We are often asked questions about how openBOM calculates part quantities in Onshape documents. Although the answer is not really complicated, figuring out how to do so may cause some confusion. In this article, I’d like to expand a little on how openBoM calculates parts quantities.

However, before I get into that, let me first mention two ways to work in Onshape with parts to set some context.

(1) Assembly instances: using this option in Onshape, you can create Parts in Part Studios and instantiate them in an Onshape Assembly.

(2) Parts instances: using this option in Onshape, you can use Onshape Part Studio as an assembly and instance parts by transforming existing parts. Thus, you can assign the same name to identical parts you want to appear the same in the BOM. Note: at the moment, openBoM cannot designate an identical part number other by the same name.

So now, let me get into the “how”. In case you use Assembly instances (1), above, you create a BOM in openBoM without any special parameters or options. Part quantities will be calculated using the Part instance mechanism in Onshape.  Part quantities appear in the BOM per Part instance as you’d expect them to be.

In case you use Parts instances (2), above, use the “Group by name” option. Doing so will tell openBOm to create a BOM and calculate part quantities using an identical match to component names.

Note: Regarding Name edit in openBoM: unfortunately, you can not currently edit Name in openBoM. We’re working on an improvement, but for the moment, an ability to update Name in openBoM is limited. If you change Part Name, you can delete a previous part and insert a new one. A future Update will not be possible at this time.

Oleg, 22 May 2017