Domain Adoption: Senior Mechanical and Automation Systems Engineer
Abstract:
This material details the design and implementation of a custom, cost-optimized 4th and 5th axis (tilt and rotation) add-on for a small-format 3-axis CNC machine (Fox Fräzer). The primary objective is to automate the precise machining of required cutouts into standard, off-the-shelf plastic crates intended for a modular production system (MPS). The solution emphasizes affordability, leveraging low cutting forces inherent to plastic milling to utilize 3D-printed components in critical load paths. Key innovations include a hybrid bearing assembly—combining inexpensive standard groove ball bearings for radial accuracy with 3D-printed gears for planarity and axial load resistance—and the selection of low-backlash planetary gears driving herringbone racks over costly industrial gearboxes (e.g., harmonic or cycloidal drives). Initial testing validates the stiffness and operational performance of this novel, 3D-printed kinematic chain.
Design and Implementation of an Affordable 5-Axis CNC Add-on for MPS Automation
0:04 Objective and Problem Statement: The project aims to build an affordable 4th and 5th axis add-on to automate the creation of precise cutouts (for cables, magazines, LEDs, etc.) in modular production system (MPS) crates, replacing time-consuming and imprecise manual methods (jigsaw).
0:41 Automation Requirement: Machining all five required sides of the crate conventionally would necessitate manual stops, rotation, and relocation after each side. The goal of the 5-axis fixture is to allow the entire process to be completed in a single setup by pressing "start."
0:52 Kinematic Solution: A fixture was designed with two additional axes (4th and 5th) to enable automated rotation and tilting of the work piece (the plastic box).
3:36 Cost Strategy via 3D Printing: Since only plastics are being machined, low cutting forces permit the incorporation of 3D-printed components in the load path, significantly reducing the overall cost compared to conventional industrial solutions (which can cost tens of thousands of Euros).
3:43 Drive System: The large 4th axis is powered by two geared stepper motors coupled to the rotation via curved herringbone racks. Planetary gears offering low backlash are used as a cost-effective substitute for high-end gearboxes like harmonic or cycloidal drives.
6:01 Hybrid Bearing Innovation: To reduce cost ($4 per unit) while handling the eccentric load and high play of standard groove ball bearings, a hybrid system was developed. Standard bearings provide radial accuracy, while 3D-printed orange gears provide planarity and resist axial/eccentric forces, resulting in an assembly cost of approximately €8.
7:21 Prototype Lubrication: A non-conventional lubrication technique utilizing regular lip balm is employed for the 3D-printed gears, selected for its ease of cleanup and suitability during rapid prototyping assembly and disassembly cycles.
10:32 Performance Validation: Initial testing successfully produced a finished box with multiple cutouts. The hybrid bearing/gear combination demonstrated surprisingly effective performance and sufficient stiffness for plastic machining.
11:08 Remaining Work: The system requires further electronics and software development, including the integration of vacuum extraction for chips and optimization of the control board wiring, which currently presents potential thermal density issues.
13:01 Open Source Availability: Design files for the 4th and 5th axis system have been uploaded, encouraging community feedback and collaborative development, particularly for an automatic clamping mechanism.