Parametric Timing Pulley v4

by JamesNewton, published

Parametric Timing Pulley v4 by JamesNewton Dec 3, 2012


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This OpenSCAD script makes many different types of pulleys for just about any sort of timing belt. This latest version adds support for shafts that have a flat, for multiple nut sizes based on the shaft diameter, adjustable flanges, and for making pulley sets, where the second one is based on a ratio of teeth from the first one. The prior version added support for any number of setscrews and allowed them to be at an angle. The original (By Erik de Bruijn) supported threaded shafts with a recess for a nut to hold the pulley in place, or an even number of set screws printed in a hub with a (capped) teardrop hole. The original works well with the Synchroflex(R) timing belt,1500Lx10Wmm from RS (order code 474-5892), spliced in half (to 5 mm width).


Render with F6, as F5 doesn't always work correctly with this script. If rendering is very slow, change $fs to 1 and $fa to 12; at least while working. Change the parameters for your belt, and for your pulleys. The samples supplied include a small pulley for a stepper motor with a flat on it's shaft, a large pulley with a 4:1 ratio of teeth to the first one and a large hub with 3 setscrews at a slight angle, and another small one with a nut recess for a threaded rod.


toothType // 1 = slightly rounded, 2 = oval sharp, 3 = square. For square, set the toothWidth a little low.

$fs=0.2; // defaults 1, 0.2 is high res
$fa=3; //defaults 12, 3 is very nice
//NOTE: If rendering is very slow, change $fs to 1 and $fa to 12; at least while working.


pitch // distance between the teeth
beltWidth // the width/height of the belt. The (vertical) size of the pulley is adapted to this.
beltThickness // thickness of the part excluding the notch depth!
notchDepth // make slightly bigger than actual, to avoid outward curvature in the inner solid part of the pulley
toothWidth // Teeth of the PULLEY, that is.
numTeeth // this value together with the pitch determines the pulley diameter
flanges // the rims that keep the belt from going anywhere, 0, 1 (on the top) or 2
flangeHeight // how much the flanges angle in toward the inner diameter of the pulley.
shaftDiameter // the shaft at the center, will be subtracted from the pulley. Better be too small than too wide.
// If there is no flat, and no setscrew, we assume the shaft is threaded and a recess for a nut is added.
// The nut size is selected automatically based on the shaft size, and reported in the compile log.
shaftFlatDiameter // the diameter of the shaft when measured at a flat milled in the shaft. 0 if the shaft is round.
hubDiameter // if the hub or timing pulley is big enough to fit a nut, this will be embedded.
hubHeight // the hub is connected to the pulley to allow a set screw to go through or as a collar for a nut.
hubSetScrewDiameter// use either a set screw or nut on a shaft. Set to 0 to not use a set screw.
hubSetScrewAngle // change from 90 to angle the setscrews
hubSetScrews // 1 is usually fine, 3 allows centering

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http://www.sdp-si.comhttp://www.sdp-si.com not only has a great calculator, but they also sell belts! Prices are fantastic, and they provide the full specs for the belt, unlike McMaster-Carr. Sadly, they seem to be discontinuing some of the belt lines. Hope the one you need is still available.

SDP/SI has an absolutely mac-daddy timing belt / pulley center distance / ratio calculator.


Please let me know if you run into any problems by posting the parameters you used here so I can try to duplicate and correct the issue. 

Any other features you want to see? I have one vote for an option to support a lego motor shaft. 

Maybe the next version will add support for a captured nut for the set screws? The one wheel has it:


Highly Configurable Wheel (One Wheel To Rule Them All)