Poor Man's 4th Axis cnc

thingiverse

I was determined to give my model cars a professional touch, so I decided to invest in a 4th axis for rotary engraving. The vague idea and intense software requirements made me hesitant at first, but it wasn't feasible to purchase a professional 4th axis set due to the hefty price tag. Luckily, I had a stepper motor leftover from my y-axis upgrade and a small chuck lying around, so I designed the *pm4a*. This DIY project was built on a desktop cnc-machine by Stepcraft using 6.5 mm birch plywood for the body and 5 mm Pertinax for the gears with a 1.2 mm spiral toothed flute. I used the following components: * 2 Ballbearings Type 6000ZZ (10 x 26 x 8 mm) * 1 Ballbearing Type 608ZZ (8 x 22 x 7 mm) * A small chuck (10 mm 3/8'' x 24 UNF) with SDS-Plus-adapter * NEMA17 stepper motor * A sharpened M8 machine screw and a selflocking nut (for the tailstock) * Some M3 machine screws The two gears have an unconventional cycloidal (round) teeth, which allowed me to create smaller teeth without corners. This was essential since my milling bit's diameter limited the size of regular teeth. To drive the motor, I plugged it into the X-axis stepper driver, ensuring the machine wouldn't move sideways but instead the workpiece would rotate. The distance traveled per revolution is calculated by dividing the workpiece's diameter by the gear reduction ratio (6:1). For example, my tires have a 40 mm diameter, so the circumference is 40 mm x π (3.1415) = 125.66 mm / 6 = 20.94 mm. I entered this value in the controller settings. When using the pm4a, it's a good idea to use some kind of cover to prevent dust from getting into the gearing. Visit https://www.zenziwerken.de/en/ for more innovative designs.