Hole drilling is the most common operation performed on a vertical machining center. When this operation involves drilling deep holes, it becomes one of the most challenging. However, there are very effective ways to meet this challenge.
The goal is to produce these holes accurately, repeatably and with superior surface finish—and to do so economically.
The most important ingredient in successful deep-hole drilling is understanding. You have to understand what happens inside the hole as it is being drilled and how this knowledge guides your choice of the most effective techniques.
The Dynamics Of Deep-Hole Drilling
Strategies for deep-hole drilling address three primary issues: evacuating chips without damaging the surface finish, delivering coolant to keep the drill and workpiece material cool, and minimizing cycle time. Other important factors include accuracy, repeatability and surface finish.
Typically, a deep hole is defined by the ratio of the diameter to depth. Usually a ratio of 5:1 or greater is considered deep-hole drilling. For example, a 5-inch deep by 1-inch diameter hole is considered deep, as is a 0.125-inch diameter hole that is 1 inch deep.
Chips must be small enough to move up the tool’s flutes and out of the way. Long, stringy chips can damage surface finish and cause premature tool wear or breakage. Coolant has to get to the tool tip to keep the tool and workpiece cool, as well as force chips out of the hole. A rigid machine tool with good damping characteristics and low spindle runout is required to hit targets for accuracy, repeatability and surface finish. Of course, the right drill geometry will make deep-hole drilling operations much more efficient.
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