The traditional ‘Twist Drill’ has been around for more than 150 years and its overall design has changed little during this time.

This is recognition, if it was ever needed, of the innovative invention from American mechanic Stephen Morse from Massachusetts back in 1863. However, while the style and general use of a standard twist drill remains 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.

Dormer Pramet’s philosophy has always been to provide customers with simple, reliable solutions to support to their manufacturing challenges in an efficient, cost-effective manner. This was a key element in its development of a distinctive feature into the working end of the traditional drill.

Continuously Thinned Web (CTW) technology is unique to Dormer Pramet’s rotary drilling range and provides a variety of benefits to support cutting tool life without compromising performance. CTW geometry is a key feature of the newly released R459 multi-material drill for applications up to 8xD, produced under the company’s Dormer brand. Including CTW in the range means it is easier to regrind the drill, ensuring the drill is restored to as close to its original properties as possible after regrinding.

Traditionally, web thinning is performed as an additional operation after point grinding. A drill point is thinned by shortening 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 no adjustments are needed during regrind, regardless of drill length.

Ricky Payling, Dormer Pramet’s application specialist for rotary tools, explains: “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.”

Regrinding a drill can be a cost-effective solution to extend the life of a cutting tool, but it can be a complex procedure and must be performed accurately to ensure a consistently good performance.

“Generally, a drill after regrind will be at around 75%-80% of its original qualities and performance, but with CTW included, this increases significantly to 90%-95%,” adds Payling. “Also, for a regrind company, working with a batch of drills with CTW included will significantly reduce its lead time, compared with those that do not. This offers a quick turnaround for customers, simplified logistics and machine downtime is kept to a minimum.”

Installing CTW into a drill not only reduces the complexities of regrinding, but because an amount of the web thinning is built into the design, the symmetry of the tool is retained after regrind. This means the drill will not degenerate over time and will maintain its torque strength after repeated regrinds. By integrating part of the web-thinning feature within the flute form, the design is effectively thinned throughout the drill’s life, without passing on the costs and difficulties associated with this additional operation to the user. Also, as thrust forces are kept consistently low, there is less wear and tear on the machine tool, providing more time and cost savings for the end-user.

Unique to Dormer Pramet, CTW currently features in its new R459 drill, though the company hopes to expand its use to other drilling ranges in the near future. A key feature of the R459 is its versatility in machining various materials. Recent in-house testing by Dormer Pramet on aluminium, hardened steel and stainless steel, showed how CTW could withstand differing applications and conditions.

During a test in stainless steel 316L with cutting data of Vc 35m/min at a feed of 0.1mm/rev (1395rpm @ 140mm/min). The R459 ran for 30 minutes 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 285m/min (11,340rpm) at a feed of 0.26 mm/rev (2950 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, Dormer Pramet performed a range of tests where the drill performed well against five competitors. To ensure fairness, all the drills were tested in the same conditions. From those tested Dormer’s drill and one competitor lasted the full 30 minutes, drilling more than 340 holes without any problems. Another lasted half an hour but offered a poor finish and noisy performance, while another 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 tested to compare tool life. The R459 lasted a further 80 minutes, drilling 900 holes, without any problems, while the competitor was badly worn after completing the same operation.

The tests showed 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 offer a win-win solution for all. Even the most demanding customer should be pleased with the results – just maybe, even Stephen Morse would be impressed to see how his invention has developed during the last 150 years.

www.dormerpramet.com