Don't forget to mention, if you drop the blueprint on the ground and hover over the package it will show you the value of that item. That's what determines the blueprint quality that comes out of the tinkering bench. You will always get a good blueprint if you make sure the rating on the blueprints are all higher than the one you're trying to improve. I've found most of the time the first blueprint you put in is the one that gets improved but it seems like a 75% chance it'll be that one.