I had thought of installing a pause command in the gcode so i could pop in a hex nut / bearing  or perhaps tubular insert to form shaft wall and then continue printing.

After my first print, using only Slic3r generated supports, I noticed that my overhangs left a lot to be desired, and were out of tolerance by quite a bit, stringy, etc. In terms of part design, it might be better to draw your own supports on problem overhangs. I had drawn my own supports into the part at only the most critical areas. I also asked Slic3r to generate its own support. The final part turned out really good. You can see it at this thread.http://www.soliforum.com/topic/2393/new … er-design/

Another thing I could add is to try experimenting with your own drawn supports for overhangs. Sure they will require a bit more work to cleanup, but they will also create a more accurate and clean overhang. I'll post an example later using the new stud mount extruder concept I have been working on.

Here is mine: Prefer chamfers over rounds in general. 

The "rounded" version on the right ends up a "hairy" mess at the bottom of the hole and pocket. This is because as you get to closing off each, your angles approaches 90 degrees.

The "faceted" version on the left is a nice and clean on the bottom.

(flat part you see is face down on the printer bed)

If you must use a round (such as to avoid stress concentration) try to make it vertical, not only so that it prints, but so the layers line up perpendicular to the "line" of high stress. That is, you want to be breaking the plastic strands, not separating two "glued" strands.

Here are some of my tips:

- Think about reducing overhangs from the very beginning of your design, and determine the face that's going to be printed first.

- Try to convert counterbore overhangs to 45degree chamfers instead, much easier to print a 45 degree overhang than a 90.

- Explore part trapping of features buried behind geometry. This is something that would be nearly impossible to mold, but easy to print, ie hex nut holes burried behind walls.

- 50% infill produces a surprisingly strong part.

Nothing earth shattering here, I know, but I'm also pretty new to designing parts meant only to be printed. I'm sure there are a lot of us that can learn from the rest of you! Thank you for your time.