If you’ve ever wondered why manufacturing uses a long list of spindle interfaces, the short answer is the continued improvement of the connection between toolholding and machine. Each interface includes its own unique advantages, and some target specific types of machining. Over time, these interface developments have produced incremental as well as revolutionary advances in repeatability and rigidity, the two attributes that all toolholding strives to provide to the fullest extent possible.
Look back two or three decades, and you’ll see that the R8 interface was very popular, followed by NMTB and ISO. All three featured manual tool changes on equipment that lacked today’s speed and accuracy. Modern machine tools require automatic tool changes to accommodate the sophistication of multi-process operations and to increase manufacturing speed with greater efficiency. To work with ATCs, manufacturers developed the BT, CAT and SK interfaces in Japan, the U.S. and Europe, respectively. Although each of these designs was different, all three featured a 7/24 taper.
When the HSK interface reached the market as a DIN standard, it represented the design contributions of at least 10 large companies that were part of the DIN group. Development focused on creating a better toolholding connection than steep-taper options, and succeeded in producing a much more rigid, faster tool-changing design with a uniform, standardized clamping mechanism and a shorter stroke that removes and inserts quickly. Unlike steep tapers, for which every machine designer created its own pull stud profile, the HSK spec includes a standard design that stipulates how to pull it into the machining center and hold on to the tooling. HSK offers much greater positioning repeatability than many other options because the toolholder returns accurately and predictably to the centerline of the machine. Where a steep taper holder falls somewhere in the 5 micron range for repeatability, an HSK toolholder runs in the 3 micron range.
Other interfaces enhance manufacturing from other perspectives on spindle interface designs or for other types of machine tools. At about the same time that HSK reached the market, BIG DAISHOWA introduced the BIG-PLUS system, which added face contact to the standard 7/24 toolholder, improving both repeatability and rigidity. Conversely, CAPTO sees its greatest use not in CNC machines but in lathes and mill turning. It was designed to replace straight-shank toolholders that didn’t offer enough rigidity in the machines. The CAPTO system offers as much repeatability as HSK, but its lobed design favors higher-torque applications and equipment.
Ten or 15 years ago, CAT holders were by far the most popular toolholding systems sold. In the last 5 years, we have seen many machining centers switch from steep-taper toolholding to HSK. These recent changes point to newer machines that manufacturers offer with HSK spindle interfaces. Even machine-tool manufacturers who focus principally on job shop customers now offer machines with HSK interfaces because they see that the industry wants to go in this direction for better performance.
As machine tools continue to grow in sophistication and spindle interface designs evolve to keep up, we’re likely to see evolutionary improvements on the toolholding standards in current use rather than a radically new design, at least for the foreseeable future. The introduction of smart technologies, both to machining itself and to the automation that powers an increasing focus on unattended production, may point the way to the next generation of interfaces. The smart toolholder already has begun to arrive, for example, in the form of the HSK-I design that has been proposed as an addition to the DIN standard. This concept includes more computer connectivity and can compensate to a greater degree for factors including rigidity, TIR and other problems in machining. Connectivity enables the toolholder to communicate its status to the machine tool, which can use that information to improve production.
The spindle interface designs of the past evolved to manage manufacturing on the machine tools of their day. As manufacturing’s precision, application range and overall expectations of productivity have continued to grow, spindle interfaces have evolved to keep pace. Regardless of which interface you choose for your applications, REGO-FIX has the toolholding solutions to keep any spindle happy – and every shop busy producing its best.
