Where To Put Dimensions
The dimensions should be placed on the face that describes the feature most clearly.
Examples of appropriate and inappropriate placing of dimensions are shown here.
In order to get the feel of what dimensioning is all about, we might start with a simple rectangular block.
With this simple object, only three dimensions are needed to describe it completely. There is little choice on where to put the dimensions !
Engineering Drawing and Sketching
A Simple Guide to Dimensions
We have to make some choices when we dimension a block with a notch or cut-out (shown here on the right). It is usually best to dimension from a common line or surface. This can be called the datum line of surface. This eliminates the addition of measurement or machining inaccuracies that would come from "chain" or "series" dimensioning.
Notice how the dimensions originate on the datum surfaces. We chose one datum surface in the drawing – above right, and another in the one below.
As long as we are consistent, it makes no difference. (We are just showing the top view). In the drawing with the hole through the block ( one example at the top of the page and one shown below ) a dimension has been taken to the left-hand side of the object.
The Ø stands for diameter".