Here's a 4:1 gearbox for NEMA17 stepper motors that utilizes herringbone gears for smooth power transfer and minimal side-thrust from the gears. THIS DESIGN MAY NOT WORK FOR YOUR PRINTER WITHOUT ADJUSTMENTSParts have been designed to be 0.3mm larger. This should be taken taken into account when printing.If you are unable to assemble the parts as shown or if there is any backlash in the assembled gearbox, you will need to modify the design files/change part dimensions to fit your printer.For more details, assembly steps, design files, and a guide to designing printable gears in Autodesk Inventor see my post at https://0x7d.com/2014/08/41-gearbox-for-nema-17-stepper-motors/.