19 Replies Latest reply on Oct 30, 2014 9:31 AM by Brian McEwen

    Item numbers on Assembly Drawings

    Pete Yodis

      I am throwing this out there for discussion....  This is related to whether you show BOMs on Drawings and how you manage your BOMs with ERP and Drawings (and there could be implications with EPDM).  I am interested in hearing what other folks do...


      A little history on ourselves -  We moved away from showing the BOMs on assembly drawings about 7-8 years ago to reduce the amount of double entry for our designers managing a BOM table on drawings and a BOM in ERP.  I was not completely on board with the implementation, because SolidWorks implications were not being fully considered.  Most of the struggle atht he time was with editing tables in AutoCAD and then re-entering the data in ERP.  As a result, on all of our drawings we now just show the item number and do not show a BOM table.  The item number shown on the drawing has to match the Item number in ERP.  This gets "fun" for larger SolidWorks assembly drawings that go through multiple changes.  We have developed methods for keeping the Item numbers the same between ERP and SolidWorks assembly drawings.  As a trend, a single source of BOM is where companies are headed and keeping that master BOM in ERP seems like the best place for it to reside when you have CAD and ERP.  Frank B. Watts in his book, Engineering Documentation Control Handbook (2nd edition), agrees with an approach like this as a company grows and shows the trend in the future will be toward this method of a single BOM being mainatined in ERP (or PLM/PDM linked to ERP if you like).  I would agree with that approach, but it still makes item number management in SolidWorks drawings a pain. 


      This got me thinking about item numbers on drawings in general.  What is the point... It seems to be just a pointer to get you to some other controlled table so that you can find a unique identifier (part number)... hmmm seems to be jumping around a little bit and creating an extra step.  As part of the work order packet our production folks here print the BOM from ERP and print the drawing for assembly builds on the shop floor.  The assembly folks look at the drawing and find the ballooned item number, only to then look on the BOM and find that item number so they can get a part number.  The item numbers seem like the extra step... It seems to me that maybe item numbers are a carry over from a bygone era when drawings were hand drawn and BOMs were maintained on drawings.  Item numbers allowed easier changes to the BOM table without editing the drawing (when it was tedious to do by hand drawing).  Is there really a need for item numbers in a modern world?


      I am currently thinking out (with other's help here) why it wouldn't make sense just to show the part number of ballooned items on an assembly drawing and not the item number.  This would be much more efficient than having to consult another piece of information just to get what you are looking for.  Our assemblers would just see that unique identifier (part number) right on the drawing next to the item they are looking for.  I would advocate that the BOM in ERP be sorted to be in numberical order for easy reading and description location once the part number is seen on the drawing... or do show the BOM table on a SolidWorks drawing, but show it without item numbers and sorted by part number numerically.  This seems more efficient to me and would make looking at SolidWorks assembly drawing a nice thing.  Plus, we wouldn't have to go through the rigamarole of making item numbers match.


      Does anyone operate this way?  Can they see flaws with this approach?  Are item numbers really needed?  Let me know if I need to clarify.


      Thanks in Advance

        • Re: Item numbers on Assembly Drawings
          Brian Fairman

          my company creates and maintains the BOM using an ERP system. The assembly drawings have Find Number balloons which reference the BOM line item. We do NOT show part numbers or BOMs on the drawing itself.  This method provides a couple of advantages:

          1. We can revise the BOM without affecting the assembly drawing. Although editing the drawing is technically fairly easy nowadays, it's still and expensive process to ECO a drawing.

          2. We can designate alternate or substitute part numbers on the BOM for a single line item.


          Keeping Find Numbers on the assembly in sync with the BOM can be tedious for larger assemblies, but it's been my experience that it's really not that difficult if you manually populate the balloons rather than allowing Solidworks to automatically fill them in.  In fact, allowing Solidworks to populate the Find Number balloon has been an absolute disaster when a few inexperienced Engineers started to use that functionality, only to later realize the changes to the Assembly had completed screwed up thier drawing Find Numbers.  Expensive lesson learned.

            • Re: Item numbers on Assembly Drawings
              Pete Yodis



                Thank you your post and information on how your company runs.  With regards to SolidWorks on your points 1 and 2....


