Linear and lead screw technology for CNC milling machine for prototype production

These small and compact CAD/CAM milling machines from Ingenieurbüro G. Kohlbecker are very easy to use and require no specialised knowledge of CAD or CAM technology. The purpose of the machines is to produce electrical and mechanical prototypes or devices quickly, precisely and simply, but with professional quality. The systems were sometimes developed for research and development laboratories, schools or users with a lean budget "" . Typical applications include the production of PCBs using the environmentally friendly insulation milling process, engraving, front panel milling, modelling and much more.
The technical requirements were primarily in terms of precision (in the 1/100 mm range), minimum backlash (<3/100 mm), mechanical load (<65 Newton) and speed (<150 mm/sec). In addition, the components had to be as maintenance-free as possible. A previous solution was sufficiently precise without load, but no longer under increasing load, and also had to be maintained and cleaned from time to time. The price of the previous applications was also too expensive. The machines therefore had to be redesigned and in particular maintenance-free, performance and production optimised and at the same time more cost-effective.

After a fairly long series of tests (approx. 2 years), an optimum, very flexible solution was found with a drylin® system from igus®, which could be precisely adapted to the technical requirements. A total of approx. 15 drylin® miniature guides are used as linear units and dryspin®-lead screw nut with pretension for the precise feed of the X- Y- and Z-axis. The carriage guides of the axis could be realised almost clearance-free, yet smooth-running, low-noise and maintenance-free. The dryspin®-lead screw nut fulfils the high requirements for the required backlash. The accuracy of the system is impressive with and without load, although it has been improved by a factor of 20 under load. The reason for the extreme improvement in resolution and accuracy is the change from a toothed belt drive to a spindle drive with a significantly higher transmission ratio. In the drive system, rigid motor couplings were placed on the clearance-free drive motors and the relatively short threaded rods were only guided through the lead screw nut, which is fixed on the linear axis, without any additional construction for a bearing. The required speed was achieved and exceeded. The design is also very "production-friendly", as it has become around 45% cheaper to manufacture the machines.