Schmid Maschinenbau was founded in 1972 in Biberach in Upper Swabia. The main products in the early days were hydraulic drilling units, but over the years the focus shifted to CNC machining centers. The company's customers come from the automotive industry, are manufacturers of fittings or suppliers of truck elements. In addition to the pure design and manufacture of the machine, Schmid now also provides complete solutions for various machining tasks, including clamping fixtures and automation. "A chain of factors influences the accuracy of the application," emphasizes Michael Bauer, Managing Director of Schmid. This also includes all mechanical components - from the connecting elements to the gears and couplings through to the bearings. "Individual elements and assemblies form the basis for meeting the high demands placed on the overall system."

Fast and functional tool changers
Fast and functional tool changers are central components of the machining centers from Schmid Maschinen. The mechanical device for automatically changing tools or measuring probes is installed in small Schmid machines as well as in large, custom-made machining centers for the production of wind turbines. The disk magazine has to act in a matter of seconds so as not to negatively affect the machining time of the machining center.

Schmid is particularly well known for its double-spindle machining centers, which enable efficient and flexible machining of medium and large series. The SE 410 machining center, for example, is designed for series production. Each of its two spindles can work on its own, providing the correction options in the X, Y and Z axes that are advantageous for series production. The two counter-rotating two-axis spindle modules face each other. There are four rotary tables on the swivel table in the middle, which increases the productivity of the machining center immensely. Each work spindle is assigned its own rotary tool magazine, and tools can be changed with the hollow shank taper within four seconds using the pick-up method. Thanks to the simple and robust design, the changing mechanisms are extremely resistant to faults.

The disk magazines are installed in tool changers and can hold up to 60 tools, depending on the version. © Schmid

Michael Bauer and his 60-strong team rely on four-point bearings from Rodriguez, which are installed in the tool changers of the SE 410 and also in the other machining centers of different sizes. "The changers have to run quickly and smoothly, and we have had the best experience with Rodriguez products in this respect," confirms the man from Biberach. "In addition to load capacity, reliability is a decisive factor for us," says Bauer. "A bearing must therefore be durable and low-maintenance."

Four-point bearing as a solution
Ball slewing rings have been part of the Rodriguez range for a long time. The four-point bearings are available in various rolling element configurations with internal or external toothing as well as without toothing. The raceways of the outer and inner ring consist of pointed arcs that cross at a single point in the center of the ring. The balls each have four different contact points on the rings. The purely axial load is only transmitted to two contact points; if the direction of the load changes, the contact points move to the opposite position. This type of bearing can therefore support axial loads in both directions, which would otherwise require two single-row angular contact ball bearings. Four-point contact bearings are primarily used where narrow axial guidance and small bearing widths are required.

The four-point bearings used by Schmid Maschinenbau are a custom-made product of type KDS. Tighter tolerances for axial and radial runout and the technical specifications provided by the customer require a customized internally toothed design with special toothing quality in these applications. For cases like this, Rodriguez has set up in-house production with a machine park. The customer-specific special solutions fall under the Value Added Products division, which is one of the company's core competencies.

Today, ball slewing rings with special modifications are required in many areas of application. The broad orientation of the Rodriguez machine park makes slewing bearings with external diameters of up to 1,400 millimetres possible - as well as slewing units with smaller diameters from 15 millimetres, which are increasingly in demand. Thanks to modern CNC lathes, shaft and ball screw spindles with an outer diameter of up to 100 millimetres can be manufactured in linear technology. as