The traditional ‘Twist Drill’ has been around for more than 150 years and its overall design has changed very little during this time. This is recognition, if it was ever needed, of the invention from American mechanic Stephen Morse from Massachusetts back in 1863. 

While the style and general use of a standard twist drill remains very close to its original roots, there is a constant requirement to push the boundaries and find new ways to enhance performance, extend tool life and reduce overall costs. 

Tool Life Enhancing Technology

There are plenty of motivations to produce simple and reliable solutions to support and resolve manufacturing challenges in an efficient and cost effective manner. This has given rise to the development of a distinctive feature into the working end of the traditional drill.   

One example is the Continuously Thinned Web (CTW) technology developed by Dormer Pramet. Its rotary drilling range provides customers with a variety of benefits to support the life of the cutting tool, without compromising performance. 

Incidentally, the CTW geometry is a key feature of the R459 multi-material drill. Including the technology in the product range means it is easier to re-grind the drill and it offers a more consistent long-term performance. It will ensure the drill is restored to as close to its original properties as possible after regrinding, providing a cost effective solution in a simplified manner. 

CTW Explained

Traditionally, web thinning is performed as an additional operation after point grinding. A drill point is thinned by shortening the length of the chisel edge to reduce the thrust force needed when drilling. CTW technology simplifies the chisel thinning process as the depth is already set and therefore no adjustments are needed during regrind, regardless of drill length.   

CTW increases both flute volume and cross sectional strength. The combination of these elements ensures consistent forces throughout the drilling cycle, with little or no increase in power requirement as the drill penetrates deeper into the hole. This, in turn, allows increased cutting speeds and greater performance reliability without compromising tool life. 

A New Lease Of Life

Re-grinding a drill can be a cost-effective solution for an end-user to extend the life of a cutting tool, but it can be a complex procedure and needs to be performed accurately to ensure the product achieves a consistently good level of performance.   

Generally, a drill after the re-grinding process will retain around 75 to 80 percent of its original qualities and performance, but with CTW included, this increases to 90 to 95 percent. 

Also, a regrind company working with a batch of drills incorporated with the technology will reduce its lead time, compared with those that do not. This offers a quick turn-around for customers and simplifies logistics. Machine downtime is also kept to a minimum.

Installing the CTW technology into a drill not only enables the complexities of the re-grinding operation to be reduced but because an amount of the web thinning is built into the design, the symmetry of the tool is retained after re-grind. This means the drill will not degenerate over time and will maintain its torque strength after repeated re-grinds.

By integrating part of the web-thinning feature within the flute form, the design is effectively thinned throughout the life of the drill, without passing on the costs and difficulties associated with this additional operation to the user. Also, as thrust forces are kept consistently low, the result is less wear and tear on the machine tool, providing another time and cost saving benefit for the end-user.  

Test Results

CTW is currently featured in the R459 drill for applications up to 8xD in a wide range of materials. A key feature of the drill is its versatility in machining a variety of materials. Recent in-house testing conducted by Dormer Pramet using the drill on aluminium, hardened steel and stainless steel, showcased how the technology could withstand differing applications and conditions. 

During a test involving stainless steel 316L with cutting data of VC 35m/min at a feed of 0.1mm/rev (1,395 rpm at 140 mm/min), the drill ran for 30 minutes of contact time and showed a small amount of pick up, with a nice even wear scar across the cutting edges. 

Similarly when machining aluminium, the drill was run at Dormer catalogue data VC 285 m/min (11,340 rpm) at a feed of 0.26 mm/rev (2,950 mm/min). After 30 minutes of contact time, the drill showed minimal wear across cutting edges with a small amount of pick-up. 

In the development of the R459 with CTW, the cutting tool manufacturer performed a series of competitor testing, where the drill performed well against five others. To ensure fairness against the competition, all the drills were tested in the same conditions. With hole depth set at 40 mm and machining hardened steel (AMG 1.5), speed was 80 m/min at 5,092 rpm, with 0.09 mm/rev feed at 458 mm/min.

Among those tested, only one other competitor lasted the full 30 minutes, drilling more than 340 holes without any problems. In the same time frame, another lasted half an hour but offered a poor finish and noisy performance, while one more lasted the time but only at 7xD capability. The remaining two failed inside 20 minutes.

From the initial test, the best performing competitor was then selected to compare tool life using the same conditions. The R459 lasted for a further 80 minutes, drilling 900 holes without any problems, while the competitor was badly worn after completing the same operation.

The tests showcased that even with the CTW web-thinning feature included, deep-hole drills can perform successfully in a range of material applications. This consistent performance, enhanced tool life, improved regrind process and ultimately a reduction in costs, offers a win-win solution for all.