Why are instanced sketches not included in the assembly's BOM?

StephenG

(Note: This question is related to a prior question I submitted: "WHY ARE NON-PART BOM ITEMS LIMITED TO PROFESSIONAL AND ENTERPRISE USERS?")

I do not understand the rationale for not including instances of sketches in an assembly's BOM. What is the harm? Could someone explain?

I am trying to simply workaround a current limitation in OS of not having access to BOM Item functionality as a Free user. 

StephenG

@matthew_stacy, @konstantin_shiriazdanov

My rationale for wanting to add non-geometrical items to my assy BOM was to record the need for dispensable consumables critical to the assemblies function. I was modeling an outdoor wood product and during the design I wanted to record the use of a specific wood preservative and glue/adhesive. I know there are other ways to specify these things, but I didn't want to create a drawing and start propagating it with notes, or use OS comments which are easily overlooked. The assy BOM seemed like the logical choice to record this info. 
 
Due to the lack of access to BOM Item functionality, creating a "dummy part" was the approach I used. When I began, I asked myself what is the simplest thing (geometry wise) that would minimize visualization clutter and not mess with assy mass properties: a single point in a sketch was the obvious choice.  Turns out that a sketch was not a wise choice because you cannot assign metadata properties to it. So for this reason it doesn't make sense for instanced sketches to be included in the BOM. 

Ok, lets move up food chain, how about a curve created from a sketch line. Metadata properties can be added to curves, but wait you cannot insert/instance a curve into an assembly. Well, moving up the geometry food chain how about a simple planer 3-sided surface. This works, however, the mass property surface area calculation is wrong.

I ended up creating a OS Document full of small surfaces representing classes of non-geometrical BOM items. I instance the surface and then manually enter required info into the BOM entry fields. This is a imperfect workaround to address the lack of access to BOM Item functionality. 

It would be nice if Composite part could reference sketches, curves, and surfaces, or be created "null", but at least 1 part and only part data is supported.

Time to move on to developing the next work around.  

tim_hess427

It seems extremely rare that someone would want to add a sketch to a BOM outside of a situation like yours where you're trying to use it as a workaround.

Onshape would be creating more work for most people (having to remove sketches from BOMs) than helping the edge cases like yours where it's wanted.

It seems like what may be more helpful is a way to override the default BOM to add/edit things. Then you could add your items. But, at that point, I guess you could just make the BOM manually, anyway.

StephenG

@tim_hess427
Thanks for the comment.

Your comment gave me an idea: attach a "table" with the same number of columns to the bottom of the OS BOM and manually enter non-geometric BOM items. Unfortunately you cannot attach a table to the bottom of the BOM table; only eyeball position it. Furthermore, it is not possible to associate the column separator lines of a table to the BOM table columns. Therefore, this hybrid BOM table approach is not practical.

Granted, this specific use case is a workaround for the lack of access to BOM Item functionality, but this limitation affects (hampers) a workflow where a design (geometric representation) evolves from nothing, to a very simple (2D cartoon), to a simple 3D something, to a refined 3D model.     

It is unfortunate (shortsighted) that OS insists that a BOM item must contain at least 1 bounded surface, unless you are a Professional/Enterprise user with access to BOM Item functionality. From a design workflow standpoint I like the capability to define a part without the need to create any, or using highly simplified geometry (a point, coordinate system (mate connector), or 2D sketch). Essentially, a placeholder for something that is to be modeled, but what  the part design looks like is a mystery.

In OS you can create null assemblies and pre-create/evolve the entire assembly product structure ahead of time. It would be helpful if the same capability existed to create null parts devoid of geometry, or be comprised of simple sketches. I understand that OS multipart Part Studios complicates things, but it should be a simple thing to inherit/transfer properties (metadata) from a dummy part to the real part, or replace instances of a null part, or sketch, or surface in an assembly with the real part.

