Written by Christopher Stone, Owner Lehigh Valley Abrasives, a full service provider of abrasives to the welding and metalworking industries (www.lehighvalleyabrasives.com).

Flap disc grinding weld smooth.

A weld cleaned by a unitized disc.

Flap disc photo.

The use of a unitized disc.

A weld ground smooth by a flap disc.

A large number of new abrasives – and more powerful right angle grinders – have been introduced in the last several years that allow improved cutting, grinding and finishing, and anyone involved in the metalworking industries should know that choosing the correct tool and abrasive can reduce finishing time and costs.

The right angle grinder is the most widely used tool in any metalworking shop. New developments in the grinder itself include more powerful variable-speed motors, improved ergonomics, and designs that dampen vibration.

When using the right angle grinder to perform different tasks, newer grinders allow the user to adjust the speed of the grinder. This becomes critical when the operator changes from grinding to polishing. Polishing requires slowing the speed for finer finishing, and that becomes critical to the aesthetics of the final finish of the surface. In addition, studies show that altering the speed of the grinder to the correct level can double the working life of the abrasive that is being used.

For individuals who use the grinder for a long period of time each day, the new ergonomic and vibration-dampening designs from companies such as Metabo, Fein, and Makita can reduce repetitive-use injuries and can cut worker downtime. This is because the vibration from the grinder is absorbed by the handle, not transferred to the worker. Also, new designs make the grinder lighter, which reduces operator fatigue and allow for optimum hand positioning while grinding.

Abrasives for Use on the Right Angle Grinder
Cut Off Wheels
When cutting with a right angle grinder, the advent of thinner, slicer/cut off wheels has allowed faster cutting with less material loss. The new, thinner, type 1 wheels minimize the surface area contact between the material and the wheel due to the reduced surface width of the wheel.

The reduced surface cutting area provides the following benefits:
1. It requires less force for cutting.
2. It reduces base material loss during the cutting operation.
3. It generates less heat.
4. It improves surface finish on the cut material.

These new, high-quality wheels use a mixture of aluminum oxide and zirconia grains and reinforced layers of mesh to improve cutting life. The new thinner cut-off wheels can be found in diameters ranging from 3 in. to 7 in. and at thicknesses of .035 in. to .045 in.

When working with stainless steel or other high-nickel alloys, cut-off wheels that are sulfur- and chloride-free should be used to prevent contamination of the workpiece. High-quality wheels from reputable manufacturers should be used, and the proper guards and flanges should be in place when cutting. An inferior wheel could blow apart because of the thinner designs and present hazards to operators.

Flap Discs
For material removal, including weld grinding, blending, and deburring, the angle grinder is the workhorse of most metalworking shops. For most material-removal operations, the two step process of grinding wheel then fiber disc finishing has been replaced by the use of flap discs. The recently introduced flap disc grinds and finishes in one step, reducing both the time needed and expenses for finishing a product. In addition, with a variable-speed grinder and flap disc, a user can extend the working life of the flap disc by 50 percent by keeping the angle grinder’s rpm between 5,000 and 8,000.

The advantages of the flap disc are:
They remove material aggressively, with removal rates equal to depressed-center-wheel grinders.
Their tough construction allows for aggressive edge grinding.
They grind and finish at the same time, saving time and money.
They provide a better-finished surface.
They require little surface pressure, so they provide cool cutting conditions that permit light contouring while avoiding burning workpieces by overheating.
They ensure consistent performance because new abrasive particles are continually exposed during use and over the life of the product.
They are easy to use.
They offer safer working conditions than alternate wheels.
They are designed as lightweight tools, so they reduce operator fatigue.
They last as much as 30 times longer than conventional fiber discs because of their overlapping flap construction.

However, the quality of flap discs varies from manufacturer to manufacturer.

The following qualities should be considered when choosing a flap disc:

1. The type of coated abrasive
Good: Aluminum oxide is suitable to most general purpose applications. It is specified for use on wood and most metals.

Better: Zirconia alumina grains are sharp and durable and provide fast stock removal and longer life. They are used to greatest advantage in coarse grits on heavy-duty metalworking stock removal applications. Zirconia alumina usually will last twice as long as aluminum oxide.

Best: Ceramic grain are available in a variety of series as special products for aggressive and cool grinding. These abrasives ensure faster grinding while, at the same time, offering better surface quality and excellent stock-removal rates. The cool grinding properties of ceramic abrasives extends their service life, while preventing surface discoloration of the workpiece. Ceramics are applicable for grinding high alloyed steels, titanium, nickel alloys and all extremely hard materials. Ceramics usually will last 50 percent longer than zirconia alumina abrasives.

2. The manufacturer of the coated abrasive flaps that are glued to the backing of the flap disc.
There are almost no U.S. companies that manufacture coated abrasives.

Many people consider that European abrasives suppliers, such as Norton (www.nortonabrasives.com), VSM (www.vsmabrasives.com), and Klingspor (www.klingspor.com), provide the leading products, and care should be taken because inferior products are manufactured that might cost less, but will not last long when put into use.

Other factors which play a role in the life of the flap disc include the durability of the backing material, which is made of either fiberglass or nylon, and the number of flaps that are laid on the disc. Higher quality discs are made with extra layers of fiberglass backing and additional coated, abrasives flaps.

Alternative discs and wheels
The prevalence of right angle grinders has led to the adaptation of a number of newer abrasive products that are tailored to cleaning and finishing.

They include these items:
Clean and strip discs.
Clean and strip discs clean metallic surfaces without material removal. They are a safe alternative to wire brushes.
The primary applications for clean and strip discs include;
Removal of paint and adhesives.
Cleaning of weld seams.
Removal of welding scale and discoloration.
And, surface preparation for auto body work.

Surface conditioning discs and surface conditioning flap discs.
Surface conditioning discs are made with open nylon webbing that is impregnated with abrasive grains. They offer a continuous and controlled finish with minimal material removal, are flexible, and allow polishing of contoured surfaces.
Surface conditioning products are used heavily in the stainless steel fabrication industries to provide a satin finish to the base material and welds.
Additional applications include:
Gasket removal.
Coatings removal.
Cleaning weld splatter.
Removing heat discoloration.
Graining stainless steel material.

Type 27 unitized wheels.
Type 27 unitized wheels are an excellent choice for the final polishing step on stainless welds because they blend tool marks, remove surface imperfections and leave a bright clean finish on stainless steel, titanium, and aluminum.
These unitized wheels are composed of layers of nonwoven material that is impregnated with abrasive grains, then pressed together into their final shapes.
The unitized wheel design allows for edge grinding and provides access for grinding welded joints that sometimes cannot be reached with a flap disc.

Newer abrasive materials last longer, provide an improved surface finish, and get the job done faster and at a lower total cost and, combined with the new designs for right angle grinders, can be used to accomplish most finishing tasks as a single tool.

Today’s angle grinders are more powerful and safer due to improved ergonomics and, with their latest designs, allow the right angle grinder to maintain its role as the king of the handheld power tool in the metal-finishing arena.