AutoCAD Plant 3D 2013 Custom Blocks and Units

By Andy Davis

If you should need to add custom AutoCAD blocks to Plant 3D to represent pipe run components, then read on.  You need to pay particular attention to the units that you use when you define the blocks.

AutoCAD Plant 3D supports projects that use three different measurement units: Imperial, Metric and Mixed-Metric (metric lengths, imperial nominal diameter).

Pipe run components are assigned a nominal diameter when they are added to a piping catalog. The nominal diameters may be defined using either Imperial or Metric units.  

We already know that new pipe run components may be created from AutoCAD blocks.  However, these blocks may be used in two ways; they may inserted into a pipe run as ad-hoc custom parts or alternatively they may be added to a piping catalog, assigned to a piping spec and inserted into a model from the spec.

AutoCAD blocks may be defined in many different units, millimetres and inches are predominantly used by Plant 3D. In theory, the units used to define a block should not affect the size at which that block is drawn when inserted into a model as the blocks should be scaled to match the drawing units.

However, AutoCAD Plant 3D does not always scale blocks correctly.  Different combinations of block units, project units and units of nominal diameter produce differing results. 

After undertaking careful testing, tt would appear that the only way to guarantee correct scaling in all circumstances is to match the Block Units to the Project Units and Units of Nominal Diameter.

What this means in practise, is that you should create blocks for custom parts and actuators in the same units as your project and you should create block-based catalog components using the same units as the units of nominal diameter you specify in your catalog.