The ultimate aim of any machining operation is to ensure that components are manufactured to drawing; within tolerance; first time. Any other outcome simply adds cost, either in the form of rework or, worse still, scrap. While tool presetting is a proven contributor to right-first-time machining, many machine shops continue to ignore the tremendous advantages offered by this innovative offline process.
But just why is offline tool setting frequently pondered, but rarely tried? One reason might be that no one likes change: setting tools offline may necessitate re-evaluating job set-up and planning, and so many simply retain the age old method. This is a costly error of judgement.
Upon completing a job, a traditional machine shop will clear the swarf (possibly) and start reloading tools and the next program. Without an offline tool presetter, the operator has little choice but to rely on a more expensive, yet often less accurate presetter – the machine tool itself.
All programs need to know the location of cutting tools. If all toolholders and tools were perfectly identical, according to specification, the world would, indeed, be a happy place. In reality, of course, tooling has tolerances. Consider an indexable insert milling cutter; one insert tip may be a few microns higher or lower than its nominal position.
Sure enough, once the CNC program knows the offset values, it can compensate. However, 'teaching' the program these offsets requires 'touching off' each tool. Although this takes little more than a minute or two, with the trend of increased component complexity, most machining centres host 10s, if not scores of different cutting tools. It doesn't take a genius to determine that some set-ups are likely to run into hours. Even if a machine shop saves one hour per day, per machine, this can equate to 1,000 hours a year across five machines. In addition, while the machine is tied up 'touching off' tools to determine offsets, it cannot be cutting metal. Clearly, this method is wasteful and impacts directly on bottom line profitability.
Image: Zoller presetter in action
The answer lies with offline tool presetting, which, as the name suggests, presets tools and establishes the offsets before
tools are needed. What's more, the latest presetters can do this in a matter of seconds. As a result, when a machine requires a changeover, the tooling is ready to go. The upshot is that set-up times are normally reduced by such a substantial margin that payback of the presetting equipment is achieved quickly.
The vital element of offline tool presetting is the use of high quality equipment with an elevated level of precision and repeatability. Only this will ensure that first-off components are produced to specification. For instance, some basic manual presetters will only offer 10-20 micron accuracy, whereas the latest automatic presetters can measure down to a single micron. Furthermore, such equipment eliminates the touch and feel issues experienced commonly with manual presetters – human error is consigned to the history books.
Another disadvantage of manual presetters is that operators need to write down the measurement data and transfer it by hand to the CNC. Any errors here could lead to dangerous and costly machine crashes. Conversely, computer-based units are able to store the tool number and measurement data on the company's network. When the tool is required, the necessary information can be downloaded automatically.
Build quality is paramount when it comes to selecting a tool presetter. Always scrutinise elements such as the drives, scales, spindle and slide rails – have they been FEA designed and tested? Is telecentric optics technology deployed to eliminate 'wall effect' and fuzzy edges on spherical features? Are there specially integrated measurement programs for radius contour, chamfer width, wobble compensation and so on? Are different pull studs available?
Today, almost everything can be preset: milling cutters, drills, taps – even shrink-fit tooling. The same applies to back-ends: Capto, BT and HSK can all be accommodated. Using the latest presetters, tools can be quickly set-up and inspected for tool run-out, concentricity, height, wear and geometry, before being preset to nominal length and diameter position.
Ultimately, without accurate tool data, the machine that uses the tool becomes unreliable. Offline tool presetting is an assured way of helping machine shops reduce downtime, decrease tool inventory, lower scrap rates and increase part quality. All machining operations should begin with the offline presetting of tools.