Schaller, based in Nuremberg, Germany, is a globally renowned manufacturer of guitar parts, including machine heads, bridges, tremolos and strap locks. Helmut Schaller founded the company at the end of 1945 as a repair workshop for radios and other electronic devices. In the early 1950s, he began to develop amplifiers and speakers for musical instruments. Through a business partnership with an instrument maker, Schaller began developing and manufacturing guitar parts, and by the 1960s, the company had become one of the most prominent guitar part suppliers in Europe. Since then, leading guitar manufacturers such as Gibson, Fender and Ovation have relied on these parts.
The internally cooled jet whirling system, which was launched at AMB in 2018.
The production team, led by Dominik Weininger, plant manager at Schaller, uses modern machinery and equipment to turn and mill the precise components required to produce excellent sound quality. One such piece of equipment is an internally cooled jet whirling system from Germany-based Paul Horn (Horn), an investment that has enabled the team to halve machining time for the worm thread of the machine head screw as well as significantly improve the surface quality of the component.
Schaller machine heads.
Precise worm gears
The machine heads on plucked instruments are used to tighten and tune the individual strings. They are at the top of a guitar and have a transmission to ensure a high degree of precision when tuning the strings. Other important properties are ease of movement and stability due to the self-locking mechanism. The higher the precision of the components, the higher the quality. The transmission of the machine head uses worm gears, as these are the only gears to enable precise adjustment and reliable self-locking.
A central part of the machine head is the adjusting screw with the worm thread. Nicole Gawatsch, head of the CNC turning and milling department at Schaller, saw potential for improvement in this thread. “We previously milled the worm thread with a side milling cutter,” she said. “The machining time required was too long for us and we often had to take the part and re-clamp it by hand.”
Weininger added, “We became aware of Horn’s internally cooled jet whirling system at AMB 2018 and immediately contacted our Horn sales representative.”
Initial discussions with Horn about the jet whirling system and the start of the project quickly followed.
Whirling system with internal cooling
The whirling method has been around since 1942 and had not seen any major developments for a long time. Conventional thread whirling is a method that is primarily used on Swiss-type lathes to produce bone screws, or on a large scale, to produce threaded spindles. To implement the process, a rapidly rotating whirling head is positioned in front of the guide bush of the Swiss-type lathe, eccentrically to the workpiece axis. The rotating workpiece is fed axially into the whirling head, which is pivoted to achieve the specified lead angle of the thread.
Horn launched the jet whirling system with internal coolant supply at AMB in 2018. This system affords optimised cooling directly at the cutting edge and was developed by Horn in conjunction with Germany-based W&F Werkzeugtechnik (W&F).
The major challenge was to bring the coolant directly to the cutting edge in a confined space and to do this at high whirling speeds. The cooling channels partially integrated in the insert seat direct coolant to each cutting edge. In addition, the coolant flows through the chip space. By cooling the cutting edges directly, this system enables long tool life to be achieved. What is more, when used in conjunction with the stable whirling unit, it achieves better surface quality on the workpiece.
Thanks to the patented W&F interface with its face-and-taper contact system, the whirling head boasts high changeover accuracy and is easy to exchange with just three screws. The internal coolant supply reduces the risk of chip build-up between the cutting inserts, which offer radial and axial run-out of 0.003 mm. The maximum speed is 8,000 rpm.
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The internally cooled jet whirling system in use at Schaller. It has allowed the company’s production team to halve machining time for the worm thread of the machine head screw, improve surface quality of the component and increase tool life.
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The internally cooled jet whirling system in use at Schaller. It has allowed the company’s production team to halve machining time for the worm thread of the machine head screw, improve surface quality of the component and increase tool life.
The first tests at Schaller were not an instant success. “The problem was that the coolant pressure of the machine was too low,” explained Peter Rümpelein, sales representative at Horn. “The whirling unit requires a high coolant pressure for satisfactory operation, but the machine only delivered a low pressure.”
After producing 20,000 components, the bearings of the whirling unit had to be replaced due to insufficient cooling. Gawatsch then moved the whirling process to a Swiss GT sliding-head lathe from Switzerland-based Tornos. The large pump capacity of the lathe ensures that the high coolant pressure is delivered. “The high pressure provides cooling and lubrication for the unit,” observed Rümpelein.
Machining time halved
After a delayed start, the whirling process now runs reliably. “The whirling unit has been running 24/7 in the machine for over a year,” stated Weininger. “We are very satisfied with the tool system.”
The successful change in the process is also reflected in the processing time. Previously, Gawatsch needed about a minute to mill the worm thread. Conventional whirling takes 40 seconds. “With internally cooled whirling, we have halved the machining time to just 20 seconds per component,” Gawatsch said. “Given the incredibly high number of components we process each year, this is an enormous saving.”
In addition to the reduced machining time, the surface quality of the finished components is significantly improved. Moreover, the service life of the indexable inserts has increased many times over.
Only one version of the whirling head with insert seats for the type S302 indexable insert is used at Schaller. “We only need to change the inserts for the different threads,” continued Gawatsch. For whirling, the S302 system, which has three cutting edges, is mainly used at Horn. There is a high degree of manufacturing precision when it comes to grinding the cutting inserts.
The three cutting edges are subject to a length tolerance of less than0.005 mm when turned. This ensures the excellent concentricity of the entire system, the high changeover accuracy when indexing the inserts and the outstanding surface quality. “The cutting edge profile of the S302 system can be adapted to almost any special requests from the user, whether it’s for single or multi-threads,” concluded Rümpelein.
Schallerhttps://schaller.info/en
Paul Hornwww.horn-group.com
W&F Werkzeugtechnikwww.wf-werkzeugtechnik.de/en
Tornos www.tornos.com/en