by Kip Hanson
Deep boring doesn’t have to be difficult…or noisy
Boring is one of the more challenging of turning operations. Even with a solid carbide boring bar, get much beyond a 6:1 overhang and chatter begins to rear its ugly head. Poor surface finish is assured, as is rotten tool life, accuracy problems, and enough racket to have everyone in the shop wondering about the price of hearing aids.
You might try tipping the bar above centre a bit. Wrapping the shank in a brass, aluminum, or lead sleeve can have a positive effect. So-called heavy metal bars are another approach, although these are less rigid than carbide, despite their damping effect. Feeding faster helps at times, as does slowing the spindle, but the fact remains that, quite often, none of these things help and deep bores are a real pain in the neck.
So long, carbide
A number of cutting tool suppliers recognize this problem and have brought their own unique technology to bear. Each of the following solutions is said to reduce or eliminate chatter in hole depths up to 10xD, sometimes deeper. Each uses a proprietary anti-vibration mechanism within the boring bar shank. And each is fairly expensive compared to the steel or carbide bar you’re currently using. As you’ll see, however, the investment is likely an easy pill to swallow.
Quiet Like a Whisper: Iscar Tools, for example, offers its WhisperLine brand of deep boring tools, introduced in 2017. As product manager Ashok Guruswamy explains, carbide tools can be used safely up to 7xD, heavy metal bars are good to 8xD, but beyond that, issues with tool life, hole accuracy, and surface finish begin to crop up. “There is a huge demand for this product, not just for applications that require better surface finishes and size control, but for greater productivity,” he says. “With anti-vibration bars, there’s no longer a need to compromise on speeds and feeds, and chip control becomes much more manageable as well.”
Plug and Play: Kennametal has a solution called Vibration Free that’s being introduced at IMTS 2018. Sam Eichelberger, product engineer for lathe systems engineering, is a member of the team that developed the internal damping mechanism. “The damping mechanism is a mass that’s supported by a pair of elastic supports within the bar, which vibrate at a predetermined frequency to attenuate the first mode of natural frequency of the bar and suppress any vibration,” he says. “The material that you’re cutting has no effect on the bar’s performance and there are no
wear components to worry about—you can just stick it in the
machine and go.”
Silence is Golden: Sandvik Coromant’s Silent Tools have been around for more than four decades, says product specialist Kevin Burton. The damping mechanism was developed and patented in 1967 by an engineer working at Teeness, a nail manufacturer in Sweden. Sandvik Coromant partnered with the company, and eventually purchased them outright. Since then, the Silent Tool line has expanded beyond deep hole boring to include milling cutters, and the company is in the process of releasing its Bluetooth-capable CoroPlus bars with remote setup and monitoring capabilities. “There’s also our -4C series, which we designed specifically for applications where cutting forces are high, such as threading and grooving,” says Burton.
Stay steady: Last but not least, Seco Tools has developed its Steadyline system for stationary and rotary applications, which uses “dynamic passive” technology to stop chatter in its tracks. “It works much like the active dampening systems used to reduce structural sway in tall buildings during earthquakes,” says Aaron-Michael B. Eller, product manager for ISO turning and advanced materials at Seco Tools, LLC. “Inside each Steadyline tool body sits a dense plastic-like material that moves back and forth slightly to counteract the vibrations encountered during deep boring operations, completely eliminating them.”
If you’re thinking these sound like a bunch of me-too products, not so fast. Each solution has its merits, and each company has put significant work into developing the best technology possible. It’s up to the end user to evaluate which works best for their applications, hopefully with the support of a knowledgeable support person.
Exploring the merits
Unlike older boring systems that need to be tuned based on length and material, this new generation of “quiet” bars come pre-tuned; there’s no adjustment needed. Some have ends that can be trimmed slightly, but for the most part they should be left as is, so as to avoid damaging the internal mechanism. “If you see fluid leaking out the end, you know you went too far,” laughs Eichelberger.
Each of these systems offers replaceable heads. Coolant through is common, and should be used whenever possible. Some support depths up to 14xD. Steel, carbide, and carbide-reinforced versions are available. Bar sizes range from 16 mm (0.63 in.) to ones larger than a redwood—Sandvik Coromant’s Burton mentions a bar one-metre in diameter (39.3 in.) and roughly 10 m long, used to cut bores for cargo ship drive shafts.
Nor are they limited to boring. Grooving and threading are also common applications, and as already mentioned, anti-vibration bars are routinely used for milling deep pockets and tall shoulders, especially with nickel-based alloys and other challenging materials.
Without such a device, vibration spreads through the tool holder and beyond, causing problems with surface finish and tool life. But it’s the productivity gains that may best justify the relatively high cost of these systems—everyone agrees that higher feedrates and faster spindle speeds are possible when the bar isn’t squealing like a hurt animal.
There’s no reason to wait for the squealing to start, however. Great productivity increases and surface quality improvements are possible even for overhangs as short as 4xD, making these bars valuable contributors to virtually any boring operation. “We’ve seen feedrates of 0.2 mm/rev (0.008 ipr) and surface speeds of 200 m/min (650 sfm) in 4140 and 13-8 PH with no problems whatsoever,” says Guruswamy.
Setup is easy. Each manufacturer provides reference flats or an electronic leveling device to help the operator achieve perfect centreline. “We’ve had some people set them above centre because they’re trying to compensate for deflection, but we recommend that you set them exactly on centre,” says Burton.
Everyone also agrees that the method by which these boring bars are mounted is equally important; a split sleeve is highly recommended to avoid the bell-mouthing that may otherwise occur when using two or three set-screws to clamp boring bars in place.
“These bars are quite popular with oil and gas, automotive, aerospace, and pretty much anyone that does a lot of boring,” says Seco’s Eller. “Those who’ve invested in one quickly recognize the value when the application is done in half the time and they’re able to get the parts out the door much faster. Higher quality parts with better surface finish, more repeatability, and reliability in the tool—compared to the struggles associated with standard tooling, anti-vibration bars make good sense.” SMT