Design Concept

Solid carbide drill bits are inherently brittle and expensive; in contrast, high-speed steel drill bits offer better toughness and lower cost, but their performance cannot be reliably maintained when the drill is excessively long. Indexable drill bits provide good value for money, yet they still require subsequent reaming or boring after drilling. Welded carbide drill bits, once worn, must be resoldered. Therefore, why not fabricate an integral carbide drill crown or cutting tip directly on a steel shank, thereby combining the advantages of a carbide cutting edge with those of a steel body? This is precisely the design concept behind indexable-crown drills.

This composite-structure drill not only combines the cutting accuracy and high cutting speeds of carbide drills with the cost-effectiveness of a steel shank, but also eliminates two time-consuming and expensive operations: drill replacement and regrinding of the cutting edge. While achieving the precision of brazed carbide drills, this type of drill enhances productivity and reduces manufacturing costs. The solid carbide insert crown features a self-centering geometric design, making it ideal for applications requiring tight dimensional accuracy and enabling users to meet stringent hole-diameter tolerances.

Key Advantages

(1) Quick Replacement

According to Mr. Choi Man-sik, Drilling Product Manager at South Korea’s YESTOOL, the primary advantages of indexable-insert drills are shortened production cycles and reduced manufacturing costs. Since their introduction 12 years ago, these drills have consistently competed with high-speed steel drills and brazed carbide drills, with their most notable benefit being the elimination of the need for regrinding and recoating. In fact, indexable-insert drills deliver such high productivity that they can rival solid carbide drills; yet, compared with solid carbide drills, their steel shanks offer a significantly lower cost.
Time savings are achieved by eliminating the need to remove the tool body from the collet when changing the insert; operators simply detach the cutting tip from the tool body and install a new one. If the operator needs to increase the hole diameter, only the insert needs to be replaced—there is no requirement to remove the entire tool body from the machine. A single tool body can accommodate inserts of multiple size specifications. Several methods are used to connect the insert to the tool body: YESTOOL employs two screws that pass through the insert to secure it to the tool body; Sandvik Coromant uses a screw on a pull rod that is threaded into the bottom of the insert, firmly and reliably clamping the insert onto the tool body; while ISCAR and Ingersoll Rand both utilize a keyway design to rotatably lock the insert onto the tool body.

Mr. Cui Wanzhi explained that replacing a toothed crown takes only 20 seconds and requires no post-replacement adjustments. Of course, the mating interface must be cleaned with compressed air to prevent damage to the cutter body.

Mike Gadzinski, Training Manager at ISCAR, estimates that replacing a carbide insert takes about 30 seconds, whereas changing an entire solid-tool assembly can take up to 10 minutes. He notes that the automotive industry has warmly embraced this technology, as minimizing downtime is of paramount importance to them.

(2) Cost savings

Manufacturers of indexable insert drills typically take pride in the tool’s low cost. Because only the insert is made of cemented carbide and is mounted on a steel shank, these drills are significantly cheaper than solid carbide drills. Although indexable insert drills are more expensive than high-speed steel drills, their cutting performance is far superior. Moreover, since a single shank can accommodate inserts of multiple sizes and specifications, only a small number of shanks need to be purchased.

Mr. Cui Wanzhi stated that while indexable-insert drills offer the lowest drilling costs, their metal removal rate cannot match that of the KRUZ-K series replaceable-crown drills, and post-drilling reaming or finish boring is almost always required. One of the key advantages of replaceable-crown drills, however, is that they eliminate the need for such secondary operations. When using solid carbide drills, although only one drill may be mounted on the machine tool at any given time, the warehouse must stock several: one awaiting regrinding, another just removed from the machine, and a fourth en route to the machining station—adding up to a substantial inventory. By contrast, with indexable-tip drills, all that’s needed is a small supply of tips in a drawer; when one wears out, it can simply be replaced with a new one.

