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Secrets to Achieving Seamless Welds with Flap Discs

Secrets to Achieving Seamless Welds with Flap Discs

When the welding is finished, you want your weld to appear to be barely there. Those photos of the completed welds have been posted on social media. And you want yours to resemble theirs exactly. But how exactly do they do that? Naturally, they make a strong weld that looks good. However, the welding preparation. Cleaning up after the welding.

Additionally, smoothness is crucial. It would help if you used a flap disc of the appropriate grit size. How, then, do you choose the proper grit size for welding?

Continue reading to learn more.


The flap disc's rough surface is known as grit. It is the area of the flap disc that completely abrades the welded metal. And you'll see that there are various grit sizes when you go to buy your flap discs. What does all of this mean, then?

You can determine the size of the particles on the flap disc's surface by looking at the grit size. The most popular grit sizes are 24, 40, 60, 80, and 120 grit.

Larger grit sizes, such as 150 grits and above, are available. It can be used for extremely precise and professional smoothing operations. You'll observe that grit is available in a variety of sizes. Different materials are used to make grit. Materials such as zirconia, aluminum oxide, and zirconia-alumina.

Some flap disc surfaces work better with aluminum or stainless steel. So, it's best to choose more than just the appropriate grit size for the task. Select the flap disc's surface grit in accordance with the metal you intend to weld on.

Additionally, keep in mind that the grit sizes with lower numbers are harsher and more aggressive on metal. The gentler grit sizes are the higher ones.


Accept that when welding, you'll require flap discs in a variety of grit sizes. Why?

You'll begin with the most fundamental metal. Or components to fix the welds. You'll also want to give yourself the best chance of a strong weld before you begin welding. Clean, smooth metal is essential for it. You can get there by using the proper grit size on your flap disc.

Start by using the coarsest grit size that is least damaging to your metal. However, it will get you the desired outcome.

Consider that you want to remove what is necessary. And depart with fine metal. For your weld, try to leave as much metal as you can. And that necessitates beginning with a coarser grain size. Say the flap disc is 60 grit.

Start slowly. You apply light pressure when using flap discs. The flap disc is supposed to perform the work for you. Nor physical force. Then, for the areas of your welding project that require it, you may always switch to a rougher grit size. If that old weld still exists, you can move up to a 40-grit flap disc. Or the rust isn't moving.



This is a fairly coarse grit size, as you'll discover. It will swiftly remove a lot of metal. Utilize heavy metals. Or metal that has significant burrs that must be smoothed down before welding. Use this grit size only when your metal needs the utmost aggression.


You employ us to access and remove old welds. Consider that you want to replace it with a brand-new weld. The edge of your metal is ground using a flap disc of 40 grit. An example would be if you were using your MIG or flux core welder at home. Not even for welding 1/4-inch welds, either.

A 40-grit flap disc can be used to bevel or chamfer the connection you intend to weld. Get ready to use your home welder several times to make multiple passes at the joint.


If your mild steel has paint or rust on it, choose 60 grit. Try this first on your thinner metals since it is kinder than a 40-grit flap disc.

Utilize it to clean your metal of any grime. You'll find that using this grain size to deburr thin metal is also a good idea. And prepare your metal's edges for welding.

Or, for thin galvanization on your steel, use a 60-grit flap disc. If you're unsure whether a 40-grit size would be too aggressive to utilize on your welding project, start with your 60-grit flap disc. If 60 grit is not nearly enough, you can easily switch to 40 grit in the future. To polish and smooth the surface of your completed weld, use 60 grit. And to cover up those sanding marks. When you began, you used a grit that was too coarse for the metal you were welding.


A soft, light flap disc. When you want to grind lightly, you can use 80 grit. Or keep it gentle with thin metal when you want a finish that looks more polished. To make your weld blend in with the metal around it, use 80 grit.


If you want a smooth surface finish, choose the 120-grit setting on your flap disc. When you want to give your metal and weld a wonderful final shine, use this flap disc.


When the mild steel is at least 1/4 inch thick, you might need a 24-grit flap disc if there is severe corrosion or rough edges to deal with. The rest of it. The numbers 40 and 60 are acceptable starting points. Clear the joint of the mill scale and prepare it for welding. For a clean finish and mix of your weld, finish with 80 grit or 120 grit.


Do you grind stainless steel with a flap disc? Yes.

Even brand-new stainless steel straight from the factory will have surface grime despite its glossy appearance. Before welding, you'll need to remove any dirt. Although stainless steel appears to be durable, it is simple to ruin its brilliant appearance. Choose the grit size based on the outcome you wish to obtain.

Start as gently as you can with the flap disc grain size. For thinner stainless steel and a superior finish, use 80 grit.

If you need to remove any existing welds, go to 60 or 40 grit. Or difficult to remove burrs. However, it is just as significant as the grit size. It would help if you chose a grit made from a substance safe for use on stainless steel. A flap disc grit surface that runs cool is what you need. Avoid leaving scorch marks on your stainless steel. Then, select the desired grit size.


Something similar to stainless steel. Aluminum seems durable. Yet, it has a melting point that is substantially lower than mild steel. So, the grit size is just as significant. You require a flap disc made of aluminum. Because an overheated flap disc surface may readily become clogged due to aluminum's lower melting point, you should search for zirconia and zirconia-alumina grit surfaces. Select a grit size of 80 or 60. And remove aluminum oxide by grinding. Within a few minutes, aluminum oxide will start to form on the aluminum's surface. As soon as your bare aluminum is exposed to air, it begins to develop. Always disc it off with a flap before welding.



