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Home / How to Select the Right Flap Disc

How to Select the Right Flap Disc

With all the benefits afforded by flap discs, it is important to know how to select the right one by understanding all the variables and how they apply to your metal fabricating application. Here are the five variables that will help you pick the correct one.

Chart 1
From an operator’s viewpoint, flap discs are preferred for several reasons. The discs are lighter weight, easier-to-control and have less downtime for product changes. Less vibration and resulting fatigue, as well as reduced noise, are also favored by operators. With all the benefits afforded by flap discs, it is important to know how to select the right one by understanding all the variables and how they apply to your metal fabricating application.
Flap discs are used almost exclusively on right angle grinders and are designed with a hub that allows work to be done on the face (flaps). The flaps can be applied to the work at an angle or flat.
Figure 1. Type 29 Conical flap discs are the best choice for aggressive stock removal. They have angled flaps for use on both contoured and edge work. Their angle provides greater surface contact for stock removal on flat surfaces. They are the best choice when speed and stock removal are primary considerations.
Figure 2. Type 27 Flat flap discs are the best choice for finishing. Flat flap discs are used primarily on flat surfaces. They are the best choice for blending and smooth finishing. 
Standard Density flaps are excellent for heavy-duty applications and rapid stock removal. 
High Density flaps are ideal when working on uneven or curved surfaces, as well as finer grit blending.
Ceramic Alumina is a grain micro that fractures to allow a continuous supply of the sharpest cutting edges. This provides the fastest cut and best utilization of the entire grain for the longest life, especially on stainless or high alloy materials.
Zirconia Alumina is an excellent blend of zirconia and aluminum oxide grain which provides a very good cut rate to cost ratio. This is a very good choice on carbon/mild steel applications.
Zirconia Alumina is an excellent blend of zirconia and aluminum oxide grain which provides a very good cut rate to cost ratio. This is a very good choice on carbon/mild steel applications.
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Over the last decade, flap discs have been the fastest growing abrasives category in metal fabrication. From a product performance standpoint, flap discs offer fast stock removal and provide grinding, blending and finishing with one product, for a lower total cost. Flap discs feature cooler cutting with less gouging and burning.

From an operator’s viewpoint, flap discs are preferred for several reasons. The discs are lighter weight, easier-to-control and have less downtime for product changes. Less vibration and resulting fatigue, as well as reduced noise, are also favored by operators. With all the benefits afforded by flap discs, it is important to know how to select the right one by understanding all the variables and how they apply to your metal fabricating application.

FLAP DISC SHAPE
Because flap discs are used almost exclusively on right angle grinders, they are designed with a hub that allows work to be done on the face (flaps). The flaps can be applied to the work at an angle or flat. Picking the right flap disc shape, conical shape (Type 29) or a flat shape (Type 27) provides different performance features. The diagrams in Figure 1 and Figure 2 (to the right) give the features and benefits of each.

Type 29 Conical flap discs are the best choice for aggressive stock removal. Conical flap discs have angled flaps and may be used on both contoured and edge work. Their angle provides greater surface contact for stock removal on flat surfaces. They are the best choice when speed and stock removal are primary considerations.

Type 27 Flat flap discs are the best choice for finishing. Flat flap discs are used primarily on flat surfaces. They are the best choice for blending and smooth finishing.

FLAP DISC BACKING PLATE MATERIAL
The second major question is what type of backing plate you should use. All flap discs are a combination of abrasive flaps adhered to a rigid backing plate. It is the backing plate that provides stability during operation. There are three different material types:

  • Fiberglass backing plates help to absorb vibration and are consumed during use, with no smearing. Fiberglass is the most popular material because of its high strength and light weight.
  • Plastic backing plates are becoming more popular due to some conformability as well as being trimmable, which allows more use of the flaps, especially for blending and finishing. (Please click here to watch a video on how to trim plastic backing plates)
  • Aluminum backing plates are the least popular, but are good in applications demanding extra high strength and rigid support. While not consumable during use, an aluminum plate can be recycled.

ABRASIVE FLAP DENSITIES
The quantity, angle and spacing of the flaps on the backing plate can vary substantially. This is referred to as the density of the flaps. It is important to match the flap density below with your application, if possible, to achieve the best results. Standard Density flaps are excellent for heavy-duty applications and rapid stock removal. High Density flaps are ideal when working on uneven or curved surfaces, as well as finer grit blending.

ABRASIVE GRIT
Probably the most important criteria are the type of abrasive on the flap and the appropriate grit size. For metalworking, there are three primary abrasive types:

Ceramic Alumina – the latest innovation in abrasives, this grain micro fractures to allow a continuous supply of the sharpest cutting edges. This provides the fastest cut as well as the best utilization of the entire grain for the longest life, especially on stainless or high alloy materials.

Zirconia Alumina – an excellent blend of zirconia and aluminum oxide grain which provides a very good cut rate to cost ratio. This is a very good choice on carbon/mild steel applications.

Aluminum Oxide – the original metalworking abrasive, this product is recommended for smaller jobs where a consistent, low cost product is needed.

