I'd suggest you should learn actual CAD software, like AutoCAD for example. Working in Illustrator on something that requires precision can be a complete pain, as the points and lines don't always join up perfectly. Add to that there's no in-built way to accurately draw lines coming off at a tangent, or perpendicular to a normal and you'll likely find it's a waste of time and money. CAD software will allow you to easily draw measurement lines, drill holes, etc, and quickly produce a drawing to an exact scale because that's exactly what it's intended for.