7 Things Machinists Need to Know When Choosing Abrasives

To get the most out of abrasives in machine shops, you need to know a lot more than the old tip for using sandpaper: “rough side down.”

That’s according to Norton | Saint-Gobain Abrasives’ National Account Manager Brad Heraghty, who notes that, given the wide array of high-quality abrasive products on the market today, choosing one can be a confusing exercise.

“We manufacture more than half a million different part numbers, and choosing the best one for the job comes down to what you’re trying to accomplish,” he says. “You shouldn’t pick an abrasive product that will be overkill for the application, thereby wasting money, but you also need to consider efficiency.”

To make it simpler, Heraghty groups abrasives into five broad categories based on business units:

• Bonded abrasives: A group largely composed of wheels—surface grinding wheels, bench and pedestal wheels, centerless grinding wheels and so on.
• Coated abrasives: A group that includes traditional sandpaper and abrasive belts as well as pressure-sensitive adhesive (PSA) discs like you might use on an orbital sander or pencil grinder.
• Non-woven products: Includes hand pads and convolute wheels such as the ones used to deburr parts, not to mention the hard, screw-on wheels found on right-angle grinders. These are primarily for weld preparation and cleanup afterward.
• Superabrasives: Products such as CBN, or cubic boron nitride, and diamond that provide greater precision and overall grinding performance, although at a higher price point.
• Thin wheels: Easily mistaken for bonded wheels but labeled “organic” because they use a resin bond that breaks down with heat.

“An organic wheel provides higher stock removals but is less suitable if you need to hold tight tolerances,” Heraghty says. “It’s the opposite of a vitrified bonded wheel, which is brittle, almost like glass, and best for precision grinding and lighter stock removal.”

Don’t Settle for the Wrong Choice

He warns readers to take such advice with a grain of salt, however, since abrasive selection is dependent on material, application, production quantities, budget constraints and a host of other factors.

Some shops lean toward general-purpose abrasives, or “tweeners,” due to A) their lower cost and B) the notion that operators will fail to achieve the potential benefits of a high-performance product like 3M’s Cubitron, he notes.

“That’s unfortunate,” he says. “For instance, you’ll typically get the job done more quickly with a fiber disc in certain applications, but many shops will use a flap disc instead because they’re more forgiving. By investing in some operator training, the shop will see greater throughput as well as maximum value for their abrasive spend.” 

In the same vein, some managers and purchasing personnel might complain that operators throw away discs that have many hours of life left. Why buy a more expensive product, even if it does provide more performance? Here again, a little training will bring big benefits.

In the case of the fiber disc just mentioned, Veeninga equates it to buying a race car and putting the wrong tires on it—the shop floor equivalent of using a backup pad that’s too soft.

“In this situation, the minerals aren’t allowed to stand up and do the work for you,” he explains. “The wheel loads up and grows dull because the coated abrasive can’t break down and expose new cutting edges. This is exactly what we’ve designed precision-shaped grain products like 3M’s new family of Cubitron 3 products to do.”

Finally, failure to keep current on technology and ask for a helping hand from your abrasives supplier can mean losing out on recently introduced improvement opportunities. Veeninga points to quick-change mounting systems as one example.

“Attachment methods like PSA, hook and loop, and traditional backup pads with a retainer nut are perfectly fine for many applications, but 3M has developed a backing system that lets the operator give the wheel a quarter-turn to secure the disc,” he says. “This is much faster than the traditional alternative, and even though it is an added cost, we’re finding that many people prefer it thanks to its convenience and overall cost reduction.”

What tips do you have for choosing the best abrasive? Tell us in the comments below.