More than 5,000 years ago, metal-polishing skills and tools were developed to bring a gleam to soft precious metals such as gold, silver and bronze. Today, you may use those time-honored techniques to polish flatware for the holidays. But youíll need to expand your repertoire if you want to bring a shine to harder metals such as steel.
Polishing metal is somewhat akin to sanding wood: You start coarse and end fine. You may even begin by cleaning the part youíre working on with sandpaper to remove nicks and scratches before you turn on a power tool. But once the rough work is out of the way, youíll shift to metal-polishing compounds, which are waxy materials loaded with grit. When you apply it to the correct polishing wheel, the compound sticks, and the magic of bringing a real shine to metal can begin.
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The equipment you'll need to polish metal is pretty simple: a polishing machine and an assortment of wheels and abrasives. The machine is a task-specific tool with longer shafts than a bench grinder (which it resembles). Those long shafts create enough clearance that you can mount larger polishing wheels for increased surface contact, and they allow for more room to maneuver the item youíre polishing. If you already own a bench grinder, you can use it for polishing, but youíll need to remove any guards that would get in the way of the polishing wheels. A corded drill can also be used as an effective polishing machine, especially when youíre working in tight quarters or on parts that you canít remove and bring to a bench.
Different polishing wheels perform different tasks. The most common wheels are made from cotton and come in a variety of sizes. Sisal wheels are impregnated with fibers similar to stiff twine that produce a rougher cut and are ideal for beginning the polishing process. Light, minimally stitched wheels are softer and allow you to really press the part youíre polishing into them ñ ideal if there are lots of small nooks or crevices in the workpiece.
For polishing wheels to work, they need to be coated with an abrasive compound. Generally speaking, compounds range in grit from dark to light, with black being the coarsest, then gray, brown and white, which are progressively finer. Blue and red bars of compound are designed to buff precious metals or metal plating to a brilliant shine and have no abrasive qualities, and green compounds are typically intended for stainless steel.
You'll need to prep the piece to be polished by first removing any debris (which, when spinning at several thousand revolutions per minute [RPM], would have its own abrasive effect). Sand away larger scratches and imperfections because attempting to buff them out will only create large divots. Gradually work from coarse sandpaper to finer paper or steel wool before you move on to polishing compound.
The idea when polishing is to let the abrasive compound do all of the work, and that requires speed. Professionals measure this effect through a term called surface feet per minute (SFPM). To determine the SFPM, you multiply the RPM of the polisherís motor by the wheel diameter and then divide by 3.82. So for example, if we know that the buffer rotates at 3,450 RPM and we're using an 8-in. wheel, the equation would be (3,450 x 8) / 3.82 = 7,225 SFPM. The goal when polishing is to be between 4,000 and 7,500 SFPM.
You'll apply polishing compound to the polishing wheel as it spins. Apply the compound lightly and frequently or the wheel will simply fling the substance all over you and your workspace.
Touch the workpiece to the polishing wheel, for tips on positioning the workpiece in relation to the wheel). Donít forcefully push the workpiece into the wheel (thatís only necessary when you need to get into tight places). Slowing down the wheelís speed by force only slows down the polishing process.
As you progress from coarse compound to finer compounds, remember to change the wheel ñ use a different one for each type of compound. When working with coarse compounds to remove stubborn corrosion or imperfections, move the workpiece against the rotation of the wheel to create a cutting effect. But when you use finer compounds, work with the rotation of the wheel to create more of a buffing effect.
The piece you're working on will dictate how much preparation and polishing each stage will require. It takes more work to bring a shine to harder metals such as iron and steel than it does to polish aluminum or brass. But with the right tools and techniques, you can achieve brilliant results on any type of metal.
Tips for Working Smart
Whenever youíre polishing metal, safety is paramount. Remove all jewelry, including your watch, so it canít get caught by a wheel. Always wear safety goggles and gloves - metal can get very hot during the polishing process. Wear a protective apron or coveralls, as the dust from the process can be messy and sticky, and a dust mask to keep you from inhaling any airborne particles. Pay attention to the position of your workpiece in relation to the polishing wheel. If the wheel is rotating downward, position the workpiece on the bottom half of the polishing wheel. Conversely, if the wheel is rotating upward, ensure that the part is on top. That way, if you lose your grip on a part, it will be projected away from you.
About the author:
Wes Thomsen is an avid old-car and motorcycle enthusiast and is the Web Video Producer for HANDY.