Walk into most any machine shop and there’s a good chance you’ll hear it: the high pitch whine of a deep boring operation, the chatter loud enough to have even the most hard of hearing among us scrambling for a pair of ear plugs. It’s a problem that has plagued machinists since the day lathe inventor Henry Maudslay first chucked up a piece of steel and tried to bore a hole through it, and has only gotten worse as metals have grown tougher and more challenging to machine.
Not anymore. Kennametal’s latest weapon in the war on chatter is one that will have machinists everywhere saying, “I need that.” The new boring system boasts the most effective antichatter mechanism ever developed by Kennametal, and also offers an extensive range of indexable heads and shank sizes.
Someone who knows all about it is Sam Eichelberger, product engineer for lathe systems engineering and part of the team that developed the internal dampening mechanism. “Perhaps the most important thing to know about the new bar is that it’s plug and play,” he says. “There's no need whatsoever for tuning or adjustments—you simply pull it out of the package, mount it in the turret and get boring.”
There’s more to the story than making the shop a quieter place to work, however. Eliminating vibration and therefore chatter greatly extends tool life, never mind its positive effect on part surface finish. And when tools last longer, they can be pushed harder, with feed rates, cutting speeds and depths of cut many industry experts once thought unachievable.
Eichelberger is one of them. He lists a number of features that not only make the vibration-free boring system easy to apply, but also productive. These include a serrated, bolt-on connection at the bar’s business end that securely clamps a variety of styles and sizes of indexable heads.
Better yet, the heads themselves have been put on a diet, with a shorter length and lighter weight that provides greater stability, contributing to the bar’s improved performance. They’re also coolant-fed, to precisely direct a stream of high-pressure coolant where it’s needed most. The result is hassle-free chip control together with maximum cooling in the cutting zone.
Most important of all is the internal dampener. Said Eichelberger, “The bars are both vibration and maintenance free. Within the bar there sits a mass that's supported by a pair of elastic supports, inside of which sits a dampening fluid. This mass vibrates at a predetermined frequency during machining, attenuating the natural frequency of the bar around it to suppress vibration. There are no wear components to worry about, nor tuning—as Sam mentioned, you just set it and forget it.”
The vibration-free system offers superior performance in boring applications up to 10 diameters deep, Eichelberger explained, much deeper than solid carbide or heavy metal boring bars are capable of. Internal and customer test results show surface finishes as good or in most cases better than competitive “quiet bars,” with significantly more aggressive cutting parameters possible across the board.
Of course, boring bars are only as good as the method by which they’re clamped in the machine. Kennametal has addressed this critical consideration by supplying machine-specific turret adapters, along with a special split sleeve bushing for maximum rigidity. “That’s the goal of this product,” says Kennametal global product manager John Gable. “The greatest stability possible and the most effective dampening solution available, period.”
Anyone who’s ever struggled to get a boring bar exactly on center will appreciate that setup is extremely easy. “There’s a reference flat on the top of the head that accommodates a visual angle finder,” Eichelberger pointed out. “You just rotate the bar until the indicator reads zero, then clamp it in place.”
Considering the higher cost of a such a boring system, they’ll also appreciate that the heads are replaceable in the event of a crash, avoiding damage to the bar itself. And users of Kennametal’s older boring system will find that their new heads fit perfectly with the use of an adaptor.
“The portfolio for our Imperial bars ranges from one-inch in diameter up to four inches, while the metric version starts at 25 mm and goes to 100 mm,” Gable said. “There are a variety of interchangeable head styles available as well, everything from screw-on positive rake inserts for fine-finishing needs to negative rake, clamp-style geometries for heavy roughing. The bar’s designed to excel in demanding applications, and that’s exactly what it does.”
Related Glossary Terms
Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.
- boring bar
Essentially a cantilever beam that holds one or more cutting tools in position during a boring operation. Can be held stationary and moved axially while the workpiece revolves around it, or revolved and moved axially while the workpiece is held stationary, or a combination of these actions. Installed on milling, drilling and boring machines, as well as lathes and machining centers.
Cylindrical sleeve, typically made from high-grade tool steel, inserted into a jig fixture to guide cutting tools. There are three main types: renewable, used in liners that in turn are installed in the jig; press-fit, installed directly in the jig for short production runs; and liner (or master), installed permanently in a jig to receive renewable bushing.
Condition of vibration involving the machine, workpiece and cutting tool. Once this condition arises, it is often self-sustaining until the problem is corrected. Chatter can be identified when lines or grooves appear at regular intervals in the workpiece. These lines or grooves are caused by the teeth of the cutter as they vibrate in and out of the workpiece and their spacing depends on the frequency of vibration.
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
- flat ( screw flat)
flat ( screw flat)
Flat surface machined into the shank of a cutting tool for enhanced holding of the tool.
Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.
1. On a saw blade, the number of teeth per inch. 2. In threading, the number of threads per inch.
Angle of inclination between the face of the cutting tool and the workpiece. If the face of the tool lies in a plane through the axis of the workpiece, the tool is said to have a neutral, or zero, rake. If the inclination of the tool face makes the cutting edge more acute than when the rake angle is zero, the rake is positive. If the inclination of the tool face makes the cutting edge less acute or more blunt than when the rake angle is zero, the rake is negative.
Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.