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Causing a production line to come to an abrupt halt due to selecting the wrong tool for the job is every operator’s nightmare. Scrap, rework, broken tools and lost time are just some of the problems that can occur. While drilling operations and holemaking seem simple, they require tight tolerances and efficiency. There are three main categories of drills – and . Each has a place and knowing when to select which is necessary for high-production environments.

When you need the heavy hitters

Drilling large-diameter holes in a high-production environment requires a tool that can handle aggressive material removal while maintaining efficiency. That’s where indexable insert drills shine. These drills feature replaceable inserts, making them an economical choice for roughing out holes in materials like cast iron, steel, and stainless steel.

Indexable insert drills thrive in high-volume applications, particularly in industries like heavy equipment manufacturing, where productivity matters more than ultra-smooth finishes. They offer the flexibility of swapping inserts to optimize cutting performance in different materials—using positive rake inserts to reduce cutting forces in stainless and super alloys, or heavier-duty inserts to tackle interrupted cuts and high-feed applications.

However, indexable insert drills aren’t ideal for precision applications. If the goal is tight tolerances and smooth bore finishes, a different drill type may be a better fit. Additionally, these drills have limitations in depth capability, requiring alternative strategies for deep-hole drilling.

Indexable drills aren’t ideal for precision applications.

One example of an ideal use for indexable insert drills is a job shop machining flanges and heavy equipment components that needs to drill large-diameter holes in steel and cast iron. Since these holes don’t require a fine finish, an indexable insert drill allows for fast material removal, reducing cycle time before moving to a boring bar for final sizing.

Precision meets reusability

If your job requires a balance between precision and cost efficiency, provide an excellent middle ground. Unlike insert drills, these tools use carbide tips for accuracy while retaining a reusable steel body. Instead of replacing an entire drill, shops can swap out tips for different diameters or materials, reducing tool costs and inventory needs.

The flexibility of replaceable tip drills makes them ideal for shops frequently switching between materials like aluminum and steel and alloys like Inconel without requiring a full tool change. They provide better hole accuracy than insert drills while remaining more cost-effective than solid carbide. However, they do have their limitations—micro-diameter drilling and extreme speed applications typically require the rigidity of a solid carbide tool.

Replaceable tip drills makes them ideal for shops frequently switching between materials.

This type of tool is a great fit for a shop that produces products requiring frequent switches between different hole sizes and materials. Instead of stocking multiple dedicated drills, they can use replaceable tip drills, swapping out carbide tips to match each material while keeping the same tool body. This approach streamlines setup time and reduces tooling costs, making it ideal for shops handling varied production runs.

But when neither replaceable tip drills or indexable index drills fit the requirements of an application such as absolute precision, high speed and extreme materials, solid carbide drills come into play.

 

Precision powerhouses

When tight tolerances, high speeds and flawless surface finishes are required, solid carbide drills are the ultimate solution. Unlike their indexable counterparts, these drills are made from a single piece of carbide, delivering exceptional rigidity and cutting performance.

Solid carbide drills excel in challenging materials like titanium and Inconel, where advanced coatings like TiAlN enhance tool life and maintain superior surface finishes. Additionally, their extreme rigidity allows them to hold tight tolerances over extended production runs, something that may not be possible with replaceable tip drills, due to slight variances when replacing tips.

Solid carbide drills excel in challenging materials like titanium and Inconel.

However, solid carbide drills come at a higher cost. Since they lack replaceable inserts, if the tool chips or breaks, replacement costs can be significant. They are also not ideal for large-diameter roughing, where indexable drills are more effective.

One company that found success with solid carbide drills is a medical machining company that manufactures titanium bone plates that require small-diameter, high-accuracy holes with strict tolerances. Any variation in hole size could impact the final fit of an implant, so they rely on solid carbide drills with high-performance coatings to maintain tight tolerances and extend tool life across long production runs.

Improving performance and tool life with proper coolant

Drilling generates significant heat, and without proper coolant strategies, excessive temperatures can lead to premature tool wear, built-up edge (BUE), and poor surface finishes. Through-coolant drills provide a direct path for coolant to flush chips away, reduce heat buildup, and maintain tool longevity. But even with the right coolant flow, effective chip evacuation is essential to prevent chip packing, improve hole quality, and extend tool life. Understanding the can make the difference between smooth machining and costly tool failures.

For deep-hole drilling, through-coolant is one of the most effective ways to ensure chip evacuation and prevent tool failure. High-pressure coolant (1,000+ PSI) isn’t always necessary, but in tougher materials, it can be a game-changer.

When through-coolant isn’t available, peck cycles can be used as an alternative. By periodically retracting the drill, chips are cleared from the hole, reducing heat buildup. While this approach slightly increases cycle time, it extends tool life and improves hole quality, especially in deeper holes where chip evacuation is a challenge.

Beyond the drill: geometric considerations

Selecting the right drill type is only part of the equation — geometry plays a crucial role in hole quality and tool performance.

• The matter of margins: Double-margin drills provide straighter holes and better finishes but generate more heat, while single-margin drills work better in stainless steels and super alloys by reducing friction.
• Flute Count: Most drills have two flutes to balance strength and chip evacuation, but three-flute designs — common in solid carbide drills — allow for increased feed rates in materials like aluminum and cast iron.

Proper drill geometry can mean the difference between consistent, high-quality holes and premature tool wear or machining issues.

Matching strengths to needs

While cost is always a factor in tool selection, the key is choosing a drill that matches your machining needs. But the best choice isn’t necessarily the cheapest — it’s the tool that maximizes performance while minimizing downtime and scrap.

• Solid carbide drills: Highest cost but superior precision and longevity. Some can be resharpened to extend usability.
• Indexable insert drills: Best for high-volume roughing, with cost-effective insert changes.
• Replaceable tip drills: Provide a balance of cost efficiency and accuracy, reducing tooling waste while allowing for material versatility.

Common drilling issues

When machining, there are some common issues that operators can look out for when it comes to their drills.

• Chip welding (BUE): Use a proper coating (e.g., TiAlN), increase cutting speed and ensure adequate coolant flow.
• Poor hole finish: Reduce feed rate, increase spindle speed, and consider a double-margin drill.
• Tool Breakage: Check for excessive feed, tool runout and inadequate chip evacuation.
• Oversized holes: Use a solid carbide drill for better rigidity and verify tool holder and spindle condition.

Drill smarter, cut faster

Choosing the right drill isn’t always straightforward. Indexable insert drills are best for roughing large holes, replaceable tip drills offer flexibility and cost savings and solid carbide drills provide unmatched precision for high-tolerance work.

Justin and Andy from Kyocera offer advice on selecting the right Kyocera SGS drill tips for your applications.

All images provided by Kyocera Precision Tools.