From machines to media, a guide to mass finishing
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.
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.
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.
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.
According to Hoch, most abrasives are plastic and use a garnet or corundum cutting component. “The abrasive media has cutting bits throughout each piece so as the media wears, it continues to work,” she explains. She also notes that very abrasive media sometimes has a ceramic carrier, giving the media more weight. “The weight of the abrasive media matters as much as the cutting component.”
Abrasive media typically comes in different shapes (usually cones, pyramids, and cylinders) and in a range of sizes and grades (often coarse, medium, and fine). Each shape is going to work on your pieces appropriately to the shape they are.
For example, “if pieces have angular geometry or areas that cone-shaped media couldn’t touch, you want to use pyramid media that will get into those details. Pyramid media reaches into tighter spots,” explains Sartin. "Alternatively, if you’re finishing smooth, round wedding bands with no details you wouldn’t want to use pyramids because their sharp angles could damage the bands.” Instead, you would want to consider using cone media: “They’re designed for smoother, rounder shapes,” he says.
However, because you’re not likely to be working in just one style, you can mix the media to “satisfy both worlds,” says Sartin.
If you’re looking to polish your workpieces, you’ll want to use a burnishing media. These are designed to smooth and brighten the surface through a rubbing action. The most common type of burnishing media is steel shot, which also comes in a range of sizes and shapes. There are two types of steel shot—carbon and stainless—and each has its own pros and cons.
Carbon steel shot can be used on all metals except for platinum. It’s less expensive than stainless steel but requires much more maintenance, as it can easily rust and contaminate workpieces during the tumbling process. The rust can also result in pitting in the shot, which can lead to rougher surfaces on your workpieces.
Although more expensive, stainless steel shot can be used on platinum pieces (though you’ll want to check with the manufacturer or supplier). It’s also less susceptible to corrosion and requires less maintenance. According to Hoch, you can expect stainless media to outlast you, provided you take care of it. She also notes that stainless shot should be used only in rotary tumblers due to its weight. “You’ll wear out the smaller tumblers,” she says. “There are vibratory tumblers for stainless but they’re horribly expensive.”
If you’re debating between the two steel shots, stainless is the better option. Otherwise, “you’ll have to keep it clean in a rust-inhibiting solution,” she says. “The money you save isn’t worth the time it takes to keep it from rusting. All it takes is for one piece of carbon shot to rust and you will contaminate the steel and all the jewelry in that burnishing run.”
A final polish is done with some kind of organic compound. It’s usually in the form of walnut shell, corncob, or wood shapes. It will be charged with a polishing compound, such as rouge or iron oxide.
Hoch currently uses a dry media that’s a blend of walnut shells, garbanzo beans, rice, and diamond compound. “This stuff is amazing,” she says. “You can run opals in it without scratching.” However, she notes that the media is not cheap ($140 for 5 pounds) so it’s not something many beginners will likely want to use. “If you had anticlastic gold earrings you want to shine like the sun, put them in this for a couple of hours and they’ll be beautiful.”
Regardless of what type of media you’re using, pay attention to the guidelines for your tumbler when determining how much media to use. “All tumblers will have a media requirement,” says Sartin. “If you look at the specs, it will state the weight of the media you need to use.” As you would expect, larger tumblers have larger requirements, so take that into consideration when deciding on the best size to buy. “There’s a great possibility of impinging if not enough media is used.”
Unless you’re using organic media (which is always run dry), you’ll need to include a liquid solution in the tumbler. There are different solutions on the market, and they all help to keep the media clean, adjusting the pH of the water used in wet tumbling and flushing away any media debris build-up.
While some jewelers are happy to rely on a mix of water and dish soap, Hoch recommends sticking with a solution that’s specifically designed for mass finishing. “Everyone with a jewelry supply business has a formulated liquid intended to clean, lubricate, and preserve the media,” she says, pointing out that even steel media needs “something more than Dawn.”
There are two types of solutions: deburring solutions (for use during cut-down) and burnishing solutions (for polishing and burnishing operations). Not using a burnishing solution is “like washing dishes without water,” says Hoch. “It doesn’t work.”
“If you don’t have a deburring solution in your water, as the pieces are sanding, the abrasive can drag across the piece and it doesn’t cut as it should,” explains Sartin. “With deburring solutions, there’s a component to them that helps the sludge fall out of solution. It concentrates that sludge.”
Unless you're using organic media, you'll need to include either a deburring or burnishing solution in a finishing run to adjust the pH of the water and flush away media debris.
