Chris Atherton
In one of my previous posts, I wrote about the BOM functionality in Inventor and how you can alter the Bill of Materials structure within an assembly. Within the BOM utility you can alter the structure for each file to one of five preset values. Each of these values effects how an item appears on the BOM structured and parts only tabs thereby changing the parts list and line types on your drawing.
In this article I want to go a little further and talk about overriding this structure for individual occurrences of a component in an assembly. This can be of great help and is required if you need to reuse a file as a reference component. Let me give you a real life example:
Escalators ... Many moons ago I was an engineer who’s job involved designing and detailing heavy duty transit escalators such as the ones found on London Underground. Our design included a truss (the metal framework that is the structure/bones of the machine), tracks for the steps to role on and the brackets to hold them in place on the truss. We also had the balustrade (the metal “skin” of the machine that stops the public from seeing/falling into the machines moving components). Both these areas needed detailing; our track drawing needed to include the truss, tracks and brackets. The Balustrade drawing needed to include 2 trusses for 2 machines as well as the brackets and sheet aluminum that made up the “skin” that covered each escalator and the gap between the machines.
There were lots of options in Inventor to enable us to do this, but we decided that we were going to have two models and reuse the truss model twice as a sub assembly for the two different drawings. In the first drawing the truss needed to be detailed on the parts list & BOM and on the second drawing the truss was only used as a reference model that wouldn’t appear on the BOM.
The problem we have with this situation is that changing the BOM structure of the truss in the bill of materials for one drawing would also alter it in the second drawing. To get around this we needed to change the BOM structure of the occurrence of the truss in one of the assemblies not the default BOM structure of the file .... Let me try explain ....Each part and assembly file in Inventor has a default BOM structure which configures what BOM setting the file has (e.g. phantom, inseparable, reference, purchased, normal) when it’s added to an assembly. This default value can be set in the document settings of the file or is altered if you change the BOM structure of the file inside the bill of materials. Changing this value will affect everywhere this file is used, similar to editing a file and changing the colour or adding a fillet would affect all occurrences of that file in each assembly it’s used in.
We now come to the ability of inventor to override a BOM structure on each occurrence of a file. When you right click on parts or sub assembles in an assembly file you will find an option to alter the BOM structure. This menu only has two options however: Default and Reference. This option will allow you to specify for an individual occurrence of a file whether it uses the default BOM structure set in the document settings of that file, or whether that occurrence is set as reference only in the context of this assembly. If we imagine this as colours, you can change the colour of a part in a file however you can also locally override that colour at the assembly level thereby only effecting that occurrence of it; this occurrence BOM structure option on the right click menu works in the same way.
This is just a brief overview of this feature of inventor. There are lots of other situations it can be used in as well as other workflows to achieve what you need. For more info or clarification please contact us at Symetri.
