MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
My threads are perfect, you may be over extruding. Or, bad cooling could cause the overhangs on the threads to droop. I would scale the cap a little on the second one so you don't have to do any post work.
The solid PLA blade I printed was pretty durable, but not the translucent. The kids broke that one pretty quickly.