Making a Swiss watch requires micrometre-level of precision. Here’s how Paul Horn GmbH is helping Laubscher Präzision AG in its micro-machining work.
“That’s large by our standards,” says Marco Schneider, department head at Laubscher Präzision AG, as he measures the screw under a microscope. What he is examining actually has a thread size of S 0.6 (a type found in Swiss watches), a thread length of just 0.55 mm and a head diameter of 1.2 mm. This is the kind of component that Laubscher Präzision AG, based in the Swiss town of Täuffelen, is used to handling in its micro-machining work, where it uses tools supplied by Paul Horn GmbH.
Horn developed the µ-Finish tool system to cope with even the smallest of parts: with its outstanding cutting quality, changeovers that achieve precision down to the micrometre level, and low-vibration tool carriers, it is an exceptional piece of equipment.
There are several assemblies that go into the making of a Swiss watch, depending on the exact movement involved—the cogs, winding mechanism, drive mechanism, balance wheel, and motion work are some examples of these. Creating complex movements involves assembling numerous components in the tiniest of spaces, with screws holding everything together. A normal machinist would find producing these screws a hard nut to crack.
And despite their small dimensions, they still need to be synchronously transferred from the main spindle to a collet chuck in the counter spindle when it is time to machine the other side. Rather than callipers or an outside micrometer, it is a microscope with 50x magnification that is used to check the dimensions of these parts.
Laubscher Präzision relies on the Horn µ-Finish system to produce screws with a thread size of S 0.6 and a thread length of 0.55 mm. It manufactures some 30,000 screws solely of this type every year. Factoring in the many other types that also come off its production line, that adds up to several million screws that Laubscher supplies to the watchmaking industry annually.
Sharp Tools, Minimum Vibrations
The material used to produce the screws is free-cutting steel in the form of 3 mm diameter bar stock. The process sequence is as follows: facing of the screw head, longitudinal turning of the screw head diameter and of the diameter for the thread, thread cutting and parting off. The µ-Finish tools have a role to play at every stage.
“When you’re precision-machining miniature parts, it’s vital that the tools are extremely sharp and the tool holders produce hardly any vibrations,” explains Alain Kiener, Production Manager at Laubscher. The edge chipping and cutting performance that can be achieved are also essential to the micro-machining process, as any irregularity on the cutting edge will ultimately be reflected on the workpiece.
The Swiss company also specialises in producing micro components for medical technology—where the µ-Finish system once again comes into play, this time in the manufacture of venous plugs. Used for closing off vessels in electromedical applications, these components are pushed through a vein up to the heart via the groin in a minimally invasive surgical procedure. Their front section is then snapped off at the predetermined breaking point, closing off the vessel.
Boosting Tool Life to 1,000 Recesses
Every year, Laubscher is able to produce between 100,000 and 200,000 of these components, which are made of X5CrNi18-10 (1.4301). The predetermined breaking point has a diameter of 0.1 mm.
“At first, we ground the tool to create the predetermined breaking point profile ourselves. As the cutting quality of the Horn equipment is so good, however, we’ve managed to increase tool life to 1,000 recesses per insert,” says Schneider. When creating recesses up to a diameter of 0.1 mm in solid material, a sharp cutting edge and a vibration-damped tool holder are indispensable.
“Our tool system for micro-machining is also available with heavy metal tool holders, keeping vibrations to a minimum during machining,” says Horn application engineer Phillip Dahlhaus. “In medical technology, a very high surface quality is required. That’s because even tiny irregularities on the component, like grooves and burrs, can be a breeding ground for bacteria.”
The µ-Finish tool system is primarily aimed at micro-machining operators. Based on the S274 system, it features inserts that have been ground with outstanding precision. Every tool undergoes a comprehensive round of inspections during the production process to ensure that its cutting edges deliver these excellent standards of quality. Together with the central clamping screw and the precision-ground circumference of the indexable insert, the tool holder insert seat helps the system to achieve indexability to within microns. This in turn allows the insert to be indexed in the machine without the need to re-measure the centre height or any other dimensions.
In addition to its extensive range of standard profiles, Horn offers custom-made inserts with special designs. “Horn provides high-end tools for a wide range of applications, and solutions for everything from watchmaking screws and medical parts to hydraulic components. We use Horn tools on our Swiss-type lathe, our multi-spindle lathe, and almost everything in between,” says Kiener.
Horn itself is a German tool manufacturer and is represented in Switzerland by the company Dihawag. This partnership between Laubscher, Horn and Dihawag has been in existence for some 25 years, during which time Horn has successfully supplied tools for numerous machining solutions.
“It’s a fantastic partnership. Dihawag and Horn’s representatives are quick to respond to anything relating to our machining tasks, and we know that we can rely on them. We all work together extremely well and it’s amazing how quickly the tools are delivered,” says Kiener.
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