According to Mr. Cui Wanzhi, a single cutter body can be re-equipped with new cutting inserts at least 15 to 20 times, depending on the specific application requirements. When proper clamping and cooling techniques are employed—YESTOOL recommends internal cooling—each insert can sustain machining for approximately 120 minutes when working with steel workpieces.

Different viewpoints

Dan Murphy, Regional Sales Manager at REM Sales, believes that indexable-crown drill bits are an excellent gap-filling cutting tool. He recommends using indexable drills for large-diameter holes and solid carbide drills for small-diameter holes. For hole diameters in between, if the operation is performed in high-volume batches, he would typically opt for regrindable solid carbide or brazed drills. However, when machining medium-sized holes, Dan Murphy feels that indexable-crown drills offer versatile performance without requiring a significant capital investment. Users need not worry about regrinding procedures; when higher performance than high-speed steel tools is needed but the volume of work is insufficient to justify the use of solid or brazed carbide drills, indexable-crown drills provide just the right solution. Dan Murphy is also open to employing indexable-crown drills on CNC Swiss-type lathes with tight hole-dimension tolerances, as these drills allow the cutting insert to be changed multiple times as required, thereby minimizing downtime.

However, Kirk Gordon of Gordon Engineering, a supplier of CNC drill-grinding machines, inspection systems, and customer equipment, offers a different perspective on indexable-insert drills. In his view, carbide drill tips demand very high rigidity during drilling, whereas steel shanks often lack sufficient stiffness—much like fitting a high-horsepower engine into a compact economy car. High-performance drill tips require robust shank support that ensures high strength and rigidity, as well as precise centering and reliable power transmission. Gordon is also skeptical about the advertised cost savings associated with indexable-insert drills. While he acknowledges that such tools could theoretically reduce machining costs, he believes that, compared with fully regrindable solid-carbide tools, the actual per-cutting-edge cost of indexable-insert drills may in fact be higher. He further argues that these drills are not as consistently effective as solid-carbide tools; for instance, even minor geometric deviations can significantly impact tool performance in certain applications. In addition, he points out that standard indexable-insert drills are generally unsuitable for drilling holes smaller than 1/4 inch (6.35 mm), thereby limiting their range of use.

Kirk Gordon believes that, overall, indexable-crown drills do not offer significant advantages compared with solid carbide drills. He outlines the costs associated with purchasing indexable-crown drills, replacing the worn tool body, replacing the crown rather than regrinding it, and the losses incurred due to reduced cutting speeds and diminished machining accuracy—specifically in terms of hole position tolerance, straightness, roundness, and dimensional accuracy. In his view, the optimal application for indexable-crown drills is for novice operators who may not yet be capable of replacing the entire tool but can readily change the crown. Even so, operators must keep the front end of the tool body clean and closely monitor it for signs of wear or damage.

Mr. Murphy of REM Sales disagrees with this conclusion. He argues that the root of the problem lies in people’s aversion to discarding tools and their reluctance to embrace new technologies. Purchasing more expensive cutting tools to alleviate concerns is a passive solution; an alternative approach is for operators to program a macro routine into the machine’s CNC system that uses indexable-insert drills, allowing the drill body to be discarded only after the inserts have been changed a suitable number of times. In his view, indexable-insert drills are best suited for machining holes with depths ranging from 3 to 5 times the diameter, whereas solid carbide drills are more appropriate for deep-hole drilling. Indexable-insert drills are by no means a “cure-all”; their primary applications are in machining softer materials, small- to medium-volume production runs, and relatively shallow holes, where they can deliver excellent performance. Moreover, when a batch of workpieces features holes of various sizes, using indexable-insert drills allows the drill body to cover an appropriate size range, so only the inserts need to be replaced. Solid carbide drills, on the other hand, are better suited for machining harder materials, deep holes, and high-volume, specialized production; while high-speed steel drills are ideal for single-use applications or for producing prototype parts.