. They remain the best choice tool used in various industrial applications.

Although grinding wheels offer incredible versatile uses in metal fabrications, it doesn’t leave fine surface finish like a flap disc. Grinding wheel suits applications that necessarily require surface finishing and you don’t need extra steps that proceed to grind. Such a perfect example includes clearing a weld from carbon steel. Since the surface has only paint, grinding wheels can suit such function. You don’t require a highly refined or blended finish on the materials afterwards.

However great grinding wheels have to offer, flap discs have better advantages including the following:

You don’t need extra Re-work

With Syndent flap disc you greatly benefit from controlled stock removal on given materials. Lighter in nature, they provide precise and cooler cutting with less glazing. This indeed reduces the high need for re-working experienced with grinding wheels.

Smoother finish without gouging effects on materials

With grinding wheels, you may experience extreme aggressiveness when removing stock. Furthermore, they have high tendencies of gouging material surfaces which leaves a rough finish. This comes out when used with an inexperienced user.

When you use a flap disc in such instances, you won’t incur gouging on specific materials but a smoother finish. The abrasive flaps feature special polyester or cloth that provides lots of comfort to a disc. This can hugely minimize high chances of damaging your workpiece but fluently and smoothly remove a good amount of material.

High-degree minimized vibrations

The flap disc has reduced rigidness with high flexibilities than a grinding wheel. This can imply fewer vibrations generated while grinding. Besides making your grinding experience much easier and comfortable, you have significant noise reduction with Syndent flap disc.

What Popular Bonding/Backing Materials Do Flap Discs Have?

Backing and bonding materials popularly used in flap disc include the polyester cloth or poly-cotton cloth. The ideal cloth has abrasive grains coated on them. The abrasive cloth used to come in smaller specially designed strips that appear in layers, overlapping each other. This forms a flap disc hence its name. Rigid back plating can provide greater stability as well as support.

Flap disc designed with poly-cotton provides great grain retention and remains flexible than the polyester backing. Although less flexible, polyester cloth provides better durability, strength and performance life.

What Types of Flap Discs Do We Have?

The most popular types of flap discs appear to include the flat disc and the conical disc.

Flat flap disc

Also called type 27 flap discs, they provide the best material grinding when dealing with shallower angles. This can range from 0 to 15 degrees. They provide optimal functions of smooth finishing with perfect blending on most flat surfaces. Furthermore, flat discs can perfectly manage slight contours.

Conical flap discs

As called type 29 flap discs, conical flap discs have a grinding surface that appears like a saucer. They don’t look like ordinary straight discs and provides perfect grinds at angles ranging from 15 to 35 degrees. They allow you have aggressive removal of stock because of maximized surface contact, especially on flat surfaces.

Useful note: For the initial high-volume performances, use the conical flap disc. And for precise refinements, switch to a flat flap disc.

Do Flap Discs Have Special Styles and Shapes?


You can find few flap disc shape and style specialties. These may include:

Trimmable flap Discs

Trimmable discs have different appearances compared to other types. They feature special composite backing you can easily trim, increasing flap overhang. When used with the right intention, these ideal discs can offer high versatility and flexibility in areas hard to reach. This can include irregular shapes as well as fillet welds. The backings can also protect from making unwanted marking on your workpiece.

Aluminum-backed flap discs

Flap discs that have aluminum backs feature a very sturdy and permanent aluminum backing. With such backing, you benefit from rigorous support in heavy-duty and high-stress applications like pipeline fabrication.

Mini flap discs

Just like the name sounds, mini flap discs look significantly smaller compared to standard counterparts. They have measurements of between 2 and 3’’ in diameter. Due to the compact size, mini flap discs ideally suit grinding operations in hard-to-reach positions on your workpiece.

Using the smallest 2-inch mini flap disc you can fulfil project demands perfectly better than a blending disc. These discs feature composite backing which gives standard support to handle a range of material applications.

Angled flap discs

These type of discs have a special design of curved flaps, wrapping the backing plate edges. This can facilitate substantial flap-to-metal contact which eventually enhances operator control. Thus, you achieve broad grinding angles.

Curved flaps provide contouring capabilities to the ideal angled flap disc that can easily suit fillet welds. Therefore, you can access those tight areas other flap discs can’t easily reach. They have hardy grinding performance when dealing with flat surfaces.