                   1)  Even if you don't revise the SolidWorks drawing to show a change in part number, wouldn't you still revise the assembly model behind the drawing?  My company moved to the method you describe when considering DWG files, but was not considering the dynamics involved with something like SolidWorks.  I think it is odd to not revise the drawing, and revise the model or not revise it.  It seems like its asking for trouble later.


                  2)  How would your assembly model capture alternate part numbers?  I wonder if SolidWorks needs to consider this methodology in order to properly capture this.  I have heard the ERP system we will eventaully move to (Epicore 9) has the ability for alternate part numbers in BOMs.


              I agree about the item numbers in balloons being tricky to manage.  We still have them as automatically assigned.  We follow the assembly order for the BOM on the drawing, use "not used" place holders to increment item numbers in the BOM, check to see the item numbers match between the drawing and ERP BOM, then hide the BOM table on the drawing.. leaving only the ballooned item numbers left.  Manually assigning the balloon number in SolidWorks seemed like too much work to me.  I think we also lost the ability to check the BOM to see if an item had been ballooned or not once this link was broken.

            • Re: Item numbers on Assembly Drawings
              Brian Fairman

              1) although it would be my preference to update the Solidworks assembly to reflect any BOM changes, the reality is that we do not. Understand that in our process, the Solidworks assembly does not drive anything downstream, it simply has to "look like" the final assembly on the drawing, so "close enough" is good enough.  Unfortunately that has lead to some lazy file management practices by our Engineers, which in turn leads to confusion in Enterprise PDM when the Composed Of list does not exactly match the ERP BOM. It has also caused problems on a few occasions when a contract requires that we deliver the source files (models and assemblies) to the customer and they don't jive with the delivered Parts Lists. Still, the perceived cost savings of not revising drawings/assemblies for every BOM change is seen as a more valuable than accurately maintaining the SW file structure.


              2) See answer to #1.  Essentially there is a disconnect between our drawings and our BOMs.


              Agreed, manually populating Find Number balloons can be a lot of work, but the auto-assign method comes with its own share of problems. Ultimately (IMO), the manual method is preferable

              • Re: Item numbers on Assembly Drawings
                Adrian Velazquez

                Pete, what industry are you in?


                Do you have a base product line?


                Do you Engineer to Order?


                Do your Engineers create the BOMs in the ERP, or does someone else down the line do it?

                  • Re: Item numbers on Assembly Drawings
                    Pete Yodis



                         We are industrial equipment. 


                    We do have a base product line, but we also do some customization for installations - usually how we mount up to customer's applications.  You could say portions of how we adapt to customer's applications are Engineered to Order. 


                    Our designers create the BOM in ERP.  With SolidWorks, we can export a BOM as a text file and then import that BOM the first time into ERP.  The editing of that BOM in ERP afterwards is a manual process.  We make sure the item numbers on the drawing match the item numbers in ERP.



                      • Re: Item numbers on Assembly Drawings
                        Adrian Velazquez

                        Interesting, we are 90% Engineered to order, so our methodology (and mine personally) is that the engineered drawings is what drives production (ERP should accommodate the drawing's BOM), so we would not foresee taking the BOMs out of the Engineered Drawings. Our engineers have limited access to our ERP system, but we are very enforcing on having drawing BOMs accurate, they later get imported to the ERP via test file.


                        This is an interesting discussion since we're in the verge of switching ERP Systems (most likely Dynamics AX) and it's the perfect time to review any process modifications/improvements.


                        How often do you experience issues where the ERP BOMs don't match what engineering intended?

                          • Re: Item numbers on Assembly Drawings
                            Pete Yodis



                                 We are also in the midst of switching ERP Systems (From Epicore Avante to Epicore 9).  It's been a long time in the making (4+ years now).  I have not been a part of that process at all, but have always been curious in the Microsoft ERP products (I secretly suspect those products are the better route for the long haul).  I do know that there is a struggle with the new ERP system here to let the designers here in the engineering department control the BOM and let manufacturing control other aspects of it.  The control seems like an all or nothing approach.  If both parties need access to change certain things in the BOM, then they both have full rights to everything (as I understand it).  I am involved in the migration from WorkGroup PDM (which I set up here 10 years ago) to EPDM.  I know that EPDM can handle BOMs and pass them off to ERP, but seems to be biting off more than we can chew at the moment.  I wonder if BOM control could be separated by having designers control the BOM in EPDM and it get passed to ERP where manufacturing then controls what they neeed.  But alas...thats a whole separate discussion.


