Pulley / Idler measuring jig

thingiverse

This jig measures concentricity in pulleys or idlers, and also checks for bent axles on stepper motors. It's designed around the dial indicator shown here: https://www.ebay.com/itm/STEINLE-Measuring-Meter-0-10-0-01-mm-with-Metal-Gauge-and-Tolerance-Marks-3105/172253576787 It's mounted on a 20x20 extrusion. You'll also need a looped GT2 belt, which I used with 200mm length, but you can use slightly shorter or longer ones. If using a 200mm belt, the extrusion needs to be at least 215mm long. The following fixings are required: 6 x M5x10mm head cap screws 6 x M5 Hammer Nuts 3 x M3 Hex Nut 3 x M3x20mm head cap screws To use the Nema17 mount, you'll need 2 x M3x10mm head cap screws. If you want to use a second dial indicator, your extrusion needs to be at least 315mm long and you'll need 2 additional M5x10mm head cap screws and 2 M5 hammer nuts. I usually mount two pulleys side by side, then the dial indicator, and turn the belt by hand for more control. This allows me to read exact values from the dial indicator before reading the deviation in both directions and adding them up. With this method, I've achieved a repeatability of about 0.02mm. Note that you won't get a deviation of 0 because the pattern of the teeth can be measured on the back side of the belt as well. However, since the pattern is very homogeneous, it's included in every measurement the same way and doesn't really matter. The files "Dial_Mount_left.stl" and "Dial_Mount_right.stl" are just for convenience to keep all screw heads on one side of the extrusion and avoid reaching across. If you use one dial indicator mount on each side, you can measure two pulleys by only fastening or unfastening two screws to move the dial indicator to the other side. This jig was designed specifically for the mentioned dial indicator with an 8mm mounting shaft diameter and a measuring shaft center that's 8mm above the ground when placed flat. This ensures the tip of the measuring point is at the same height as the pulley center. If needed, I can revisit my Fusion360 model to include parameters for different dial indicator dimensions. UPDATE: A slimmer version of the dial mount without a support underneath was added. It's symmetric and can be mounted on either side of the pulleys with all screw heads facing you. However, keep in mind that this one is more flexible without the support, which might introduce a bit more deviation. This doesn't matter if mounted vertically. UPDATE: A Fusion 360 archive file has been added with parameters to adjust according to your needs.