The MEMS MS Capstone at Duke University
Pulley Redesign Tutorial
This tutorial will cover how to design and print a pulley for a T5 belt for various shaft sizes. Although various outer diameters (OD) can be used, use one belt for all shafts for simplicity. Use a Nema 23 data sheet as a reference for the shaft dimensions [1].
Analyze the Nema 23, 17, and 14 shafts. BrecoFlex has information on T5 pulley specifications [4]. Find the pulley with the closest pilot bore to fit the project need.
Open the CAD software of your choice, such as SolidWorks. Create a circle sketch of a circle with a 24.60 mm diameter, as in Figure 1. The corresponds to the “Outside Diameter dK (mm)” on BrecoFlex’s website for a 16 tooth part with 25.46 mm pitch diameter [4].
Figure 1: First sketch in SolidWorks.
Extrude the sketch 18 mm.
Design pulleys with 16 teeth for the Moveo belts, so the tooth pattern below is appropriate. If designing a pulley with a different outer diameter, the 22.5-degree angle will decrease for larger OD and increase for smaller OD.
Sample calculation: a T5 belt has a pitch distance of 5 mm [5]. To ensure the arc length is 5 mm in a circle with pitch diameter 25.46 mm, the angle should be approximately 22.5 degrees. Use the Omni Arc Length Calculator to verify the calculation [3].
Click on the extruded face and create a new sketch, following the dimensions below in Figure 2.
Figure 2: Designing the first tooth.
Create a cut extrusion through the entirety of the cylinder. This will create the tooth for the belt to fit into. Read further about designing pulley teeth on BrecoFlex [6]. Ideally, the pulley gap should be minimized to reduce backlash.
Add a radius of 10 mm (vary this depending on the 3D printer available for the project). The single tooth cut will look like Figure 3.
Figure 3: First tooth cut.
Create an evenly spaced circular pattern from the extruded cut in the previous step. Remember that this design specifies 16 teeth, as in Figure 4. If unfamiliar with circular patterning, the SolidWorks documentation has resources to learn it [2].
Figure 4: Circularly patterned teeth in SolidWorks.
The final pulley should now look similar to this one in Figure 5.
Figure 5: Basic pulley design.
Extrude a 25 mm diameter, 1.5 mm thick, disk from both sides of the pulley. This will create the same pulley as in Figure 6.
Figure 6: Pulley with solid rims.
On the flat edge of the extrusion that was created, create a circular sketch and extrude cut through the entire design. The size of the hole should be 90% of whatever diameter set screw is needed. Remember that the 3D printer and the printing quality will affect small features like this. View Figures 7a and 7b as an example.
Figure 7a: Shaft bore sketch.
Figure 7b: Creating the shaft bore.
Create a sketch on the disk face and convert the inner pattern to a sketch. Extrude this pattern through the entire pulley, leaving as hole as in Figure 8.
Figure 8: Patterning the original shaft opening.
Next, increase the shaft opening slightly to make it easier for the shaft to slip in. Create a sketch on the extruded edge. Copy the pattern of the shaft opening and increase it by 0.25 mm. Now, extrude cut 10 mm. This will look like Figure 9.
Figure 9: Increasing shaft bore size.
Create a fillet on the outer edge of the shaft, as in Figure 10.
Figure 10: Adding a fillet to the pulley.
Create a chamfer on the inner edge of both cylindrical disks, as in Figure 11. This will help with printing.
Figure 11: Completed SolidWorks design!
Now, print this part. Refer to the 3D printing page for any help. It may be helpful to print a small cross-section of the piece to make sure it fits the belt and the motor shaft.
Tips:
- 100% infill
- Hotter than normal printing temperature (PLA 215)
- 0.16 mm layer height
- Slower than normal printing (25 mm/s)
References
[1] 23HP45-4204S Full Datasheet. StepperOnline. https://sites.duke.edu/memscapstone/files/2021/11/23HP45-4204S.pdf
[2] Circular Patterns Overview. Dassault Systemes SolidWorks Help. https://help.solidworks.com/2019/english/SolidWorks/sldworks/t_Circular_Patterns_Overview.htm
[3] Szyk, Bogna (2021). Arc Length Calculator. Omni Calculator. https://www.omnicalculator.com/math/arc-length
[4] T5 Pulleys. BrecoFlex Co. L. L. C. High Precision Drive Components. https://www.brecoflex.com/products/pulleys/stock-pulleys/t5-pulleys/#t5-pulleys-16mm
[5] Timing Belt – T5 Series (MISUMI). Misumi. https://us.misumi-ec.com/vona2/detail/110302654070/
[6] Tooth Gap Design. BrecoFlex Co. L. L. C. High Precision Drive Components. https://www.brecoflex.com/products/pulleys/design-guidelines/tooth-gap-design/
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