Striving for Consistency (continued) can be appropriate for holes less than 1.5 to 2 diameters deep, according to Ingersoll’s Jennings, who noted that the toolmaker offers standard tools to drill up to 8 diameters deep. Through-coolant is recommended for deeper holes to help evacuate the chips up the flutes and out of the hole. “With any production, high-feed drilling operation, through-the-tool coolant is certainly a requirement,” he said. Jennings added that the throughcoolant pressure should be at least 150 to 200 psi, but the best performances are achieved at around 1,000 psi. “If there’s a knob where you could turn the coolant pressure up,” he quipped, “you keep turning it until you take the bark off your hand.” “The more the merrier,” Hellinger concurred, adding that high-pressure coolant improves the hole’s surface finish, possibly eliminating a finishing operation. High-pressure coolant helps evacuate chips from the hole quicker and contributors Allied Machine & Engineering Corp. (800) 321-5537 www.alliedmachine.com reduces the possibility of having chips scour the ID. Additionally, the higher the coolant pressure, the less time the chip will reside in the drill flute. To avoid chips and particles being recycled through the coolant system and clogging a drill’s coolant holes, Sandvik Coromant’s Cole suggests filtering particles larger than 80 microns. “Maybe even 40 microns, depending on the size of the drill,” he said. Ductile Iron Society (440) 665-3686 www.ductile.org Guhring Inc. (800) 776-6170 www.guhring.com Ingersoll Cutting Tools (815) 387-6600 www.ingersoll-imc.com Sandvik Coromant Co. (800) 726-3845 www.coromant.sandvik.com/us Unimerco Inc. (734) 944-4433 www.unimerco.com Other Considerations A rigid setup is required when applying hard and relatively brittle carbide tools to drill ductile cast iron. “You need the right holders and of course you can’t have play or extra slop in the spindle,” said Unimerco’s Stead. He recommended hydraulic toolholders to minimize runout. Another option is shrink-fit holders. “Collets are not preferred,” Hellinger said. Guhring recommends hydraulic chucks or shrink-fit holders when possible to improve tool life and part quality. “The tool runout when measured at the point can be reduced to less than 0.005 microns, which is less than half of what can be expected of a collet chuck,” he said. “By reducing tool runout, tool wear is more consistent and accuracy improves.” The severe interruptions that sometimes go hand in hand with drilling through-cavities in near-net-shape cast
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