On the table: a guide to tabletop machines

A machine tool for serious, tight-tolerance work can come in a small package. Because tabletop—or benchtop or desktop—machines can be as small as a sewing machine, some people do not consider them suitable for commercial prototyping and microparts production. They may want to reconsider.

“We make our machines cost-effective, but [still provide] high precision in a small package to do small parts,” said Jerry Mraz, general manager for SmalTec International, Lisle, Ill. He noted that the machine builder’s Model 903 mill/grinder/polisher has a 100nm step resolution, and its Model GM703 EDM/grinder/polisher has a 10nm step resolution. “If we were to make that as a full-size unit, we’d be talking half a million dollars just to get the components.” (See chart for the cost of SmalTec’s machines and others.)

Mraz noted that the machine’s work envelope, which is essentially the machine’s three axes’ interface, is “very sound,” allowing the machine to operate properly on less-than-rigid structures.

On the small end of the tabletop scale are manual lathes made by Cowells Small Machine Tools. The smallest measures 420mm × 260mm × 343mm (17"×10½"×13½"). Colin Childs, director of the Colchester, England-based machine tool builder, defines a benchtop lathe as having up to 1,500mm (59") between centers. “Ours is 200mm between centers,” he said. “ ‘Tabletop lathe’ is probably a more accurate description of our machine because it’s cast with hand grips so you can pick it up, take it off the table and put it in a cupboard.”

Made with cast iron and steel components, the lathe weighs 55 lbs.—it’s three or four times heavier than similar-size machines—and is “as accurate as Swiss machines at about a tenth the price,” according to Childs.

On the other end of the scale is Atometric Inc.’s CNC mill, which is a self-contained, floor-mounted machine that measures 28"×29"×55" and weighs 890 lbs. “In a sense, the machine itself is small enough that it could be mounted on a tabletop,” said Thomas Lindem, president of the Rockford, Ill., company, noting that “compact” more appropriately describes the equipment. “I just think there’s something not serious about the term ‘tabletop.’ ”

Hobbyists welcome

Although the machines presented in the comparison chart on page 36 are accurate enough to produce parts with tolerances in the “tenths,” and often durable enough and suitable for high-volume production, it doesn’t mean hobbyists aren’t using them. According to Craig Libuse, marketing director for Sherline Products Inc., Vista, Calif., the company’s machines “are in the price range of a hobby machine,” ranging from $575 to $995 for a basic manual lathe or mill to less than $3,000 for a 4-axis CNC mill, including the computer. However, about half of the machines are sold for industrial purposes, such as medical prototyping. The Mini-Mill/GX desktop manufacturing system from Minitech Machinery has a granite base, and the drive mechanism consists of 15mm ballscrews and THK linear slides with caged-ball technology. Photo courtesy Minitech.

Of course, being a hobbyist, such as one involved in building and operating radio-controlled cars or planes, doesn’t disqualify someone from being a serious machinist.

“The guys who are winning [model-building] contests are the ones who make their own parts, which are lighter, stronger and better designed than the stock parts sold at hobby shops,” Libuse said. “It’s the guys at the very top of each hobby who we’re talking to.”

He added that a careful machinist can achieve accuracy of 0.0005" or better on a Sherline machine with a little care and good setups, but machinists usually hold tolerances consistently in the “tenths” ranges with grinding rather than machining, even on more expensive machines. “Our general claim is that with most good machine tools, including ours, you should expect to work to tolerances of 0.001",” Libuse said.

Rod Freeman, CNC technician for Cameron Micro Drill Presses, Sonora, Calif., said his company’s benchtop CNC machining centers could be used for industrial or hobby applications, too, as long as “the hobbyist has lots of money to throw around.”(Prices start at $43,000.) Though classified as a benchtop machine, Cameron’s 200-lb. machining center sits on a ground aluminum plate on top of a 3"×18"×24" block of ground granite that weighs about 100 lbs. In addition, the 100-lb. controller sits next to the machine. The machine isn’t attached to the plate or granite, enabling a user to move the machine and clean all surfaces.

Cameron also makes a rolling cart for mounting the machine. “You wouldn’t want to put it on a table unless the table had a bit of beef,” Freeman said.

For Minitech Machinery Corp.’s larger desktop manufacturing systems, such as its granite-base Mini-Mill/GX, the Norcross, Ga., machine builder recommends bolting them to a tabletop and offers provisions for doing so. Because a lot of small machines are used by hobbyists as well as for CNC and CAD/CAM training, Jack Heald, president and CEO of Minitech, noted that a desktop machine can have less-than-professional connotations.

