b'\x1b\x1a\x19 \x1f\x18\x1d\x17\x16Shop OperationsHACKING CHATTERBy Kip Hanson terial is never the same, Palmierimodified tool shank, like the Helical said. This actual amount of fluteSolutions ToughGRIP shank. It offers M achineshopsgotogreatspacing is more a factor of endmilla higher coefficient of friction, com-lengths to eliminate chatter.size rather than the material its de- pared to a polished carbide shank, Dan Maloney, one of the writ- signed for, however. A similar phe- and eliminates any chance of move-ers of the blog Hackaday (www. nomenon occurs with variable-helixment within the holder.hackaday.com), even went so far asendmill geometry, where changingIts also important to consider the to modify the electronic drive unitthe angle slightly from flute to flutetoolpath. For harmonics to occur, on his engine lathe to automaticallylikewise serves to reduce chatter. cutting forces have to be in sync, oscillate the spindle speed in hopesPalmieri explained that, in eitherhe said. The spiral cutting paths of breaking up vibration. Maloneyscase, the geometry must also beused with trochoidal and other high-approachattaching a 555 timerbased on the workpiece material efficiency programming methods board that drives a relay to toggle the IO pins on and offwas some-what successful, but its not practical for CNC equipment. Also, his statement that vibra-tion is a fact of life in almost every machining operation is question-able. Perhaps hes right, but if you cant hear it, who cares? Still, when chatter does rear its ugly head, something must be done. Before breaking out the solderingHarvey Performanceiron and a 555 timer, its a good ideaA sampling of the many variable-helix endmills available to manufacturers.to look at your cutting tools. Another blog, this one from Har- increasing the helix angle to allowcause cutting forces to be exerted vey Performance Co. LLC, Rowley,for the aggressive feed rates usedin different directions as the tool Mass., suggests that material-spe- when cutting nonferrous metals, formakes its way into and out of the cific cutting tools are part of theinstance. Thats why its important toworkpiece. This does reduce vibra-answer. choose a cutter specifically designedtion somewhat, but its still a good For example, Chris Palmieri, pro- for your machining application, es- idea to use a variable-pitch, variable-duction development engineer atpecially where chatter is an issue. helix tool to ensure that chatter is Harvey Performance, said the ge- Palmieri said increased tool ri- minimized as much as possible.ometry of an endmill designed forgidity, tool balancing and minimalSeco Tools LLC, Troy, Mich., re-stainless steel differs from one usedrunout also contribute to chatterfers to this type of chatter reduction to machine aluminum. However, thereduction. He recommends using aas passive, in that proper machine same basic approach to chatter re- construction, tool selection and, to duction applies in either instance a lesser extent, part design can go a namely, varying the flute spacingKip Hanson is along way toward eliminating chatter. contributing editor and helix angles to break up thefor CTE. ContactWhen thats not enough, dynamic harmonics that lead to chatter.him at (520) 548- vibration control must be applied.A variable-pitch tool assures that7328 or khanson@ Thatsaccordingtoarecent the time interval between two suc- jwr.com. whitepaperbySecoProduct cessive flutes contacting the ma- Manager Pierre Zunino and R&D 28MARCH 2018ShopOps.indd 28 2/14/18 3:18 PM'