Tooling and equipment strategies for getting the most out of your Swiss-style lathe
So you’ve heard all sorts of good things about Swiss-style, sliding headstock CNC lathes and have been thinking about investing in one. There are some excellent reasons to do precisely that. With five-axis milling capabilities, multiple tools in the cut at once, and much faster spindle speeds than are possible on conventional, fixed-headstock lathes, these versatile machines can be thought of as the Swiss Army knife of the machining world, able to machine a variety of round and some not-so-round parts in a single operation.
Then again, you may already have one of these wonder machines on the floor and are wondering what’s so wonderful about it. The setup times are long. You can’t find an operator. The programming is difficult.
And just last week, there was a crash—not enough to seriously damage one of the most expensive machines in the shop, but enough to cause a day of downtime and inflict a hefty repair bill. That money could have been better spent on additional operator training for a machine tool that even Swiss experts admit can be intimidating.
Stop The Turnover
Training is crucial, not only to the elimination of these problems, but to fully realizing a Swiss CNC’s full potential. Because of this, Phillip Judt, applications engineer at Absolute Machine Tools Inc., Lorain, Ohio, suggested that shops set aside sufficient training dollars as part of any new machine purchase, and then make sure that the Jedi Knights emerging from these classes stick around to justify the investment.
“Some shop owners think that machine operators are plug-and-play, and while that’s not usually the case with any CNC machine tool, it’s especially not true with Swiss-style machines,“ he said. “Here, it’s a different way of thinking. When most everything moves in every direction, it can be difficult to establish a fixed point of reference like you have with a conventional lathe. That’s why I tell customers to start with one tool—some like to use the cutoff, while others (I’m one of these) use the facing tool—and always keep that as the zero point from which to set all the other tools.“
Once this technique has been established, he added, everyone who operates that machine or any of the shop’s other Swiss-style CNCs (they tend to multiply after the first one) should set their tools in the same manner. Doing so eliminates errors and reduces the likelihood of a crash, while also saving precious minutes of setup time. Further, these sorts of standardized procedures help to reduce employee contention and confusion, morale killers that so often send valuable employees to the shop down the street.
New Ways of Tooling Up
Part of this training centers around different kinds of tooling. Here again, significant differences exist between the cutting tools and toolholders used on a Swiss machine and those of a conventional, turret-style CNC lathe, never mind the fact that many of the former are as much milling machine as they are lathe. Determining what works and what doesn’t requires that programmers and operators have the time needed to experiment with smaller, sharper Swiss-style turning inserts as well as end mills and other rotary cutters that might be less familiar to a lathe machinist.
It’s for this reason that Judt and others interviewed for this article agreed that it’s a good idea to lean on the machine distributor’s applications engineers for advice—especially when just getting started—and always keep the front door open to knowledgeable cutting tool salespeople. “Yes, you should be selective on how many hours you spend each month evaluating new tooling, but at the same time, it pays to be aware of what’s out there and how to best apply it,“ he said.
One of the things these folks might suggest is quick-change tooling. Derek Briggs, Swiss product manager for Tsugami/Rem Sales LLC, Windsor, Conn., noted that changeover time is a killer for many shops. The best way to combat it is to invest in a system that provides for offline measurement and allows individual tools or even an entire gang plate to be swapped out in seconds.
“For shops that are running high production volumes, quick-change eliminates the need to reach into the machine, where quarters are typically tight,” he said. “And for lower-volume shops that may be setting up several jobs a day, quick-change is even more crucial. You can get all of your tools ready, undo one screw, replace the toolholder or live-tool assembly, and move on to the next tool in the setup. In either environment, it’s a huge timesaver.”
Swiss Teams up with Laser
Despite the higher training costs and learning curve associated with Swiss-style CNC lathes, shops should strive to stay abreast of their equipment’s capabilities. Machine builders continue to add new features and control functions that make their wares easier to operate and more versatile, and many of these can be retrofitted in the field. Advances include “superimposition” cycles that facilitate the multiple-tools-in-the-cut capability mentioned earlier, as well as numerous automation and metrology options, user-friendly programming packages, and the ability to break even the gnarliest of chips.