Photo courtesy Sherline Products.

The CNC micromachining center-TC from Cameron Micro Drill Presses (below) with four-station toolchanger has a machine footprint of 18"×20" (460mm × 510mm). Billed as Sherline Products’ most popular mill, the Model 5400 milling machine (above) has a laser-engraved, 12" solid-aluminum base. F.W. Derbyshire offers microscale lathes (bottom) with a standard spindle speed of 5,000 rpm.

Photo courtesy Cameron Micro Drill Presses.

Photo courtesy F.W. Derbyshire.

“We, however, like to distinguish ourselves [by pointing out] that we’re above the hobby level, and we’re doing production work and serious machining with these machines,” he said, adding that the Mini-Mill/3 achieves an accuracy of 2µm to 3µm.

Array of applications

For Minitech machines, microscale production work includes medical, dental and microfluidic applications. “Jewelry is another big area,” Heald said.

Similar to the macroscale world, the list of industries using tabletop and other micromachining centers is virtually endless. “I’d be here all day listing uses for the machine,” said Cowells’ Childs, who mentioned watch making, cable work and aerospace parts among the applications.

Childs added that Cowells’ lathes are often used by professionals conducting research, as the machines are not designed for high-volume production. The design has remained the same during recent years as a result of being a “tried and tested product,” he said. “The machine does what it says on the tin.”

Mraz, on the other hand, noted that SmalTec has recently improved the sparking capability of its microEDMs to impart finer surface finishes, produce sharper corners and achieve tighter tolerances. The sparking capability improvement has allowed the equipment to make further inroads in industries requiring precise, small holes, such as those for diesel fuel injectors and inkjet nozzles. “About 90 percent are being made with our technology,” he said about the latter components.

Small isn’t synonymous with delicate for micromachining centers. Some SmalTec machines regularly produce thousands of parts a month, Mraz noted. “We’ve been around since 2002, and I generally make one service call per year on all the units we have installed,” he said. Photos courtesy Cowells Small Machine Tools.

Cowells Small Machine Tools’ 90CW lathe (above) is accurate to within 0.005mm (0.0002") and accepts 8mm horological collets in both headstock and tailstock spindles. The 90ME screw-cutting center lathe (below) from Cowells Small Machine Tools has back gearing for low-speed, high-torque machining.

Scaling down

According to Libuse, users can perform some low- to medium-volume production runs more economically on Sherline machines than more-expensive units because Sherline’s replacement components are relatively inexpensive. For example, a lead screw for the mill is $18, and the nuts that drive the lead screws are $2.40 apiece.

“If you go through a headstock every 6 months, it’s about $100,” he said. That’s the case for end users running the machines up to 10 hours a day. “They just buy an extra headstock and when it wears out, they send it back to us for new bearings and put the other headstock in,” Libuse added.

Not only are tabletop machine components less expensive than their macroscale counterparts, but the time and expense to change components is considerably less, noted Cameron’s Freeman. “End users can do their own maintenance, or we go there and service the machine,” he said, adding that the components that wear include spindles and lead screws. If need be, the machines are small enough to crate and ship to Cameron for refurbishing.

In addition to the basic components, some micromachine builders offer an array of accessories. For example, Sherline offers more than 150 accessories, including rotary tables, boring heads, machine vises and tilting angle tables. “Everything that goes with a machine shop in miniature,” Libuse said. “Because our machine is small and fairly unique, we had to manufacture the entire line.”

Other builders’ offerings are more limited. “We like to sell the functional system right out of the box,” said Mraz.

When shopping for a micromachine, Cowells’ Childs pointed out that end users need to determine if a machine is large enough for what they intend to do, and if it’s able to achieve the required part tolerances.

If a tabletop micromachining center meets the requirements, selecting one instead of a larger offering is a no-brainer. “If two machines have equal performance,” asked Atometric’s Lindem, “why would you want one that takes up 10 times the work volume and consumes four times the utilities?” µ

About the author: Alan Richter is a senior editor of MICROmanufacturing. Telephone: (847) 714-0175. E-mail: alanr@jwr.com.

Contributors

Atometric Inc.
(815) 986-7352
www.atometric.com

Cameron Micro Drill Presses
(209) 532-7201
www.cameronmicrodrillpress.com

Cowells Small Machine Tools
+44 1206 251792
www.cowells.com

Minitech Machinery Corp.
(800) 662-1760
www.minitech.com

Sherline Products Inc.
(800) 541-0735
www.sherline.com

SmalTec International
(630) 364-1788
www.smaltec.com