Either solution should be checked and replaced regularly. If you’re cutting down in a vibratory tumbler, Sartin recommends changing the water hourly, since the particles that wear away from the abrasive media can create sludge. That sludge can build up in the tumbler and prevent the cutting action.
Some vibratory tumblers and centrifugal machines come with a flow-through system, which injects water at the top of the tumbler and has a drain at the bottom that pulls out used solution and sludge. If your machine is a closed system, you’ll need to empty the liquid and then rinse off the media in a strainer manually.
“If you’re running serious batches, you need a flow-through liquid,” says Hoch. “You want to have the liquid come into the tumbler, clean the pieces, and then go out a drain while the machine is running. If not, you’ll need to clean the liquid hourly, which is a nuisance.”
Tips for Tumbling
Although the process may seem fairly straightforward—drop workpieces into tumbler, press start, wait, and then retrieve your pieces—there are some things you’ll want to do to avoid problems.
• Don’t overload the tumblers. If you put too many pieces in, they’ll hit each other and you’ll get impingement marks on the pieces. “Impingement is probably the worst problem in mass finishing,” says Hoch. “Jewelry needs to be able to move inside the tumbler freely.” She says a good rule of thumb to keep in mind is that your pieces should take up no more than 10 to 15 percent of the volume of the tumbler.
• Keep things together. If you’re finishing lots of small pieces, Hoch recommends stringing them together with stainless-steel binding wire or electrical ties. That way, “there’s no Easter egg hunt trying to find the pieces,” she says. To prevent the items from bumping into each other, you can put a double twist on the wire to secure them.
• Set the amplitude. Sartin points out that some vibratory tumblers allow you to set the amplitude (the vibration intensity), which is controlled by weights attached to the axle at the bottom of the machine. “When the weights are in line, it runs really smooth,” he explains. “When they’re out of alignment, the vibration can increase because you’re throwing off the balance.”
Most tumblers have a factory setting that is at the most aggressive, but you’ll want to adjust the amplitude based on the media that you’re using. “If you don’t do that and you’re using it for dry finishing, you can impinge your pieces to the point where they’ll look like a golf ball,” says Sartin. If you’re unsure about the best setting to use, he adds, consult the machine’s manual. “Always read your manuals!”
• Dispose of materials properly. When you’re disposing of wet solution from your tumblers, never dump it down a drain. Because the media abrades itself during the finishing process, that material will accumulate in the solution and can clog your drain. “You can pour it on your roses, but don’t put it down the drain,” warns Hoch.
"It's best whenever you get your equipment to start doing practice runs. Take the time to understand the equipment, the media, and write it all down. Once you know, it's plug and play." —John Sartin
• Watch what you mass finish. While many jewelers may share stories and photos of gem-set pieces they’ve successfully finished in tumblers, resist the urge to try it for yourself. “Never do it with stones,” warns Hoch. “Even diamonds will break and chip running in steel. A lot of people do but grow to regret it. Just don’t do it.”
Sartin agrees, noting that he’s seen jewelers use rotary tumblers and steel shot to brighten up their pieces after setting. “I don’t agree with that,” he says. “The stones can damage themselves.” And under no circumstances should cut-down media be used with gem-set jewelry.
• Keep things clean. Jewelers who drop the ball on keeping their tumblers and media clean often start encountering black sludge on their pieces or may see their steel shot turn gray. This happens most often when using dirty water or just dish soap if the work is dirty when introduced into the tumbler. There are cleaning solutions available that can be run through the tumblers. But if time is of the essence, Hoch recommends a homegrown solution that works just as well: Take a can of Coca-Cola, let it go flat, and then pour it into the tumbler and run a cycle. “It will clean everything up,” she says. However, she notes that a better practice is to simply use clean liquid for each run or at least daily.
• Take good notes. Expect there to be some trial and error as you’re learning the process. Write everything down so you’ll know what did and didn’t work. Even after you’ve mastered the process, you’ll likely want to continue taking notes. Hoch keeps index cards taped to the wall near her tumblers. “When you start a run, note the time,” she says, as she often has multiple tumblers running at the same time.
• Practice makes perfect. Sartin says one of the questions they get asked the most is how long a finishing run is going to take. “We have no idea,” he says. “Different pieces have different geometries, different needs. It’s best whenever you get your equipment to start doing practice runs. Take the time to understand the equipment, the media, and write it all down. Once you know, it’s plug and play.”