Cutoff wheels, grinding wheels and flap discs have made the job of welders and other operators easier because they provide a quick and simple way to cut or otherwise process metal pieces. The goal when cutting material is to use the fastest method to produce the highest acceptable quality result. Finding the balance between the two is always a challenge.
When choosing which cutoff wheel, grinding wheel or flap disc to use, a good place to start is looking at the profile of each. One of the most common mistakes operators make is using the wrong wheel for the job.
“I was a fabricator for a number of years while going to school for industrial design,” says Elliot Sheperd, associate product manager at Weiler Abrasives. “Starting out as a shop hand and moving on to welding, you get a sense of just how often people use whatever everyone else is using. But, they don’t really understand why they are using it. They just use what’s on the shelf.”
What’s The Difference?
A Type 1 cutoff wheel is a flat disc for cutting straight into the workpiece at a 90-degree angle. These wheels offer versatility and work well when cutting corners, angle iron, C channel or anything that requires the operator to cut up and over two different planes. Their advantage comes from their ability to offer more cutting surface than Type 27 cutoff wheels.
Type 1 wheels are also more flexible than Type 27 wheels, which means they are more receptive to twisting and bending.
“In general, Type 1 wheels give the operators increased control, especially when cutting over corners and extrusions,” Sheperd says. “The Type 1 profile has an increased cutting surface and less potential to interfere with the workpiece.”
The main disadvantage of the Type 1 wheel is that the operator can’t make as close of a flush cut compared to a Type 27 wheel. Type 27 wheels are extended a bit off of the angle grinder or other power tool so the operator can get more of a flush cut across that plane.
Due to mounting closer to the guard, Type 1 wheels may require a different guard position depending on the profile of the workpiece.
“To get those cuts done right, a lot of people, including me, score the line first,” Sheperd says. “Some use a marker to mark the line, but it is hard to see it with all the sparks coming through. But by scoring the line first and then understanding the motion of the way your arms need to move, you can almost give yourself muscle memory. For a very strategic cut, I follow those lines with the grinder turned off a couple times just so I understand where I need to be and then engage the cut from there.”
Type 27 wheels are for applications where additional offset from the grinder is required. In maintenance or repair applications, bolts and brackets often need to be cut off as evenly and close as possible. Also, when making long cuts off-hand, operators sometimes choose to use a piece of angle iron as a guide. Type 27 wheels allow the operator the ability to run long cuts along a guide for increased precision and accuracy.
With Type 27 wheels, the operator must be careful not to plunge too deep into the cut, as the depressed center can interfere with the material being cut and, ultimately, compromise the structural integrity of the wheel.
“Plunge cutting with a Type 27 wheel requires more attention and skill,” Sheperd says. “If you start to interfere with that depressed center – once it starts to rub against the material – it’s going to take some of the reinforcement out of the wheel and the wheel will fail. We’ve seen that a number of times.”
Also, wheel life is going to be reduced because the wheel cannot perform the full amount of cut with that depressed center.
Safety First
Producing the fastest, cleanest cuts is, of course, the end goal, but that objective must always be balanced with the best safety practices available. To achieve both, here are a few rules of thumb to follow when using abrasive wheels.
Always enter the cut from a section with less surface area where the material is the thinnest and use even pressure and consistent motion through the cut. Let the wheel do the work.
Check that the maximum rpm rating on the wheel is equal to or higher than the maximum rpm rating of the angle grinder. Using a wheel with an rpm rating lower than the grinder compromises operator safety.
Use the proper guard for the Type 1 or Type 27 wheel.
Always consider the angle of approach and choose the most appropriate product and profile for that application. Type 1 cutoff wheels are designed to be used at 90 degrees from the material, whereas Type 27 and Type 29 profiles offer varying degrees of versatility.
Wear proper personal protection, such as eye, face and hearing protection and safety gloves.
Check all wheel for cracks or damage before use and handle and store them carefully. “I’ve seen multiple shifts where the operators use the same wheel on the same grinder without ever checking the integrity of the wheel,” says Elliot Sheperd, associate product manager at Weiler Abrasives. “I would always remove the wheel and inspect it on both sides to make sure there were no cracks and no fiberglass backing showing. If I had another shift coming up, I’d take the wheel off of the grinder and stick it in my toolbox so no one else could use it.”
Sheperd also advises to never use a product that is suspect or shows signs of damage. And to always allow the wheel to run at full speed prior to touching the workpiece. “While holding the grinder away from you, allow the wheel to come to full speed and then jog the wheel (allow it to slow and come back to full speed) two to three times prior to use. ANSI recommends that cutting wheels, grinding wheels and flap discs be allowed to run a free speed for 60 sec.”
Grinding Types
For grinding wheels, Types 27 and 28 are the most common, although some companies offer Type 1 wheels. Type 27 grinding wheels are by far the most effective for use on right-angle grinders. They provide fast, aggressive stock removal and are used effectively at a variety of grinding angles.
“The depressed center provides a lot of structural rigidity so when you do push it at a 35-degree angle, for example, there’s no chance of bending, waving or something else you don’t want,” Sheperd says.
Type 28 grinding wheels are a saucer-shaped disc, generally available in the larger 7-in. and 9-in. diameters. Type 28 wheels allow for increased aggression in applications that require shallow grinding angles (less than 10 degrees).
The Flap
Some jobs call for a flap disc and the flap disc profile – Type 27 flat shape or Type 29 conical shape – provides different performance features.
Type 29 flap discs are the best choice for aggressive stock removal and higher grinding angles. They have angled flaps and may be used on both flat surfaces and for beveling and chamfering. Type 27 flap discs are the best choice for blending and smooth finishing and are used primarily on flat surfaces.
“With flap discs, if you have more of a steep grind, say 15 to 35 degrees, a Type 29 disc can provide more disc life,” Sheperd says. “We’ve had customers wonder why they aren’t getting proper wear on their flap discs. In many cases, we’ll discover that the operator is grinding at a very steep angle with a Type 27 disc. They wear out half of the front of the disc and then say it’s used up. We give them a Type 29 version of the same flap disc and the result is much greater disc life while still following the same grinding process.”
Type 29 flap discs also typically see increased cut rates because more abrasive surface contacts the workpiece.
On the other end, for an operator blending and finishing a flat seam, the Type 27 flap disc is going to be a better recommendation for the lower grinding angle and lighter pressure used during those blending and finishing applications, Sheperd says, because at that flat angle, it provides a bit more surface area and a flat grind.
While there are other factors that affect wheel choice – the abrasive grain being the main one – starting with the right profile is a good place to begin. Even though a job can be completed if the wrong wheel is used, it may take longer and require more secondary cleanup. Using the best wheel for the job saves time and post-processing efforts.
