Modern Machine Shop

JAN 2018

Modern Machine Shop is focused on all aspects of metalworking technology - Providing the new product technologies; process solutions; supplier listings; business management; networking; and event information that companies need to be competitive.

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MMS JANUARY 2018 60 CUTTING TOOLS of vibrations during machining. This does not stop the vibration, but rather stops the knocking caused by out-of- sync vibrations. Apparently, when the knocking goes away, so do the other unwanted side effects. Mike MacArthur, vice president of engineering at RobbJack, explains that the end mill design includes a special edge preparation that creates an additional surface along the trailing side of each spiraled f lute. The company calls this additional feature the Mirror Edge, because it is highly polished and shiny. This added edge is 0.001- to 0.002-inch wide, so it can barely be discerned by holding the tool and slightly turning it in the light. The photo above captures the slender band of light ref lected by this edge as Getting an Edge on Chatter Control This end mill design enables it to vibrate at the same frequency as the workpiece, preventing vibration from turning into chatter. MARK ALBERT | EDITORIAL DIRECTOR In a machining process, vibration causes chatter. More specifically, chatter occurs when the workpiece and the cutting tool are vibrating at different frequencies. Literally, the workpiece is moving in one direction while the cutting tool is moving in the other direction. Of course, these relative motions are slight and happen at many times a second. Chatter is the resultant sound of the workpiece and the cutting tool knocking into one another at a high rate. This knocking does more than make an irritating noise: It also damages the tool, degrades the workpiece surface, harms the machine's spindle and may leave part features out of tolerance. Cutting tool manufacturer RobbJack has a strategy for dealing with chatter that is based on the concept of getting the cutting tool and the workpiece to vibrate in the same direction at the same rate. To this end, the company has devel- oped an end mill design (primarily for milling aluminum at high feed rates) that gets the cutter and the workpiece to synchronize the frequency According to RobbJack, the Mirror Edge feature helps stabilize the end mill's contact with the workpiece surface to synchronize the vibration of the cutting tool and the workpiece. MIRROR EDGE

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