Here is a start to finish (mostly) of a project from idea, to CAD, to print for mounting a dial indicator on to the extruder to help with leveling.
The CAD program is Alibre, which has a personal edition for about $200. The learning curve isn’t too steep, and while Sketchup is easy and free, parametric solid modeling is ideal for a part like this one.
The dial indicator was $38 from Amazon – http://www.amazon.com/gp/product/B006YD7G36/ref=oh_details_o02_s00_i00
And the magnets are these- http://www.amazon.com/Neodymium-Magnets-inch-Cylinder-N48/dp/B001KV9RAW
This didn’t end up being the final design. I will cover that in Part 2.