Here's is a little tutorial on the basics of creating holes and cylinders from existing mesh, most of which you should already know :) Basics: When all the polygons are nice and square, you can get away with creating basic holes or beveling them into cylinders etc. What if you what to move on to the next level of complexity. Visual Method: The visual method is easy, just select the four points as shown and roughly stretch them out until it looks like a decent circle, then just continue on as usual. It won't be perfect all the time but it'll do when precision is not required. Precision Method: This is an extension of the last method. Here we create an 8 sided disc, the same distance in the X and Z axes. This will be our template, we will be welding points from the base mesh to the points of the disc, doing away with guess work. This is fine if we are just creating one or two holes but what if you need to do a row of holes. Octagon Method: Well then, you come to the rig...