Consider this last option. Chip control can be problematic in any turning application, but particularly in a Swiss-style machine with its relatively small work zone and dozens of tools that can grab onto a passing wad of chips. Because of this, virtually all Swiss-style machine builders now offer a way to “oscillate” or “vibrate” the turning tool while in the cut, moving it back and forth just enough to break stainless steel and even super-stringy Teflon into manageable pieces. That’s good news, but perhaps the best aspect of this feature is that it’s often available through a simple software update or modification to the control’s ladder diagram.
This is just one of the Swiss industry’s game-changing technology developments over recent years. Another is the use of lasers. Tsugami and Citizen, for example, are among the growing number of Swiss-style machines that offer integrated fiber-optic cutting and welding lasers on select machine models. Rich Miller, North Central regional sales manager for Marubeni Citizen-Cincom Inc., Allendale, N.J., said the company’s latest laser unit can adjust beam focus, assist gases, and gas pressure, all on the fly. “This allows our users to make custom ‘recipes,’ if you will, that can be called up at any time to cut or weld different materials and thicknesses in the same machine cycle.”
Another novel option—at least for some Swiss models—is an automatic tool changer (ATC), a feature that brings these machines into larger, fixed-headstock multitasking lathe territory. Miller noted that, while Swiss-style machines are typically generous in terms of fixed tool stations, operators often find themselves short on rotary tools. Citizen has solved this problem by offering a 13-tool ATC option for its L20-XII B-axis machines that “can be added many years later,” Miller said. Several other machine builders offer similar options, at least some of which can be installed in the field.
Blurring the Line Between Fixed and Sliding
This last feature illustrates an industry-wide blurring of the line between fixed- and sliding-headstock machines, and even between lathes and machining centers. Rem Sales’ Derek Briggs suggested that many of today’s Swiss-style CNC lathes are more like a five-axis machining center, one where the vise is the spindle, and dozens or possibly hundreds of parts can be machined without operator intervention.
“Shops need to think outside the box when they enter Swiss territory,” he said. “We see customers every day that are making bone plates and other non-round parts on machines like our Tsugami SS38MH-5AX. You can run square or hex stock, extruded materials, and because most machine builders now offer convertible spindles—where the machine can be used as a chucker—you can also load sawed and cold-headed blanks. The point here is that, unlike previous generations of Swiss-style lathes, not everything has to be machined from a twelve-foot bar of round stock.”
Ed Garber, national sales manager at Star CNC Machine Tool Corp., Roslyn Heights, N.Y., agreed, noting that the parts in his tackle box of sample parts have changed over the past five years. “It used to be that most everything I showed to customers had long length-to-diameter ratios, and most were relatively small—screws and pins and actuator rods, that sort of thing,” he said. “Now, the parts are larger, more complex, and definitely not the long, skinny parts that Swiss machines are known for. And because these machines are capable of turning and milling a complete part in a single operation, most of them are more accurate as well.”
Rise of the Robots
The convertible main spindles that are now practically standard equipment on Swiss-style CNCs raise another possibility beyond the chucking of larger parts. They also open the door to robotic part handling, something that most experts agree is on the rise with Swiss-style and conventional turning machines alike. One example of this comes from Index Corp., Noblesville, Ind., where Proposals Engineer Randy Carlisle has been kept busy of late writing proposals for the company’s recently introduced iXcenter integrated robot cell.
Carlisle said the self-contained system is equipped with a six-axis robot, custom end-of-arm tooling, and palletized part storage. It is designed for the loading and unloading of Index’s TNL-series machines, he explained, but can also be used in conjunction with a CMM or comparator-style gaging. “It allows you to pull a workpiece out of the spindle, place it into a Renishaw Equator, for example, inspect it, and either place it into a tray or call for an operator if there’s a problem.”