In order to reduce a weld as much as feasible, grinding is the initial processing step. The difficulty of the material, the type of weld, the welder's competence, and a few other factors all affect how much effort is needed for this stage. Most of the time, a right-angle grinder is the most economically efficient tool for grinding down a weld bead.

Fiber discs, flap discs, or smaller variations of these items, utilized for greater control or to deal with smaller work envelopes, can be used as the abrasives on these tools for this application. However, flap discs differences with grinding discs. Fiber discs have a quick initial removal rate when removing extra material from flat and curved surfaces. A few pointers

  • To swiftly remove the weld and provide a surface that can be improved further, use a ceramic disc with a 60- or 80-grit rating.
  • To more quickly remove stock, use a hard backup pad.
  • To lower heat in the grind zone and prevent burn, use a product with a grinding assist.
  • Use a 10 to 15-degree approach angle to remove the weld effectively and quickly.

Flap discs have a long service life and are useful for eliminating thick weld seams and extra material:

  • A 60-grit ceramic flap disc is advised for general use.
  • The most effective option is a Type 29 conical for increased speed and stock removal.
  • A Type 27 flat is the finest option when blending and smooth cuts are necessary.

Flap discs have the following benefits over a single-layered product:

  • Up to a 20-fold increase in service life; lower labor costs due to fewer disc changes.
  • Improved finish consistency.
  • No need for a backup pad.
  • Easier to store; it does not curl.

Higher-performance ceramic grain abrasives function best when driven by an angle grinder with a power rating of over 1,200 watts, whether utilizing flap or fiber discs.


The second stage consists of erasing the first phase's scratches and establishing the final product's directional scratch pattern. During the takedown process, it is crucial to move below the circular scratch pattern the grinder produced. When attempting to achieve finer finishes, deeper grind lines may form if this pattern is not entirely erased.

To complete this stage, known as a No. 3 finish, an ordinary 100- or 120-grit abrasive belt in the part's appropriate size is used.

It is typical for the scratch depth, pattern, and direction to be homogeneous over the product's surface for applications requiring a No. 4 to No. 8 finish. Start with a medium-grit, nonwoven belt or wheel; it is customary to use an abrasive with the same linear scratch pattern as the abrasive used in the preceding phase to produce this finish.

After stripping the weld down, a rotary tool can complete the task if the final result does not require a uniform directional scratch pattern. An expensive nonwoven unified wheel or a nonwoven surface conditioning disc are the two abrasives of preference in this situation. Surface-blending discs offer lower cut rates with finer finishing capabilities and follow the curves of the surface.

Random scratch patterns can be avoided by carefully using the disc at a 10- to 15-degree angle. A coarse-grade disc can mix, preparing the surface for coatings like paint or polish.

Early on in the blending process, switching to a nonwoven product may be advantageous. To cut down on the number of distinct operations, deburring, blending, and finishing can all be done with one nonwoven product, for instance. A nonwoven product further reduces the possibility of undercutting and gouging while offering a regulated, maintained finish. The nonwoven product category also offers a cooling effect to reduce the possibility of warping or discoloration. It runs more quietly and vibrates less at the end.


Results can be improved by following a few safety guidelines and basic productivity advice:


  • Examine all the safety guidelines issued by your workplace, the government, or any other relevant authority:
  • Avoid grinding close to flammable or baggy garments.
  • Work exclusively in well-ventilated places, and set up the workspace so that sparks and other debris are directed away from you and other people.
  • Consider the project's size and shape when organizing the grinding procedures. Avoid overreaching and working off balance when handling heavy or large workpieces. To hold small workpieces in place, use a vice or clamps.
  • Keep your distance from the backup pad or rotating disc.


Follow the manufacturer's directions when mounting the disc. Never insert anything into a disc's scooped holes when using it.


Using an abrasive disc isn't difficult, but using one properly is a matter of learning numerous dos and don'ts:

  • Before commencing to grind or sand, start the tool just off the workpiece and rev it up to full operating speed.
  • Always insert the disc with a 5- to 10-degree angle to the surface of the workpiece.
  • Search for any spots on the workpiece where the disc might catch, snag, or get jammed. Work the disc gradually into the rough surface before letting the edge of the disc bite into it, as opposed to ramming it into the region. Even the hardest coated abrasive disc will break under excessive edge pressure.
  • If you need to grind a depression, molding, lip, or thick weld, start there and work your way out. Never transfer the grinder into such a contour or feature from a flat region.
  • Use only a portion of the disc's surface when removing heavy stock with a disc. The entire tool will probably shake in a harsh, jumpy manner as a result of doing so.
  • Avoid tight corners and any other areas where the disc could catch or snag while utilizing a non round disc and backup pad.
  • If the tool starts to vibrate or clatter while being used, cease it right away. Prior to moving on, identify the issue and fix it.
  • Replace the backup disc and pad if you drop the tool before moving on.
POST GRINDING: Wait until the disc has stopped rotating before putting the tool down. Avoid storing or using the tool with the disc and pad in it.
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