As a follow-up to my last post, here are a few different 3D printed rotary attachments that where made by Crossgates Crafts. These are all designed for use with a diode laser system, but they are well engineered and have good examples of how to minimize costs without sacrificing quality.

The simplest solution does not even have a stepper motor, instead it relies on the motion of the X axis.  By tying the rotary axis to the edge of the Y axis and using a rubber band to act as a belt, movement along the X axis makes the whole thing roll.  This only uses two bearings, some threaded rod and a few pieces of random hardware.  

The down side is you can only mount the material on one side, or in this case via a center hole.

Next we have a roller setup, you can see how the use of different wheels can allow you to support very odd shaped parts.  This requires a stepper motor, 6-7 bearings, a belt and gear set and various supporting hardware.

One of the downsides here is that the whole setup is very tall. In this case it is designed for an open framed laser rig that can have feet added to it to raise it up to any height, but for our setup this would be much too tall.  You could make this shorter, but it will always eat up some vertical height.

Finally we have a chuck style setup.  This has the unique idea of using simple rubber bands and 3D printed pulleys rather than a proper toothed belt and pulley set.  This saves money and simplifies the setup.  it is using a stepper motor, 4 bearings, some form of base that allows the tail stock to slide back and forth and various supporting hardware.

Notice that this setup allows for different size pullies to be substituted in.  The idea being that you pick a pully that closely matches the diameter of the part you are cutting, that way the rotary setup acts like a roller setup.

This also highlights the advantage of the chuck style setup. By changing out the spindle and quill (pointy part of the tail stock) you can mount almost any part to the setup.