Three emails within one hour, all three with the same word in them: BOM. Purchasing wants to know what needs to be ordered for the new conveyor. The assembly foreman asks for a list per build group, because his crew erects the machine module by module. And the work planner wants to see per level which subassemblies have to be finished first. Three colleagues, one assembly, and yet they mean three different lists.
Inventor has an answer to that. The Inventor BOM views, structured, parts only and first-level, show the same assembly in three ways, each with a purpose of its own. Know the differences and you send every recipient the right list in one go. Mix them up and you cause adding-up work in Excel, double orders and debates about quantities. In this article we put the three views side by side, match them to the departments that ask for them, and look at how to get every list out the door without copy and paste work, among other things with a toolbox like Thundercad.
Three views, three different answers
The confusion starts with the word BOM itself, because in Inventor there is no such thing as one single bill of materials. The same assembly produces three lists that are all true, yet each answers a different question.
Structured: how it fits together
The structured view follows the tree of your assembly: main assembly, subassemblies and the parts beneath them. Viewed across all levels you see the complete build-up, with indented levels. This is the list that tells you how the machine goes together, and with that the natural list for anyone who builds or checks.
First-level: one floor at a time
Set the structured view to first-level and you only see what hangs directly below the level you are looking at: the build groups and loose parts of that one level. Whatever sits below those stays out of sight. That is exactly what you want when you plan, order or outsource per module: every subassembly becomes one line with a quantity, and the details belong to the list of that subassembly itself.
Parts only: everything counted flat
Parts only skips all the intermediate levels and adds up every part across the complete assembly. If the machine holds four build groups with six identical brackets each, parts only says: twenty-four brackets. The question this list answers is not how it fits together, but what is needed in total. For ordering and sawing that is worth gold; for assembling it is useless, because the build order is gone.
Which department gets which list
Once you know the three views, the only thing left to work out per request is which question the recipient is really asking. In practice it usually comes down to this:
| Recipient | Underlying question | View | Watch out for |
|---|---|---|---|
| Purchasing | What do I need to order in total? | Parts only | Bought items as one line, see the markings below |
| Assembly | In which order do I build? | Structured, all levels | State item numbers per level |
| Work preparation and planning | What must be ready per module? | Structured, first-level | A separate list per subassembly |
| Service and documentation | Which parts may ever need replacing? | Parts only | Filter for wear and spare parts |
Always state which view a list shows. A heading like "flat order list" or "build list per module" prevents someone from reading a parts only list as an assembly sequence, or the other way round.
The structure decides what each view can show
All three views look at the same source: the build-up of your assembly and the BOM structure each component carries in it. Four markings make the difference in practice:
- Purchased: a bought item with its own internal build-up, such as a gear motor with cover and plug, appears in parts only as a single line. Exactly what purchasing wants, because they order the whole thing, not its insides.
- Inseparable: a welded or pressed unit behaves as one part in parts only. The weldment counts as one item; its loose strips and tubes are ordered through the weldment's own list.
- Phantom: a helper structure that only exists for modeling, does not count itself and passes its contents on to the level above.
- Reference: counts nowhere. Meant for surroundings and reference geometry, not for anything that needs to be ordered.
A wrong marking is the classic source of "the quantities are off": purchasing getting the internal parts of a bought item on their list, or a bracket on reference silently dropping out of every count. A view can only show properly what the structure feeds it properly; how to design that build-up deliberately is covered in Your assembly structure is your BOM structure.
Sending every department its own list does not have to cost an afternoon. With Export BOM from Thundercad you turn the chosen view into an Excel file in your own template in a few clicks, with a different template per recipient.
Try 30 days freeExporting per recipient
On the drawing you choose per BOM table which view it shows, and that doubles as a useful check: the table on the overview sheet should be structured, the order list should not. For everything outside the drawing the same principle applies: decide the view first, export second.
That is also where the time gain sits. With Export BOM you export the bill of materials straight to Excel in your own template. Create one fixed template per list type with the columns the recipient needs: part number, description, quantity and purchase unit for the flat order list, the module structure for planning. How to set up such templates and why they replace the manual work in Excel is covered in BOMs from Inventor to Excel: always in your own template.
Give exports a fixed naming convention as well, for example project number plus list type. That way everyone can tell from the file name whether they are looking at a flat order list or a build-up list, even weeks later in an email attachment.
The four misses you want to prevent
- Structured to purchasing. Someone starts adding up quantities across levels by hand, and somewhere a multiplication goes wrong. Parts only does that adding up for you.
- Parts only to assembly. The quantities are right, but the build order is gone. The fitter lays out twenty-four brackets and gets to puzzle out where they belong.
- Item numbers mixed up. Item 7 in the structured list is a different part than item 7 in parts only. Whoever reads numbers over the phone without saying which list is organizing a misunderstanding. Use the part number as the key between lists.
- Markings forgotten. One bought item on Normal or one frame part on Reference, and the finest view counts wrong. Hence the check in the tip above.
Frequently asked questions
Why do the quantities in parts only differ from what I see in structured?
Parts only adds up across all levels and applies the BOM structure of every component while doing so. Bought items and weldments collapse into a single line, phantom structures pass their contents upward and reference parts do not count at all. If a quantity looks off, check those markings first and only then the model.
Can I use the same item numbers in every view?
No. Structured and parts only each carry their own numbering and they almost always diverge. So state on every list which view it shows, and use the part number as the fixed key whenever departments refer to the same article from different lists.
Do I have to build a fresh list for every department each time?
You do not. Record once per recipient which view and which columns they need, and work to that fixed recipe from then on. With Export BOM you pour the export into a fixed Excel template per list type, and during the free trial month you can simply try that with your own assemblies.