5 Best Flap Discs for Cleaning and Prepping Mild Steel

By Ben Norton / April 15, 2019
Best Flap Discs Title Image

You plan to weld with a MIG welder or flux core welder ​and you know to get the best results out of your welding efforts that the light mill scale, rust or paint on your steel has got to come off.

Not only that, but you know that when your done welding you're also going to need to get that spatter off. Maybe take off some stubborn flux core welding slag, or smooth off that welding bead profile.

Flap discs are chosen when using a grinding wheel disc would be too aggressive. When you risk gouging out you're mild steel or your looking for a disc to use when you've done the hard stuff with a grinder and need a smoother rub down.

You have your grinder, you may even have ran through a number of flap discs and was disappointed. Now you want to look for and buy the best flap disc.

Let me see if I can help.

​These are the two flap discs that came out on top in my research. And I have more detail on them below. But hold on ...

​There were runners up. Runners up that in my assessment are worth a look at. Depending on your needs and budget, here are the best along with the 3 runner up flap discs.

The Top 5 Best Flap Discs

​Top 3 Type 27 Flat Flap Disc Picks

​Flap Disc

​Price Est./Our Rating

​On Amazon

​1. Winner

Walter Technologies 15W454 FlexSteel Flap Disc

$$$  /  4.8/5

2. Runner Up

Weiler 51108 Tiger Paw High Performance Flap Disc

$$  /  4.6/5

​3. Worth a Look

​Kseibi Aluminum Oxide Flap Disc

$  /  ​4.5/5

​Top 2 Type 29 Conical Flap Disc Pick

​Flap Disc

​Price Est./Our Rating

​On Amazon

​1. Walter Technologies ​15R454 Enduro-Flex Flap Disc

​$$$   /  4.9/5

2. Runner Up

​​Benchmark Abrasives ​High Density Jumbo Zirconia Flap Disc

​$$  /  4.7/5

Why is a Better Flap Disc Important?

When you're preparing to weld, good clean steel is the best place to start, whether you are a novice welder laying down your first bead or much more experienced.

You may need to bevel your weld joint if your steel is a thick gauge for your welder to deal with and you have a 110 or 115 volts MIG or flux core welder. A flap disc can help you prepare that joint.

And when you're finished welding the clean up will ready your steel for the next weld pass. Or if painting or applying rust protection a flap disc can get you a surface you can apply on.

The Crucial Need to Knows When Choosing The Best Flap Disc For You

And yes the best disc for you and your project may change based on the size of the piece, your budget and who is going to care about how it looks when you're done.

Flex Steel Deburring Mild Steel

Flex Steel Deburring Mild Steel

Flap Disc 101's

1. The higher the grit number the softer the flap disc is on your mild steel.

2. A 40 Grit is the highest grit number and is more aggressive. This grit level on a flap disc is used for weld removal, removing galvanization or for getting rid of heavier mill scale.

If you're dealing with really heavy mill scale you may want to take a look at my article "Mill Scale Removal Before Welding Mild Steel - 3 Ways" before you read further.

3. A 60 grit flap disc is a general purpose grade. Widely used for preparing mild steel by grinding off rust, mill scale and paint. Also de-burring steel and rounding and beveling edges. And it is used for medium grinding off of your weld bead once you have finished welding as well as removing weld spatter.

4. Flap discs are the best choice when readying thin steel gauges for welding. Where grinding aggressively will remove too much metal. This is particularly true for those of you welding auto body parts where thin gauges of mild steel are used.

5. The best flap discs spin up and work cooler on the steel and the result is less gouging of your metal.

6. All the flap discs chosen for the best of list are 4 1/2 inch diameter, made for a 4 1/2 inch angle grinder. Many are available in larger sizes if you want to go through to Amazon and check.

A Quick Word on Flap Disc Types

Type 27 flap discs are flat. Well reasonably flat in that they can have a 5 to 15 degree grinding angle. They are best used for preparing your mild steel for weldng, cleaning off dirt and mill scale. For the finishing off of your project piece by blending your weld into the surrounding metal and for making your steel look good before painting.

One more thing, because they are flat, type 27 flap discs are perfect for getting into those tight corners and for smoothing down the surface of those rough filet welds. And use for corners where you don't have much space to work in.

A type 29 flap disc has a more conical shape, with a 15 to 35 degree angle on the grinding face. They also have a depressed center.  They too can prepare your steel, clearing it of mill scale and rust.