Flap discs feature several useful sizes that range from 4 to 7 inches in diameter not forgetting mini discs too. Syndent smaller flap discs have a perfect suit with die grinders for smoother grinding with enhanced comfortability. This provides formidable performance in tight places as they rotate fast for a faster cutting rate.

Larger flap discs have slow rotation. Larger diameter wheels have greater abrasive and with the right maintenance, the large size covers larger areas and lasts longer. They also provide higher rates of removing stock.

Syndent flap disc shapes have different width of any single flap. Stipulated industrial standard of flap disc flaps falls around 25ml while some have 30ml flaps instead.

Useful note: Larger flaps provide a larger surface area with applications that need aggressive and high-volume grinding.

Which Materials Can You Find Flap Discs In?

Syndent flap discs appear in different abrasive grit material where ceramic outshines the rest. The following represents some of the common types you can find.


flap disc

When in search of maximum performing flap disc, ceramic can perfectly fulfil your material demands. When grinding, ceramic flap disc micro-fracture and constantly expose the sharp edges while maintaining the highest cutting rate. Thus, the ideal Syndent flap disc lasts longer than any of its counterpart.

Ceramic ideally suits workpieces obtained from tool steel, standard steel, titanium, armored steel, Inconel, aluminum, stainless steel, etc. It also has exceptional performance when applied on hard-to-grind metals.

With an additional topcoat, Syndent ceramic alumina can provide a fast cut-rate, grinding at a cooler temperature. This greatly helps in protecting valuable components with heat sensitivity hence reduced heat discoloration on your workpiece.

A top-coated ceramic flap disc can as well prevent loading. Syndent ceramic flap disc option with a top coating is contaminant-free that promises astounding performance, especially on steel workpiece.

Important note: Loading simply refers to the accumulated workpiece material bits that appear on a flap disc.

Zirconia alumina

flap disc

Like ceramic material, Zirconia Alumina featured self-sharpening characteristics. This implies the flap disc that has such elements have a long life with improved grinding performance on metals. Zirconia Alumina flap disc therefore can heavily grind metals like stainless steel, structural steel, cast iron, carbon steel, etc.

Zirconia comprises of larger crystalline structure that produces tough grain for wonderful product life. Such exemplary features make the Zirconia alumina flap disc a good choice for tasks that need high-performing tools.

If you want 100% Zirconia alumina, Syndent provides you with an excellent option. It has self-sharpening features and holds up professionally well even with high pressures and temperatures.

Aluminum Oxide

Flap disc designed from aluminum oxide have durable grain, are hard with a powerful initial cut-rate. You benefit from fast stock removal with consistent performance. Generally, aluminum oxide flap discs grind steel but can apply on specific high tensile aluminum as well as bronze alloys.

Syndent manufactures aluminum oxide flap discs in various qualities with blocky and friable grain. Abrasive friability depends on both carbon content and purity. Syndent designs flap discs with aluminum oxide grain.

The ideal flap disc can provide all-purpose functions. Since it lacks self-sharpening features, the aluminum oxide flap disc single crystals dull during a period of use. Otherwise, Syndent aluminum oxide flap discs give a combination of great performance with value.

Do Flap Discs Come in Grit Sizes?


Grit size means an abrasive grade of the material and you can choose appropriately based on applications.

Syndent designs flap discs in grit sizes of coarse, medium and fine. The higher-grit number means smaller abrasive grain, hence, a finer abrasive flap disc. Coarser grit size can perfectly grind applications and remove heavy stock. Choosing a flap disc that has finer or medium grit size can provide superb blending, finishing or deburring applications.

As earlier indicated, flap disc sizes range between 2 inches and 7 inches based on material application.

Flap discs in smaller sizes of between 2 and 3 inches can outperform a standard quick-change disc. It can give 15 times more uses which significantly reduces the number of item changeovers. This increases output productivity by a big margin and eventually lowers the entire cost of the application.

Also, they allow easy maneuverability in tight areas.  The design helps in preventing the disc against ‘’walking’’ on the material.

Does Flap Disc Require a Special Application Technique?

Not a very special but a proper technique. This helps to maximize the effectiveness of the flap disc and improve its longevity. Exerting excessive pressure while grinding materials with a flap disc usually causes gouging or premature wear. Also, it can result in discoloration, heat buildup and undercutting.

In case your workpiece demands extra push on the flap disc, switch to a coarser one or another disc. Insisting on using too much extra pressure may severely damage your workpiece with safety and health issues a big concern.

