How to make circular workpiece path for feeding tracks

The most common mistake when designing such kind of machinery is choosing for path generation a section of the workpiece (usually in symmetry plane). Even if we provide enough tolerance around the generated section there is a major possibility making wrong designs. The reason is the workpiece’s length and geometry which affect the size of the feeding track.
There are two methods when designing circular feeding tracks. The first method is to build first the track, mate with the workpiece in an assembly and then copy geometry or remove material in order to make the circular track on the part. In this case a circular pattern of the workpiece in proper angle reveals the weak features of the part (possible interference). Disadvantages are the creation of difficult assemblies (many parts in a pattern) and a non-exact angle of pattern.
The second method is to create a blank part assembly with the workpiece (been positioned correct) and copy selected geometry from the workpiece to the part. After that we can create additional points and curves for circular path creation.
The second method offers a more general approach which cal be followed in many applications. First we must create a second coordinate system in the workpiece. Because it is more complicated to assembly parts only with datum planes we must create another coordinate system. When the part will be assembled with this coordinate system it will be fully constrained and in correct position and orientation (see figure bellow).

After the creation of the new coordinate system we can assembly our workpiece in the assembly. You notice that the workpiece is the first part in the assembly. This is because our reference geometry will be copied from the workpiece (see figure bellow).

We create the blank part (circular feeding track) and we place it in our assembly (through coordinate system).

We copy from the workpiece the external surfaces (the surfaces that will contact the circular track of the feeding track). From here we work only in our part (the circular feeding track) and use the assembly only for checking.

After copying the external surfaces we create additional points at the intersection of each three adjacent surfaces. Each intersection of three adjacent surfaces will produce a single point, which will be the theoretical corner of the workpiece (the most outer point). If the workpiece is symmetrical then only the two points in one side must be created (see figure below).

After making one point we make a circular pattern of it with the known rotation axis and angle of rotation. By connecting all the points of each pattern we produce a curve which is the path of the selected corner. For check we can create the point in the mirror side of the workpiece in order to see if it coincides with the curve. We follow the same procedure (creation of point, pattern and curve) for the upper corner of the workpiece.

Due to circular movement the workpiece has a one line contact in its inner surface (towards the axis of rotation) with the feeding track and two line contact in the outer one. So we have to create two more points in the inside area of the part which forms this contact line (both points belong in the symmetry plane).

Now we have four patterns of points, which will create four curves (paths of workpiece extreme points). Through these paths we can create a new section of the circular feeding track in a plane which passes through the symmetry plane of the workpiece. Checking this section we can see that coincides with the inner surface of the workpiece and is larger than the outer one. If the bottom surface of the workpiece forms a conical surface during its rotation, the corresponding side of the above section must has adequate clearance in order not to interfere with the workpiece (check clearance at assembly).

After making the appropriate section with rotation we can create a rotation feature which has the correct circular feeding track for transferring the workpiece in a different position.

Appropriate model analysis will reveal interferences and close tolerances between the two parts.