High-performance Drill Bits

Increasing productivity depends on boosting drilling speed, the penetration rate or both. The definition of high-speed drilling is somewhat arbitrary. Some drill manufacturers refer to “high-speed drilling” as drilling at spindle speeds fast enough for penetration rates three to ten times greater than those considered conventional. Others simply define high speed as drilling faster than usual.

Factors that affect drill bits at lower speeds become more pronounced and critical when drill bits are used at a higher speed or feedrates. The build up of heat, chip removal as the tool feeds deeper into the hole and runout all have to be considered when drill bits are running at high speeds.

As drilling feeds and speeds increase, the challenge of providing sufficient coolant to remove the chips becomes more critical. The volume of chips produced, if not removed, can cause chip jams, recutting and high heat that shorten the life of many drill bits. When reducing cycle times by 90 percent, there is simply not much time to remove chips, and a high pressure coolant flow is required. Many older machines can not supply sufficient volumes of coolant to remove chips but, in some cases, those machines can be retrofitted to increase coolant flow.

At lower speeds, high-speed steel (HSS) drill bits are often effective, and provide a tool with relatively high bending strength and toughness. However, at higher speeds it is necessary to use carbide drill bits or ceramic tools. These tool materials trade some of the toughness of HSS for greater wear and heat resistance.

Drill and toolholder balance also becomes critical for drill bits operating at speeds that exceed 10,000 rpm. Shrink-to-fit and hydraulic toolholders usually are the relied on to stay within acceptable limits for out-of-balance at those speeds.

Older machine tools often have can not provide the concentricity necessary to take full advantage of today's new, precision drilling systems, which feature more advanced drill bits. Total runout should be held to 0.001 in. While lathe drilling, with both the turret and chuck contributing to hole concentricity, runout at the tool should be no greater than 0.0005 in.

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