It’s important to keep safety in mind when using abrasives with power tools. A lot of metal can be removed in a hurry, but it comes off as a shower of hot sparks, and it’s essential to protect your eyes, face, and body from injury. A full-face shield is recommended, along with heavy gloves—and be sure to avoid clothing and footwear made from synthetic materials, which can melt and stick to your skin. Hearing protection is highly recommended too, since a grinder working at full song puts out a lot of noise.

There are some additional safety issues to consider, as well. When sanding near an edge, it is important to keep the rotation of the disc oriented so it goes OFF the edge, rather than rotating TOWARD the edge. This strategy will help to prevent the edge of the disc from grabbing the metal edge, which can be very dangerous.

Abrasive cut-off wheels can be used with handheld electric or pneumatic grinders, and they can easily make straight or slightly curved cuts in everything from sheetmetal to heavy plate, plus they work well on shapes like rectangular and round tubing and bar, angle iron, and channels. When using a cut-off wheel, it’s important to use a guard that shields the disc, protecting the operator from any flying debris.

Grinding discs are perhaps the most widely used abrasive product; they come in a very broad selection of diameters and grits and they are engineered for particular applications. While the most common abrasives are designed to work well on mild steel, there are some specialized products that are designed to cope with the particular challenges posed by stainless steel and aluminum.

Pay particular attention to the photos that accompany this article, which show how you can smooth a weld—even on thin sheetmetal—without reducing the material thickness significantly. The key is to orient the disc so the grains travel along the length of the weld rather than cut across it. As you’ll see, you can make a weld nearly invisible by using the proper techniques, using only a small number of abrasive products.

Another principle that applies to the whole spectrum of abrasives is to let the tool do the work, without forcing it. When you apply excessive pressure, it generates more heat—and unnecessary heat will cause the abrasive medium to break down much more quickly than necessary.

It’s also important to change abrasive discs when they start to get dull. Using a badly worn disc can cause excessive heat in the workpiece, which can actually distort thin parts like truck body panels.

3. Pneumatic grinders are very compact and come in a range of sizes and power levels. They do require a good air compressor, which not everyone has.

5. There are a lot of good cordless grinders available, and while larger than air tools they do not need a power cable, which means you can use them anywhere.

7. Grinding wheels are ideal for removing a lot of metal in a hurry, like large weld beads and parting lines on cast or forged components.

9. Flap wheels have the ability to blend and smooth large uneven surfaces.

11. There are important principles for any grinding operation. Discs work best when held at a low angle to the part, usually about 10 degrees. A steeper angle forces the grains at the edge of the disc to do all the work.

13. Heat will degrade the abrasives quickly, so light to moderate pressure works better than high pressure.

15. Here’s a 3-inch-diameter 80-grit disc being used to cut a weld down flat.

17. Once the weld is cut flat with an 80-grit disc, a medium nonwoven surface conditioning disc can be used to remove the visible scratches.

19. For the finest finish, the area can be hand grained with a nonwoven pad.

21. Cylindrical flap wheels come in a broad array of widths, diameters, and grits. They are ideal for inside curves or for getting into holes.