Gears and racks on CNC milling cutter without additional equipment and a modular cutter

    Probably many people looking at the DIY or Do It Yourself section were faced with the need to find / select the right pair of gears or a finished gearbox for your project. And also faced the difficulties of this search.

    The ability to manufacture gears on my own has long interested me. Factory methods of cutting gears with modular milling cutters, etc., by industrial methods, are of little use at home. And to make to order is crazy money for one piece or want a batch of 1000 pieces.

    Various attempts to cast epoxy and plastic gears ended in nothing.
    • For molding, you still need a sample, but this is not always possible.
    • Casting requires “file refinement”.
    • The resulting gears are fragile and often have defects.

    On gears made on a 3D printer, you can’t look without tears. Although some part of the tasks they cover.

    The idea that the right gear can be made on a 3-coordinate CNC machine without additional equipment did not immediately come to my mind. But, experiments have shown that the idea is working.
    Oddly enough, no one uses this method. They cut everything out with a modular cutter and on the thematic DIY forums there are a lot of questions “how can I make / order / find the gear”.

    After many experiments, I settled on the plugin option for inkscape .

    The plugin for inkscape “” (Copyright © 2011 Dave Web), slightly modified to form additional elements (center mark, hole, extra circle - pitch diameter, etc.)

    Rack plugin (Copyright © 2013 Brett Graham). Also refined on the little things.

    The 1mm module is the minimum module that a 1mm mill cuts without serious deviations from the required shape. Textolite or fiberglass is ideal as a material. Additional processing of finished gears and racks is not required.

    I use gears cut using this method in various projects. The gears withstand a decent load and wear until it is noticed.

    Characteristics of the tested rack and pinion drives

    Backlash rack and pinion

    The experiments showed that the play in the rack-pinion pair according to the micrometer with a time scale is 0.05-0.07 mm with a rail load in the range of 0.5-1Kg.

    This backlash was sufficient when the gap was set, so that the movement would be easy and without jamming. The gap is set with a rigid clamp of the rail with screws (oval hole on the rail). Gear on the axis of a stepper motor. The engine is tightly bolted to the base.
    Backlash in gear engagement is subjectively no worse than in a pair of factory metal gears with a 2mm module.

    Rail nonlinearity

    Unfortunately, I do not have the exact tool to measure the linearity of movement. Using a caliper, distance can only be determined that the linear movement error of 50 mm (in steps of a stepper motor) does not exceed 0.5 mm (it is difficult to determine more precisely).

    Some conclusions

    Using makeshift gears and racks for makeshift designs is a good idea.
    The cost of manufacturing is minimal for small batches and single copies.
    The main disadvantage of gear-rack drives: Noisier operation than using a belt or ball screw. However, this was to be expected.

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