Belt pulleys- changing from 20 tooth to 36 tooth

  • axis pulley wheel diameter and teeth count.

    I'm using a h-bot with two of the wheels having teeth. Tronxy x5sa with dust 2 wifi.
    If I switch two of the pulleys wheels with teeth from 20 to bigger diameter 36 teeth do I need to make any configuration seeing changes to accommodate or will it just work?

  • i am assuming you want to change the pulleys on the stepper motor.
    Then yes you will need to adjust the steps per mm.

    but i would advise against that, as it will decrease resolution of your printer and can therefore lead to decreased print quality.

  • @chriskimbr As @Veti has said, you'll need to change the steps per mm. Assuming you use a 1.8 degree motor then a 20 tooth pulley will mean that 1 rotation (200 full steps) moves the belt 40 mm (20 teeth x 2mm pitch). So your steps per mm will be 200/40 = 5 full steps multiplied by your chosen microstepping of say 16X = 80 (micro) steps per mm. The 36 tooth pulley will move a belt 72mm for the same motor rotation so you will have 200/72 = 2.7778 full steps x 16 = 44.44 recurring micro steps per mm. You can see from that calculation that 0.1mm would be 4.44 microsteps but you can't have a fraction of a micro step so it would would get rounded down to 4 micro steps. Therefore positiona accuracy will suffer.

    Also, a 20 tooth pulley will have a diameter of around 12.7mm so a radius of around 6.4 mm. A 36 tooth pulley will have a diameter of around 23mm so a radius of around 11.5mm. Which means that the force that motor can exert on the belt will be about 55% of a 20mm pulley due to the lower leverage. This means that you will likely need to reduce your acceleration settings. Assuming you had accelerations set to the maximum that the motor would allow, then you would need to reduce them by about half.

    This is all assuming that it is the motor pulley that you want to change. But I'm a bit confused because you would also have to change all the idler pulleys in order to keep the belts parallel to the axes (edit -or as Mark says below, move the motor).

  • If you change the pulley diameter you will probably have to move the motor mount to keep the belt parallel to the guide rail.

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