It appears OpenBOM would be a better solution, but you need to have an OpenBOM Professional/Enterprise paid subscription to get OS BOM integration. That makes it a No-Go for me. I did take a peak at the "14-Day Trial" and it appears that OpenBOM is really intended to completely replace OS BOM functionality where the BOM info no longer appears in classic 2D engineering drawings documents. Essentially, the product BOM is completely managed/accessed though a different external DB application. OpenBOM integration appears to be one-way in that one can upload/update OS BOM info into a more complete/comprehensive BOM that supports a broader range of usage within an enterprise. I do not need that level of functionality, but as a Free user I do need to add non-geometric items to a BOM.

raj_Onshape

In OS you can create null assemblies and pre-create/evolve the entire assembly product structure ahead of time. It would be helpful if the same capability existed to create null parts devoid of geometry, or be comprised of simple sketches. I understand that OS multipart Part Studios complicates things, but it should be a simple thing to inherit/transfer properties (metadata) from a dummy part to the real part, or replace instances of a null part, or sketch, or surface in an assembly with the real part.

You can achieve this composite parts. One can insert composite parts into assembly and change the definition of composite parts within the part studio

StephenG

I fail to see how a "Composite Part" helps create a part devoid of geometry. A composite part must be composed of real 3D things, therefore, you have to have a surface, or volume in order to create a Composite Part.

Granted, a composite part, or a derived part, and even a surface (all which can be instanced into an assembly) does make it possible to formally associate/register important metadata (ex. part number) ahead of creating the part's real geometry. This would eliminate the need to have some sort of mechanism to transfer metadata to another part if the "null" part instance is replaced, but having an assembly containing instances of composite parts, or derived parts that are not true composite/derived parts would be confusing. I think it would be better to limit use of composite and derived part functionality to their original purpose.       

tim_hess427

I'm a little confused as to why you want sketches instanced in a BOM?  You mention that you want to have the part metadata show up in the BOM before the part geometry is defined. But why? 

I understand your frustration at not having access to "item" functionality - but I don't think assigning part metadata to a non-part is the way. If you're willing to go through the trouble of adding your metadata to a sketch, just take it one step further and extrude a sketch into a "placeholder" part and add that to your assembly. Then, just hide all of your placeholder parts in the assembly (you could use display states) so that they don't show up on the drawing, but metadata is still pulled into the drawing BOM. 

konstantin_shiriazdanov

I kinda can understand the use of part identity container, not only for assemblies but for situations when you for example inserting split or boolean operation, and all downstream features suddenly referencing the wrong piece. Or when you deciding to change the feature which creates initial part body, and loose forever all the references. This problem originates from the nature of part studios, where the part is so easy to create, and just as easy to loose its identity. So that you even have to intentionaly avoid of operations creating more then one part at time.

matthew_stacy

@StephenG, consider creating a "dummy part" that can be inserted into your assembly and then hidden.  That should show up in the BoM.  Would that suit your purpose?

Are you primarily interested in creating a placeholder for parts that have not been designed yet (as you previously stated)?  If so, think of the "dummy part" as THE part, that hasn't been detailed yet.  Unhide the part at some future date when you detail it.

Or are you trying to add BoM items that may never be modeled (such as adhesive)?

StephenG

@matthew_stacy, @konstantin_shiriazdanov

My rationale for wanting to add non-geometrical items to my assy BOM was to record the need for dispensable consumables critical to the assemblies function. I was modeling an outdoor wood product and during the design I wanted to record the use of a specific wood preservative and glue/adhesive. I know there are other ways to specify these things, but I didn't want to create a drawing and start propagating it with notes, or use OS comments which are easily overlooked. The assy BOM seemed like the logical choice to record this info. 
 
Due to the lack of access to BOM Item functionality, creating a "dummy part" was the approach I used. When I began, I asked myself what is the simplest thing (geometry wise) that would minimize visualization clutter and not mess with assy mass properties: a single point in a sketch was the obvious choice.  Turns out that a sketch was not a wise choice because you cannot assign metadata properties to it. So for this reason it doesn't make sense for instanced sketches to be included in the BOM. 

Ok, lets move up food chain, how about a curve created from a sketch line. Metadata properties can be added to curves, but wait you cannot insert/instance a curve into an assembly. Well, moving up the geometry food chain how about a simple planer 3-sided surface. This works, however, the mass property surface area calculation is wrong.

I ended up creating a OS Document full of small surfaces representing classes of non-geometrical BOM items. I instance the surface and then manually enter required info into the BOM entry fields. This is a imperfect workaround to address the lack of access to BOM Item functionality. 

It would be nice if Composite part could reference sketches, curves, and surfaces, or be created "null", but at least 1 part and only part data is supported.

Time to move on to developing the next work around.