Allow the flap disc to freely work on specified materials which greatly reduces chances of stress-related injuries.

When using Syndent premium grinding grains such as ceramic alumina, use a rotary tool that has enough power. This ensures you have the constant rotational speed for outstanding results on your project. Using an underpowered die grinder can easily bog down when exposed to excessive pressure. As a result, you have the minimal ability of the grains to fracture as well as self-sharpen.

Syndent flap discs have special designs in such a way that their full-width flap can provide optimum performance. Grinding at a steep angle subjects the flap disc to harder work because it doesn’t use a full cloth width. This greatly reduces the flap disc life as the flap experiences increased stress.

What Backing Plates For Flap Discs Do We Have?

Syndent flap disc backing plates typically appear in three popular types: metal, fiberglass and nylon/plastic.

Fiberglass backing plates

Also called phenolic, fiberglass is quite popular and commonly used raw material in making flap disc backup plate. Fiberglass is lightweight, strong and very rigid. The vibration absorption and rigidity properties of this material help you remain in great control during different processes.

As the flaps wear out gradually when the grain diminishes after long use, it exposes a new abrasive grains layer. The effectiveness of fiberglass backing plates can decrease after several uses. But you can still use the flap disc until you see the resin. However, fiberglass doesn’t contaminate the surface of your workpiece. It forms a powerful bond with the adhesives but requires a backing flange.

Plastic/Nylon backing plates

Sometimes called trimmable backing plates, this popular choice features low cost and flexibility. Flap disc manufacturers commonly use nylon for the backing plates because you can easily trim them during operation. This can sometimes increase the disc operating durability up to 65%.

Recommended trimming length vary from one manufacturer to another but the preferred length features 3/8-inch. Some plastic backing plates can shutter, therefore you need to confirm that the one you have indicates trimmable. Plastic comes in a variety of colors and is common in European countries.

Metal backing plates

The most common metal here features aluminum which offers the greatest support and stability of the two options. However, aluminum appears a bit expensive compared to fiberglass and plastic. Although stronger with good support and stability, once revealed when the material wears out, it can gouge your workpiece. Unlike the two mentioned above, a metal backing plate doesn’t need a backing flange.

What Determines the Abrasive Grit Size You Choose for Your Application?

Flap disc manufacturers design them in assorted sizes, just like the sandpaper grains. Flap disc grains appear in ranges of between 36 and 120. Smaller numbers indicate larger and coarser grit. Larger numbers indicate smaller and finer grit.

Generally, you need coarser grit to shape and remove stock. You need finer grit to make refinements like doing repairs, blending or finishing.

The breakdown below clearly shows how the numbers signify the performance of Syndent flap disc:

  • Removing heavy stock: You require larger abrasive grit that lies between the 36 and 40 range. This facilitates all heavy-duty tasks including the removal of heavy stock from your workpiece.
  • Edge beveling and Chamfering: Apply larger abrasive grit with slight advancement of within 36 and 60 range. This perfectly facilitates edge work like edge beveling as well as chamfering.
  • Blending and weld grinding: Requires abrasive grit with range sizes of about 40 and 60. This can suit applications such as blending and weld grinding.
  • Deflashing and deburring: A suitable abrasive grit of 60 is ideal in deflashing and deburring.
  • Removal of rust and blending: You need a more expansive abrasive grit grain which ranges from 60 to 80. This provides optimal performance for finer work including removing rust and blending.
  • Cleaning and finishing: Requires finer abrasive grit with ranging sizes of between 80 and 120. It well suits very delicate refining tasks like finishing and cleaning.

Which Common Industries Use Flap Discs?

So far throughout our description, we have covered how different grain sizes can enhance the performance of flap disc. Depending on the material requirements, you have the freedom to choose an abrasive grit grain that suits the application.

Let’s now see how you can suitably use Syndent flap discs in various industries:


For construction applications, industries can use 5-inch or 6-inch Syndent flap discs because of their lightweight and portability. A 5-inch or 6-inch Syndent flap disc can provide the best performance needed in a construction job site.

Metal fabrication

Syndent flap discs can provide indispensable functions in general metal fabrication. They have high adaptability and versatility to provide various grinding applications. This includes stock removal, deburring, cleaning and finishing. Thus, Syndent flap discs remain superior tools you can use on various metal workpieces.