Type 29 flap discs are ideal when you want more aggressive grinding and you want to work at speed. They are best used on steels with contours, because their conical shape makes it easier for these flap discs to follow the curves.

A good example where you would use a type 29 flap disc is for smoothing down a weld on the contours of a car or truck body. They are also great for using on the edges of mild steel.

Now let me take you through the flap discs I have selected as the best in more detail. Feel free to click on the links I have provided below to go check out these flap discs on Amazon.

The Winner of the Type 27 List

FlexSteel

Overview

The Flex Steel is available in 40 grit, 60 grit, 80 grit and 120 grit.

This flap disc is manufactured for mild steels and low carbon steels only and has a Zirconia Alumina surface, which is a high grade surface for a flap disc.

As a flat flap disc use it to prepare your steel for welding. Take off that mill scale before MIG or flux core welding. Remove rust. Even out your weld beads and remove spatter.

This flap disc has a 7/8th inch arbor hole.

The maximum supported rotation speed is 13,300 rpm. Comes in a pack of 10 flap discs.

Reasons to Buy

As the best it is proven itself in the field as a flap disc that lasts a long time with out clogging up.

The Zirconia Alumina surface is made to self sharpen as you use the flaps.

The flaps work into the metal with minimal pressure. A real plus is that the backing plate is designed to be trimmed down to extend the life of the Walter FlexSteel flap disc.

The FlexSteel flap disc can be put on with no tools so is time saving.

Reasons Not to Buy

These flap discs are pricey and depending on your budget you may find they are just out of your reach.

Some would prefer to go with a non premium product because they don't need the finish these flap discs give or prefer to use multiple flap discs from more budget brands.

To get the longest life out of these discs you will need to trim them down, if you don't you're really not getting your money's worth.

In Conclusion

The FlexSteel won out because it performs when the going is tough. Users of this disc love the way it just goes on and on when others have already clogged up.

There is a price you pay for the best.

YouTube Video on the Walter Surface Technologies FlexSteel

Have a look at this promotional 53 second video that takes you through the different uses this high performing flap disc is capable of. Its worth a look.

FlexSteel

​Video Credit: Walter Surface Technologies

Runner Up on the Type 27 Best Flap Disc List

Tiger Paw Flap Disc

Overview

The Tiger Paw is available in 36 Grit, 40 Grit and 60 Grit

Has a Zirconia Alumina surface for use on mild steel and low carbon steels.

Use this flap disc to make ready your steel surfaces for your MIG or flux core welding, smooth down that spatter and slag.

The Phenolic backing on the flap disc prevents the marking of your project piece and allows you to use the flap disc down to the backing,

This flap disc is designed to reduce premature loss of the grinding surface and extend the flap disc's life.

The Tiger Paw has a 7/8" arbor hole. And the maximum rotation spin speed is 13,000 rpm.

Sold in packs of 10.

Reasons to Buy

The Tiger Paw is a mid priced flap disc, well respected and popular because of its great performance at a solid price.

Reasons Not to Buy

Not for you if you are looking for the smoother grinding surface offered by 80 grit or 120 grit as these aren't available.

Won't last you as long as the Walter FlexSteel but then you're not paying FlexSteel prices

Tiger Paw Grinding Mild Steel

Tiger Paw Grin​​​​ding Mild Steel

In Conclusion

The Weiler Tiger Paw takes second place because it is not quite as performant or long lasting as the FlexSteel.  It also doesn't have the softer 80 and 120 grit surfaces when you want softer blending. That said 40 and 60 grit are the most popular grit surfaces to grind with. When you can't afford the cost of the FlexSteel the Tiger Paw makes a great alternative.

YouTube Video on the Weiler Tiger Paw

A 2 minute 18 second video that not only shows you the main areas you can use the Tiger Paw for it shows a comparison to a competitor (we don't know who) where it removed 25% more metal!

Weiler's Tiger Paw High Performance Flap Disc

​Video Credit: Weiler Abrasives Group

Worth a look on the Type 27 List!

Overview

The Kseibi comes in 40 Grit, 60 Grit, 80 Grit and 120 Grit

A flap disc designed to be used on mild steel and low carbon steel.

The Aluminum Oxide surface makes this flap disc one that won't stand up to a lot of wear and tear. Use on a small project, thin metal gauges, light mill scale or for smoothing your weld bead. Anywhere where heavy metal removing is not going to be needed.

7/8 ths of an inch arbor hole size.

