This is a quick assembly I’ve done not long ago.
It utilizes the path function, which is what I aimed at learning from this assembly. The mechanism itself has gear mates for the 3 sprockets, as well as a path mate for the chain itself.
Sketching and Modeling
Sprockets – these components are similar to gears but are somewhat different as their purpose is not identical.
In order to sketch the sprockets, a few simple steps had to be carried out. I created 5 different circles (figure 1), we have the inner circle where the key slot will be created later on. There are the addendum and dedendum lines, base circle and OD (outer diameter). most of these are for construction and reference, which has a lot to do with the mechanical design of gears (more on that in the future). the measurements are in figure 1.
Figure 2 shows us the involute line which originates from an arbitrary point chosen to be the center line. The arcs are defined and later on patterned about the center of the circles, which is also the origin point. This results in the shape of the teeth and the base circle.
After the sketch was completed an extrusion was done to receive a 3D model which looks like this:
A key way was added for practical reasons, a chamfer feature was applied to avoid stress concentrations.
Chain – Well, we all know what it does.
The creation of the chain consists of two parts, inner and outer parts. And they look like this:
First, it’s important to note that this is not how chains are made in real life. As you can see these two parts are not assemblable. in reality, there are 3 parts, inner, outer and the pins. These 3 parts constitute the chain on bikes and so on. but for simplicity’s sake, I took them out of the assembly and made them part of one of the components. in the assembly, I used these two parts in order to linear pattern along a path I’ve created.
Figure 5 – Path circles with measurements
These are the proportions I chose for the chain path, however, these are arbitrary and can be changed to suit whatever need.
After the first sketch, I added another sketch with 3 lines that are simply tangent to the circles, this wraps up the path sketch. The circles were later hidden to allow an easier representation of the assembly.
The first step is to import all of our components, we start with the path so that SolidWorks makes it fixed and fully defined as we insert it (the first component to be inserted into an assembly is fixed and aligned to the axes). Next, we add the 3 sprockets and mate them to be concentric with the 3 circles we drew in figure 6. Step 3 is to insert the 2 links of the chain (figure 7).
Then we linear pattern it in what is called “chain pattern” in SolidWorks, along the path to fill it and make the chain complete.
Which results in a beautiful assembly that looks like this:
and also like this:
Figure 9 – Assembly close up
Motion analysis and final thoughts
As with any assembly I produce, I like seeing how it acts, interacts and behaves while in motion (if the model is able to move at all). Since we have 3 identical sprockets, we know the gear ratio is 1:1
The quality is BAD, but, we can see that what we want moving moves nicely and according to plan.