Faster and Faster
As noted previously, the five-axis milling capability of Swiss-style lathes is making them increasingly attractive to shops looking for ways to complete parts in a single operation. And because most of these parts are relatively small (most Swiss-style machines have a maximum bar capacity of 32-38 mm, although a few boast 65 mm or more), the cutting tools used to mill these parts are similarly small, thus requiring higher spindle speeds. Index Applications Engineer Gonzalo Serrano pointed to the company’s new 55,000-rpm, coolant-driven live tools as one high-speed rotary tool solution. Other machine builders offer pneumatic live spindles with comparable speeds or servo-powered rotary tools able to achieve 20,000-rpm or more.
Granted, high spindle speeds are the norm in Swiss-land, which is one reason why a high-quality bar feeder should be used whenever possible. They serve to dampen the inevitable vibration that comes when a 12' (3.66-m) bar of material is made to spin at 8,000 rpm or more, and if unattended machining is the goal, a high-end magazine-style feeder can keep even the hungriest of CNC lathes fed throughout the night. If your shop decides to save some cash with a general-purpose bar feeder, investing in one able to sustain the extreme spindle speeds possible on most Swiss lathes is a sure way to increase throughput and part quality.
While you’re at it, take a hard look at the bar-feeder-to-machine interface. “We’ve done a lot of work recently with end-of-bar signaling, which helps shops maximize their material usage,” said Star CNC’s Garber. “If you’re down to the last ten inches or so and don’t have enough material left to complete the current workpiece, we have macros that will call up a different, shorter part that uses the same material, thus minimizing the bar remnant. Knowing exactly when you’re going to run out of material also helps with scheduling, and is critical for unattended machining. To this last point, we’ve also released SMOOSS-i (Star Monitoring and Operator Support System), a software system for remote monitoring and data collection.”
The Call for Good Code
The list goes on. Swiss-style machine tool builders continue to improve their guide bushings, largely eliminating one common gripe among machine owners: the need for centerless-ground bar stock. Most also offer some level of programming assist and simulation capabilities, easing the specter of managing three or four simultaneous operations. In-machine probing systems are beginning to pop up, thread whirling is becoming more common, and machine tools overall are growing faster and more accurate, boasting additional cutting tool stations. The takeaway? Although there are many ways to improve the efficiency of existing Swiss-style CNC equipment, it could also be time for an upgrade.
Which brings us to the final point: programming. As just mentioned, many Swiss-style machines come equipped with on-board or sometimes stand-alone programming and simulation tools. Still, it’s important to note that these are most suitable for simpler parts and toolpaths, and not widely considered to be “full-blown” CAM systems. That’s according to Chris Leclerc, Swiss product specialist at Mastercam developer CNC Software Inc., Tolland, Conn., who offered many good reasons to use his company’s programming software, starting with its flexibility.
“The programming aids that come with many machine tools are perfectly fine for setting up a threading cycle or validating your synch codes, but they have certain limitations,” he said. “This isn’t meant to disparage those systems, as they’re a good starting point for many shops, but a true CAM system like Mastercam provides capabilities that are needed for maximum machine utilization.”
CAM software, he explained, supports wireframe and solid part models. It offers tooling libraries, turning and milling strategies, and it simplifies one of the more challenging aspects of Swiss-style programming—the synchronization and superimposition functions mentioned at the start of this article, functions that are responsible for a Swiss-style CNC’s ability to produce parts three to four times faster than conventional lathes.
As for the programming itself, Leclerc suggested it’s not all that difficult, even for those who’ve been programming two-axis lathes for decades. “In a CAM system, you program a Swiss machine exactly like you’ve been programming your other lathes and machining centers. The software takes care of switching the axis directions, the G and M codes, the wait commands, the turning, drilling, and milling operations, and it shows you how it’s all going to work in the machine. When everything is the way you want it, the post-processor stitches it all together and generates accurate G-code. That’s all there is to it.”