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The Finishing Touch

From machines to media, a guide to mass finishing

By Shawna Kulpa, MJSA Journal

Are you looking to save time and effort at the bench? Are you interested in cleaner and healthier finishing options? Does the thought of one day losing a finger or chunk of hair to your polishing wheel keep you up at night? If so, then mass finishing may be just what you need.

Long thought to be something only mass manufacturers used, many jewelers making multiples have put finishing tumblers to work in their studios. But are they right for you and your business? To help you decide, we checked in with a few mass finishing experts about the process, and they shared details about what the process entails and the machinery and materials involved. They also offered a few tips that can help your finishing be a massive success.

Why Should You Consider Mass Finishing?

Mass finishing is just what it sounds like—you’re finishing a mass of pieces at one time rather than one at a time. So, in determining if mass finishing is right for your business, you’ll want to consider a few factors.

How many pieces will you be finishing—and how much finishing will they need? If pieces need to undergo multiple processes (material removal, burnishing, and polishing), the total machine finishing time could take more than 24 hours. However, remember that the machines are doing the work during that time, freeing you up to work on other pieces.

“If you’re a small custom jeweler only putting out a couple pieces a day or week, it doesn’t make sense to do mass finishing because it takes a lot longer than it would to hand finish a piece,” says John Sartin, a member of the tech team at Rio Grande in Albuquerque, New Mexico.

What types of pieces are you creating? In addition to considering the number of pieces to finish, think about the design of those pieces, as some types are better suited for mass finishing. According to Judy Hoch, owner of Marstal Smithy in Salida, Colorado, textured and detailed pieces are ideal for mass finishing, as the media used for polishing can easily reach tiny spots in those details that would be difficult if not impossible to reach with a polishing wheel or buff. In addition, mass finishing won’t remove any of the detail that conventional hand buffing might remove. Hoch also says that small pieces such as charms are good candidates for mass finishing as well since they can be hard to hold.

Is mass finishing a safer option? If you do produce multiple pieces but aren’t sure they warrant the investment, consider the safety benefits that mass finishing offers. Hoch considers it the safest way to finish jewelry, especially chains.

“You don’t catch your fingers on a buff,” she says. “You don’t breathe dust. For people with allergies or who are sensitive to dust, mass finishing is the best choice you have. In terms of making a shop safe, it’s a better answer.”

What type of quality do you need? Another factor to consider is the quality of the finish that can be achieved. Hoch has found that mass finishing produces a more even finish on pieces than manual buffing. It also avoids the drag lines that a buff can leave behind.

Will it save metal? One final reason why you may want to consider mass finishing is the reduced metal loss it offers. According to Hoch, who’s conducted research in this area, normal jewelry finishing by hand on a buff removes about 8 percent of the precious metal weight. “Mass finishing removes under 0.5 percent,” she says.

The Machines

If you’re still thinking of mass finishing your jewelry, you’ll next have to consider the type of equipment you’ll need—and its cost.

There are four types of machines suitable for finishing jewelry work: rotary, vibratory, magnetic, and centrifugal.

Rotary tumblers (also known as barrel tumblers) are the ones most jewelers likely picture when they think of mass finishing. The original mass finishing machine, these units are frequently used for rock tumbling. As the barrel rotates, it allows the workpieces inside to roll around with the media. Simple in design, the machines excel at burnishing workpieces.

“A rotary tumbler won’t smooth anything, it will just make it shiny,” says Hoch. The media in the tumbler acts like tiny hammers, hitting the metal but not smoothing it.

Rotary Tumbler

Since the machines aren’t designed to smooth items, you would need to pre-finish your pieces before dropping them in the tumbler. Sartin recommends pre-finishing your pieces to 600 grit. “It’s not going to remove scratches, parting lines, or other casting defects on the surface,” he says. For that, you’ll need to use abrasive media in a vibratory tumbler in a process called cut-down.

In addition, it’s important that the inside walls of a rotary tumbler be flat. (Often, the barrel is hexagonal or octagonal, depending on its size.) “People use mayo jars and they don’t work,” Hoch says. That’s because the media being used to finish the jewelry pieces needs to continually hit those pieces. If the sides of the tumbler are rounded, the media will simply slide around the barrel. She notes that many of the rock tumblers that jewelers may initially start out with because of their low price usually have rounded barrels. “The competent rotary tumblers with flat sides tend to be more expensive than the rock tumblers,” she says. “Buy quality or you’ll buy it more than once.”

Vibratory tumblers are likely to be your best option if you want to remove material (known as cut-down), though they’re also suitable for polishing and burnishing. These machines use vibrations to move the workpieces and media throughout the tub, allowing them to rub against each other. Cycle time depends on the condition of the pieces when starting and whether they are cast or fabricated, as cast pieces can require two abrasive runs—one coarse, one fine.

(left) Vibratory Tumbler, (right) Magnetic Finisher

While vibratory tumblers can be used for burnishing, it requires special, heavy-duty machines due to the weight of the media needed. Also, they offer no time advantage over rotary tumblers when it comes to burnishing.

Magnetic finishers can be used for polishing small parts, such as basket settings. The machine burnishes using very small stainless-steel pins (which measure around 0.5 mm by 5 mm). The small pins can get into tiny spaces that larger media in other machines may not reach. Because the pins are magnetic, they can be easily separated from the workpieces. They can also be used to clean investment from castings. “It leaves a slightly sparkly finish that later can be hand polished or burnished with stainless steel in a rotary tumbler,” says Hoch. “It is my go-to machine for polishing handmade ear wires.”

Finally, there are centrifugal machines. Sartin likens these devices to a Tilt-A-Whirl, where the machine spins and the media is moved around quickly by centrifugal forces. Because the media moves around so quickly in them, these machines finish pieces much faster. “Cut-down could be in as little as 2 hours,” says Sartin. Suitable for polishing and cut-down but not burnishing, they usually require fixturing to keep pieces from impinging. (Impingement is when jewelry pieces rub and bump into each other, which can lead to scratches and dents.) In addition, these machines are geared toward mass manufacturers due to their size and hefty price tags.

That price tag is another important consideration before you take the plunge. Standard centrifugal machines have prices that start in the thousands, whereas a decent rotary tumbler can be had for around $400. A small, basic vibratory tumbler can be purchased for about $100 but a good vibratory flow-thru tumbler would cost around $500. Small magnetic finishers run around $300 and often have only a timer; larger versions offer speed control but come with a price tag that can run between $1,000 and $2,500. Prices of tumblers do increase with the size and capacity of the machine, and large, high-quality rotary and vibratory tumblers can easily run into the thousands.

Before investing in any type of tumbler, you should consider the types and sizes of the pieces you’ll likely be finishing. “One criteria is that your work can move freely in the machine,” says Hoch. She recommends putting the piece in the unit you’re considering buying and rotating it to see if it could tumble freely, particularly any large pieces such as cuff bracelets. “Impingement is a problem.”

If mass finishing makes sense for your business, Hoch recommends opting for both a rotary and a vibratory tumbler, noting that the initial investment will pay off in the long run.

“Good tumblers are basically bulletproof,” she says, noting that most high- quality tumblers require little ongoing maintenance, though with cheaper rotary tumblers you’ll likely have to replace the belts. “They’re one of the most reliable pieces of equipment in the jewelry industry—if you buy a good one,” she says.

The Media

Regardless of the type of finishing work you’ll be doing, you’ll need some type of media to work on your pieces. The type you’ll use will depend on your goal.

If you’re cutting down pieces in a tumbler, you’ll need an abrasive media that will grind against the workpieces, removing material as it does so. Abrasive media has two parts—the carrier and the cutting component.