The tradition of ‘Twist Drill’ has been around for more than 150 years and its overall design has changed very little during this time. This is recognition of the innovative invention from American mechanic, Stephen Morse from Massachusetts back in 1863. However, there will always remain the ambition to improve on perfection!
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. Dormer Pramet’s philosophy has always been to provide customers with simple and reliable solutions to support and resolve their manufacturing challenges in an efficient and cost-effective manner. This set of ethos was a key element in their development of a distinctive feature into the working end of the traditional drill.
Offering long-term performance
Continuously Thinned Web (CTW) technology is unique to Dormer Pramet’s rotary drilling range and provides customers with a variety of benefits to support the life of the cutting tool, without compromising on performance. CTW geometry is a key feature of Dormer’s Force X range of solid carbide drills for applications up to 8xD. Including CTW in the range means that it is easier to re-grind the drills and offer a more consistent long-term performance. It will ensure the drills are restored as close to its original properties as possible, after regrinding, providing a cost-effective solution in a simplified manner.
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. Ricky Payling, Product Strategy Manager for rotary tools at Dormer Pramet, 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 on tool life.”
Advantages of CTW technology
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. Elaborating on this, Ricky shares, “Generally, a drill after re-grind will be at around 75-80 per cent of its original qualities and performance, but with CTW included, this increases significantly to 90-95 per cent.” He further highlights, “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 turn-around for customers, simplified logistics and machine downtime is kept to a minimum.”
Installing CTW 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 that 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.
Withstanding differing conditions
CTW is unique to Dormer Pramet and currently featured in its Force X range of solid carbide drills for multi-materials, including the 3xD R457 and R458, the 5xD R453 and R454, and the 8xD R459. A key feature of the R459 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 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 (1395 RPM @ 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 285 m/min (11340 RPM) 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 competitor testing, where the drill continued to perform 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 5092 rpm, with 0.09 mm/rev feed at 458 mm/min.
From those tested, Dormer’s R459 drill and 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 another lasted the time but only at 7xD capability. The remaining two failed inside 20 minutes.
Win-win solution for all
From the initial test, the best performing competitor was then selected to compare tool life using the same conditions. The R459 lasted for a total of 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. Even the most demanding customer will be pleased with these results and perhaps even Stephen Morse himself would be impressed to see how his invention has developed over the last 150 years.
Courtesy: Dormer Pramet