GRIT SIZE
Grit size is the final component you need to select to match your application. The grit recommendation chart shown in Chart 1 can assist you in selecting how coarse or fine you should go.

If you have not tried flap discs yet, we recommend you do, as they are a versatile solution to most metal fabrication applications. Understanding the five variables will help you pick the correct one. Most manufacturers offer a broad stock line of 4 in to 7 in to fit all popular right angle grinders. Some also offer custom manufacturing of flap discs to meet specialized or high-production applications. Be sure you consult your sales representative to help understand their total line to provide you with the best grinding, blending and finishing solution for your metal fabrication application.

13 Comments

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  • Garfiun wrote:

    After a few searches on google about what types of flap discs to use, this is the most informative and easy to understand. My application is for automotive use.

    • Mike wrote:

      Was wondering if these things are any good for body work on a car?

  • Byron wrote:

    If I have a 3 inch, aluminum oxide, 80 grain flap wheel on power drill, will that one wheel be able to suffice the polishing of the interior of a brand new 55 gallon drum? And will that one wheel keep it’s integrity for consistent polishing throughout this task? Or will I need more than 1 flap wheel for task? Please note, there is no rust, and the surface to be polished is clean and free of contaminants as well as very smooth….it’s just sheet metal…..thanks.

    • Jim Darocha wrote:

      Byron,

      Flap wheels are designed to allow the backing on the outer edge of the wheel to wear away as the abrasive grain on that area of the product becomes used. This causes new grain to be exposed and is what gives the wheel the characteristic of providing a more consistent finish and uniform cut rate than other types of conventional abrasives. The answer to your question will depend on several factors; the design of the flap wheel, the tool you are using, and the condition of the incoming material.

      1. Design of the flap wheel: Flap wheels can be made with a few different types of abrasive backings. Softer backings (J or X-weight) allow for more flexibility while heavier backings (Y-wt) create a more aggressive and longer lasting product. The spacing/density of the flaps will also have an impact on the life of the abrasive. Spreading the workload between a fewer number of flaps will cause product life to suffer. Increasing the width of the flap wheel will also help to improve product life.

      2. Tool you are using: Flap wheels should be run at the RPM they are rated for to ensure maximum performance.
       
      3. Condition of the incoming material: If the work piece has blemishes then additional pressure will usually need to be applied to remove those imperfections or a more aggressive product will need to be used. Since your drum is free of blemishes, smooth light-to-medium pressure is most likely all that will need to be applied. In this case, it will be important to pay attention to the condition of the outer edges of the flaps. If the outer edge of the flaps become loaded and the surface finish changes, it may be helpful to dress the edge of the wheel to expose new grain. This can be done by using the wheel on a smaller piece of scrap metal to increase the unit pressure and break the backing on the edge of the wheel down.

      It may also be beneficial to utilize a larger 4” or 5” diameter wheel for this application.  As the wheel decreases in diameter, clearance could become an issue bringing your hand very close to the inside of the drum. Always ensure optimum safety. 

      Jim Darocha 

  • Ivan wrote:

    Hi David, the size of my bench grinder is 6″. So I bought a 6″ flapper wheel. I removed the cover then took the old stone wheel off, replaced it with the flapper, then replaced the cover. When I turned on the grinder, the flapper expanded and rubbed the inside of the cover. So I left the cover off.
    1) was I supposed to buy a smaller flapper wheel to fit in my 6″ grinder?
    2) is it safe to use with the cover off?

    • Mike Riley wrote:

      Ivan, please contact Ethan Weikleenget, Sr. Product Safety Engineer, Saint-Gobain Abrasives, 508-795-2690, ethan.weikleenget@saint-gobain.com, for answers to your questions. Ethan will be able to help you. Thank you. Mike  

  • Allen Williams wrote:

    I don’t see the figures or chart except for a few thumbnails at the top of the article. I’m using Firefox; should I try another browser?

  • Allen Williams wrote:

    Never mind. Found ’em in IE.

  • Apurva Bhatt wrote:

    Sir,
    For 304 304l, 316 316l, and duplex 32101 stainless steel tubes and pipes, what are the best flap discs and grit in 4 in discs? Please advise. Thank you.

  • Joel Choquette wrote:

    Hi David;
    With cost for a 4.5 in disc ranging from $3 to $12.00 and the difference in shapes, I can now understand why this is. Your article was very helpful. Thank you.

  • Pat Maundrell wrote:

    I just bought my first Angle Grinder, a Milwaukee Model 6142-30. I plan on using it in Grinding and Cut-off operations. I realize I need different Safety Guards relative to the Wheels I am using, i.e. Type 27 & Type 1. However, I also plan to on using a Flap Wheel, Type 29 for grinding /polishing, but I am haven’t been able to find any special instructions pertaining to what Type Guard to use with a Flap Wheel. I assume the Type 27 Guard will be the choice.
    Additionally, what are your thoughts on using a Type 1 guard while using a Type 27 Grinding Wheel? It seems to me that the Type 1 guard would add greater protection over a type 27 gaurd.

  • donald lutz wrote:

    i need to sharpen teeth on a forestry they are hardened to rockwell 57 i use a gas powered 7″ angle grinder

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