Rotation max speed - 13,300.

Pack size: 10 pack

Reason to Buy

When you're on a budget and don't have much to smooth down, the Kseibi flap discs perform well. Just don't expect too much.

Reasons Not to Buy

Aluminum Oxide is the weakest, least robust surface for a flap disc. Buy for the light grinding of welds and polishing. 

In Conclusion

A good entry level flap disc and should do a job for you. Expect to go through a few of these if you are pushing what this flap disc surface is designed for.

Let's take a look at the Type 29 with the more curved flap disc surface.

Winner of the Type 29 List

Overview

Enduro-Flex Flap Disc

The Enduro-Flex comes in 40 grit, 60 grit, 80 grit and 120 grit.

With a Zirconia surface Walter Surface Technologies say is ultra fine for better metal removal and a top coat to make these flap discs work cool and with lower vibration when compared to other flap discs.

Designed to be used on mild steel, low carbon steel and stainless steel. If you have large surfaces with mill scale or rust to clean up. Or a lot of welding beads to blend in. Maybe a large contoured project to grind, these features make the Enduro-Flex less exhausting to use.

Can be purchased with round holes or threaded holes. The threaded holes mean that you won't need your tools to put these flap discs on.

The Enduro-Flex has a 7/8" arbor hole.

The total rotational spin speed is 13,300 rpm.

Pack of 10

Enduro-Flex Grinding Mild Steel

Enduro-Flex Grinding Mild Steel

Reasons to Buy

Walter claims these flap discs have the longest life and best material removal in the industry and I and a lot of other users agree.

The eco-trim backing means you can trim down the backing to make these flap discs last even longer. Be sure to trim the backing to get the most wear out of these discs

Reason Not to Buy

They are a premium flap disc and may stretch your budget too far.

In Conclusion

These Enduro-Flex are great flap discs but toward the pricey end of the flap disc market. Walter Enduro-Flex can be put on with no tools so are time saving. If you can afford them then this is the type 29 flap disc to buy.

YouTube Video of the EnduroFlex Flap Disc

This Walter Surface Technologies video is a bit of a wheeze. Try to see past the bad acting and it shows a good flap disc in action.

The Best Flap Discs Enduro-Flex

​Video Credit: Walter Surface Technologies

Runner Up on the Type 29 List

Overview

The High Density Jumbo flap disc is available in 40 Grit, 60 Grit, 80 Grit and 120 Grit.

It can also be purchased in a mixed pack that contains all the grit sizes. Useful when your project needs a selection of flap disc grit sizes but not so large to need 10 of each.

Designed to work on low carbon and mild steel.

The surface of this flap disc is a blend of Zirconia and Aluminum oxide. The Benchmark Abrasives also comes in a standard form the Premium Zirconia. It is worth noting that the High Density Jumbo flap disc wheel has more fiber on the flaps and is thicker and so softer. They also last longer.

If you are after a more aggressive grinding surface choose the ​Benchmark Abrasives Zirconia flap disc standard form. They won't last as long but if it is more material removal you're after they may well suit you better.

13,000 max rpm

The arbor hole is 7/8 ths of an inch.

10 pack

Reasons to Buy

The high density jumbo flap discs last longer and are better to use on thin grades of mild steel as they are softer.

Reasons Not Buy

Well, they aren't the Enduro-Flex, but are easier on your pocket.

In Conclusion

Lots of good user feed back with the Benchmark Abrasives Premium High Density Jumbo flap disc well regarded. They also stand the pace when used, particularly because of the price you might expect them to have worn through and need replacing.

The company does seem to want to go the extra mile to make sure their customers are happy with the product when the odd problem arises.

What Else You Will need Along with Your Flap Disc

Gloves to protect your hands. Goggles, preferably with side shields to protect your eyes. And ideally a face shield. Too many scared faces are the result of a hand grinder ejecting parts of a failing disc at speeds. And you're talking about your face stopping a piece of flap disc at speeds of 180 mph.

Angle your grinder guard to protect yourself and those standing near you.

Last Words

And there you have it. The 5 Best Flap Discs for Cleaning and prepping mild steel for welding. Do you buy the winners and the more expensive flap discs?

They are in my opinion the best.

Or buy something that is 2 thirds to half the price and compromise on how long the flap disc will last.

Sure if your project is smaller, perhaps is not too heavily rusty or dirty or you don't weld much, then the runners up may be just what you need.

The choice is yours.

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