123D Design tutorial for technical parts with accurate dimensions?
To try and give some concrete examples - I understand that you can create 3D shape primitives (rectangular prisms, cylinders etc) and assign them dimensions when you create them. I also understand that you can create 2D sketch objects and define their dimensions. What I don't find intuitive at all is how you can assign the dimensions of objects relative to each other. For example, say I want to make a 10x10x1mm bracket, with two 2mm diameter circular holes that have their positions on the face defined by the distance from their centers to the edge of the bracket. In a parametric CAD program, that is very easy to do in a 2D sketch and then extrude to a 3D solid. In 123D, I understand that I can create a rectangle primitive and then put holes in it using cylinder primitives - but it seems impossible to define the exact location of those cylinders relative to the edges of the rectangle; also impossible to create a sketch with two circles in it and a dimension defining the distance between their centers.
To give another concrete example: at the 4:20 mark in this video (from this Instructable), he draws a circle on top of an existing rectangular part, and then "centers" it by just dragging it around freehand and eyeballing it. Would it be possible to define the center of that circle relative to an edge, corner, or center of that existing rectangle? Or can 123D just not do that?
What I'd like to see, if anyone is up for it, is a step-by-step tutorial (preferably in video format) for making some sort of "technical" part where the dimensions matter and it isn't sufficient to just eyeball it and drag things around. e.g. a bracket like this (exact dimensions don't have to be what I drew here, but you get the idea). All of the tutorials I've seen so far - including the official Autodesk ones - seem to just focus on eyeballing it/free-handing dragging parts around.