- April 28, 2019
Multidirectional turning and grooving tools save time, improve tool life and reduce operating costs
The turret doesn’t have enough stations. The cycle time is too long. Chip control and surface finish are awful. Whatever the reason, lathe operators are often faced with the need to make tools do double duty, and whether that means using an indexable insert drill for some rough boring or a groover as a cutoff tool, machinists have long been known for their ability to do more with less, even when those solutions fly in the face of so-called traditional machining practices.
That’s just fine with Ashok Guruswamy, who says this type of unconventional thinking should be embraced rather than avoided. As the product manager for Grip/Turn products at Iscar Tools Canada, he can recommend any number of ways to do exactly that, eliminating these and other problems by using tools designed specifically for multidirectional turning.
These switch hitters include the Penta 17 for back turning and parting operations on Swiss-style turning machines, the Dove-IQ-Grip and Sumo-Grip for grooving and turning in heavy industry applications, and the DR-MF, a round shank, multifunction tool able to turn, bore and groove internal and external part features alike.
“The basic principle behind multidirectional turning is the deflection of the cutting tool, which creates a small amount of clearance between the workpiece and the insert face,” says Guruswamy. “This amount of deflection is influenced by a number of factors such as feed rate, cutting speed, depth of cut, insert width to overhang ratio, and of course the workpiece material, but when properly dialed in, a high degree of accuracy up to +/- 0.010 mm [+/- 0.0004 in.] can be achieved in many turning operations.”
Guruswamy agrees with the list of problems listed earlier, but adds that proper application of a multidirectional turning strategy often results in improved surface finishes “with no mismatches” and productivity increases of 25 per cent. And because some groove/turn tools offer up to five cutting edges per insert, tool costs are reduced as well. “Just be sure to use the feed and speed recommendations that come with the insert, otherwise problems such as poor chip control or vibration and chatter may occur,” he says.
Sorting through systems
One multidirectional trick suggested by Guruswamy and others is using a groove/turn tool to bore in the Z-positive, opposite the conventional direction. Edwin Tonne, training and technical specialist at Horn USA Inc., says this approach leaves more room for chips and provides a more stable cut.
“This is especially helpful with very small boring operations on Swiss-style CNC lathes,” he says. “For example, we have customers using our Supermini system to bore holes down to 0.2 mm [0.008 in.] in diameter—it’s obvious that you need as rigid a tool as possible in applications like these, and that any amount of chip packing will cause problems.”
The Supermini accepts more than 1,000 grooving, back-boring, profiling and threading inserts, Tonne says, all in the same holder. If that’s not enough, Horn offers a slightly larger system—the Mini—as well as dozens of distinct grooving and turning systems, each with their own assortment of specialty inserts and many able to cut in multiple directions.
Why so many? Tonne says it’s for greater stability. “With small turning, every millimetre of overhang counts, so you need a variety of holders, insert sizes and lengths to maximize stability,” he says. “Also, many Swiss machines have a limited number of tool stations, so you also need tools able to perform multiple operations.”
For example, Horn’s K and KF geometries have a round profile and can be used for internal or external contouring. And the 105 Series of Supermini is “widely used” for grooving and side turning. “When you get into multidirectional turning at these diameters, you need tool geometries that are optimized for the materials being cut, that can manage the chip correctly and minimize the cutting forces to achieve the best tool life and part quality possible,” Tonne explains. “That’s why we offer so many choices.”
For larger parts, call Don Halas, product manager for threading and grooving API at Seco Tools LLC. He’ll explain the many benefits of his MDT (multidirectional turning and grooving) system. “You keep the insert in the cut,” he says. “When you do that, you reduce tool changes and turret positioning moves, which equates to shorter cycle times, more widgets out the door, more money in the shop’s bank account.”
It also makes for nicer looking parts. As Iscar’s Guruswamy noted, multidirectional turning systems generate better surface finishes—Halas says this is due to the wiper effect that comes with any properly applied groove-turn insert. “Compared to a standard CNMG-style insert, it’s possible to cut surface roughness in half using a multidirectional tool,” he says. “Or you could just leave the surface finish the same and feed the heck out of it.”
This is an important point. Halas says the serrated locking mechanism on Seco Tools’ MDT system can withstand feed rates up to 30 per cent higher than competing solutions. Unfortunately, many machinists under-feed their tools, multidirectional or not, thereby missing out on substantial productivity gains. “It’s gotten better over the past few years, but I still come across a lot of shops that use the wrong cutting parameters, whether it’s on our tools or someone else’s. Always stick to the manufacturer’s recommendations, and don’t be afraid to ask them for help if you run into problems.”
Programming is another important consideration with multidirectional turning. Depending on the cutting tool, the material, and the part geometry, the standard grooving and turning cycles from most control manufacturers will not support the zig-zag or staircase toolpaths needed for many applications. The good news, at least according to everyone interviewed for this article, is that most CAM systems make short work of what was once considered a newfangled turning process.
But when tools can cut in any direction with equal aplomb, how does a machinist know when to turn, and when to groove? Good question, says Halas. “If the groove is wider than it is deep, side turning will almost always be faster than plunging. Chip control will be better, and because you’re generally taking lighter depths of cut, cutting forces are reduced as well. Like I said earlier, multidirectional turning offers a number of benefits, but they all come down to one thing: more parts on the table at the end of the day.” SMT