What are the requirements for high-speed drilling?

One of the most important requirements for high-speed drilling is also one of the most basic. Any skilled machinist knows to check for concentricity errors or runout of the cutting edge of a drill. As speeds increase, bit centerline alignment becomes more critical. A key reason has to do with tool materials. At lower speeds, shops can drill efficiently with tools made of high-speed steel, which has relatively high toughness and flexural strength.

However, higher speed applications require cemented carbide, or possibly ceramics – both of which sacrifice some toughness in favor of wear and heat resistance at higher cutting speeds. Evenly distributed cutting forces from low runout are critical to achieving acceptable tool life with these brittle materials, especially as spindle speeds are pushed into the five-figure range.

An effective process drilling at this rate should have no more than 20 microns of total runout. This error is measured after the drill is loaded into the toolholder and spindle and is the sum of the runout of the four components of the process: machine spindle + spindle/toolholder interface + toolholder/tool interface + the tool itself. If a shop is drilling at high speeds with existing machines and has no plans to change spindles, the first two factors that lead to errors are out of control.

However, none of these are the most significant sources of jitter on relatively new machines. The spindles supplied with most of today's machine tools, even the relatively inexpensive ones, typically offer concentricity and toolholder position tolerances that allow enough room in the 20 micron margin. It is also very unlikely that the drill itself caused the error. Today's cutting tools are being manufactured to tighter and tighter concentricity tolerances.

This makes the tool holder fixture the most significant source of runout. In fact, the wrong toolholder itself can cause errors of more than 20 microns. The highest quality sidelock chucks will give runouts of around 8 microns and the highest quality collets will give runouts of around 11 microns, but some varieties of both types can add up to 30 microns to the total . A third option, and the one Guhring typically recommends, is the hydraulic chuck, which uses a reservoir of oil to equalize the clamping pressure around the tool.