Pipeline development

Syndent quality flap discs play a vital role in the pipeline industry by providing sturdy support in development. You can use our discs to remove heavy pitting in preparation for welding. Designed with aluminum backing plates that protect the disc from reaching the bevel while grinding.


Different industries such as shipbuilding or trailer fabrication use aluminum as a choice metal. Aluminum usually tends to load because of its softness. Therefore you need a flap disc that has a topcoat that greatly prevents gumming up. Other than Syndent ceramic, we offer Syndent aluminum that has a topcoat. Syndent aluminum provides a special combined flap design for guaranteed high performance to grind aluminum at an affordable cost.

How do You Differentiate Different Densities of Flap Discs?

Flap discs come in different densities determined by the quantity and quality of abrasive cloth element. We have standard flap discs and high-density flap discs. Syndent high-density flap discs have a good amount of abrasive cloth material compared to a standard one.

Thus, the high-density flap disc appears thicker with more forgiveness. Based on high density, they easily adapt to any irregular surface which a standard flap disc can’t do. With a high-density flap disc, you have greater control of the tool. You also have better performance even on non-standard shapes or materials.

You can either have type 27 or type 29.

Type 27: This kind has a similar straight profile common with flat flap discs with extra thickness. You can confidently use them to effectively grind materials at angles of 0 to 15 degrees. Flap discs of such nature easily conform to surfaces of all nature.

Syndent 27 high-density flap disc can give you smooth grinding, blending or finishing on irregular and flat surfaces.

Type 29: Syndent designs type 29 high-density flap discs that have angled profile, similar to conical flap discs. You can accurately grind angles that lie within 15 and 35 degrees. Featuring an angled design and high density, you can aggressively remove stock with easy conformity to irregular surfaces.

In general, standard density flap discs provide excellent performance in the aggressive removal of heavy stock. They suit the most demanding industrial applications. High-density flap discs ideally suit functions on materials with uneven or curved surfaces. You can comfortably use them well in blending as well as finishing and not heavy stock removal.

Can a Flap Disc Grind Aluminum?

Most definitely.

Flap discs appear as the best tools you can use for grinding aluminum. By design, Syndent flap discs can perfectly grind most metal surfaces at relatively reduced temperatures compared to other discs.

Aluminum has the lowest melting temperature which melts easily. To remove stock easily, use Syndent T29 conical flap disc. Apply the same at a 15-degree angle for befitting surface contact.

For surface-cleaning or smooth finishing, the T27 flat disc, parallel to a work area can have great performance.

Can a Flap Disc Grind Wood?


We have special Syndent flap discs designed for outstanding performance on wood. Syndent flap discs for wood have the same design as that used on metal. The aluminum oxide grit can provide an exemplary function for any wood application.

With wood, use the flap disc with your angle die grinder.  This is similar way you apply with a grinding wheel. To reduce deep scratches, begin with heavy grit as you work through to lighter grits to achieve the final finish. Use between 120 and 220 grit sizes if you want furniture-grade surfaces.

Which Flap Disc Should I Use For Paint Removal?

Sometimes metals lose their paint and begin to rust. Cars also can lose their original attractive paint with time which you need to remove and apply a new one. Syndent non-woven flap discs perfectly remove rust and paint from metals. Also, flap discs that have aluminum oxide can sufficiently remove paint and rust.

Do We Have Flap Discs Suitable for Concrete?

For the case of concrete applications, you need flap discs made from diamond or silicon carbide. Since diamond and silicon carbide have hard features than any other material in the world, they can suit concrete applications. Such hard discs allow applications on concrete with low pressure.

Diamond or silicon carbide designed flap discs consists of rigid backings. This gives them high versatility features to work on several other surfaces. You can grind granite, marble, engineered stone or ceramics.

What Should You Consider Before You Start Using a Flap Disc?

To use a flap disc well, you need a bit of knowledge of handling it and some safety measures. Always consider the following:

  • Ensure you understand your flap disc well
  • Go through the user’s manual thoroughly and understand the instructions
  • Use proper safety gear to protect yourself from injuries caused by the tool and your workpiece
  • Ensure you work in a safe environment
  • Know the purpose of the tool you want to use

Partnering with Syndent you benefit more than just the initial purchase. We design safety and quality flap discs acceptable in the industry. Amongst our other products include carbide burrsrotary filesdie grinder bits, etc.

For information or enquiries about Syndent quality flap disc, contact us.


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