                            We do not experience issues very often where the BOM is not as engineering intended because engineering controls the drawing item numbers and the BOM in ERP.  Our biggest struggle with BOMs and changes to them is the effectivity date of when those switchovers occur.  Often the new BOM is completed in ERP and not released for use because we are waiting for production to use up stock and tell us when to cut over for their planning needs.  This is probably more pertinent to a base product line... especially one's like ours that have been around and installed and supported and manfuactured for sometimes decades.  I'm not sure we have the best system here and maybe engineering and manufacturing's responsibilites aren't exactly figured right... but there's the history of how things are done that they are trying to match in the new system.


                            This is why I am questioning the use of item numbers on assembly drawings.  We are in the beginning of setting up EPDM, we are in midst of testing a new ERP system, and I am questioning why things are done a certain way.  Its good to see how others handle these issues and why they do what they do.  Sometimes as things change over the years, it no longer makes sense to keep doing them a certain way and we have to reflect on what it is we are actually doing.

                      • Re: Item numbers on Assembly Drawings
                        Glenn Schroeder

                        Hello Pete,


                        We don't use any form of outside document control here, so I can't address that part of your question, but I have just recently started moving away from using balloon numbers to call out parts.  I spent a lot of years reading drawings instead of creating them, and I got to thinking that I wouldn't want to continuously have to refer back to a BOM to see which part goes where, especially across multiple sheets.


                        I'm still including a BOM, but it's mostly just to indicate how many of each part is needed.  We don't use part numbers here either, just part names, so I have created a custom property that describes the part, and I use notes referencing this property that point to each part in the assembly drawing view, along with a column in the BOM.  Of course notes take up a little more room than balloons, but I'm making it work.  It's comparable to the PART NUMBER property from the standard BOM, but I prefer using the custom property instead because I can call it out in a note.  It's great that we can call out PART NUMBER in a balloon now, but I often want to add other information, so it works much better for me to have a note instead.


                        Anyway, maybe this doesn't address your post directly, but I did want to let you know that you're not the only one getting away from using balloons.

                          • Re: Item numbers on Assembly Drawings
                            John Burrill

                            This is a really important subject area and I believe it's one where the technology vendors are waiting for the User base to give them a direction.

                            I've tought about this issue a lot-having worked in environments with and without ERP systems and for managers that wanted BOMs on the drawings and ones that didn't.

                            Where I think you can parse this issue is in the answer to the question: What are your engineering drawings for?

                            You see, to the ERP-centric people-most of whom were in configuration management-the engineering drawing is a visual tool to assist manufacturing and purchasing.  They look on assembly drawings as a set of diagrams to supplement the ERP system, so they conclude the assembly drawing should be adapted to reflect the item master.  This logic convolutes the development process because it requires engineering to both supply the initial bom and then back their documents into compliance with implementation of the BOM in the ERP system prior to release.  There's no node in the change order flow chart to distinguish a design document from a production document, but in practice that distinction almost always exists.  This creates a decoupling of purchasing to engineering because now the purchasing management people can spec alternate part numbers to save on costs, insert find numbers for ancillary data like Test Procedures or fixtures and blindside the drawing out of compliance.  It's crazy because you'll have an ECO to release a product and then by the time it get's through purchasing to the shop floor, the drawing needs to be ECO'd to make the find numbers match the changes.

                            I finaly had an insight when my company shuffled around the managers and I got an engineering director who had been a manufacturing engineer at one point.  He basically told me, it isn't anybody's business outside of engineering what goes on an engineering drawing.  That sounds territorial at first but if you read into it, the only thing the final assembly drawing does is specify the product.  It exists for engineers to be able to explain the design to other engineers and the bill of materials on an engineering drawing really only serves to get the prototype built.  Once a product goes to manufacturing, it should have a completely different document that's in their specification control-like work instructions or routers and packing lists.  In this paradigm, the ERP/ECO system is naturally situated between engineering and manufacturing and changes can propogate from configuration management to manufacturing documentation.  This works out better than the idea that engineering should both lead and follow the business system.  And it allows engineering to use find numbers that make sense in the assembly model context without their having to shoe-horn in thinkgs like shrinkwrap, masking tape or solder flux. The purpose of a balloon is provide information about an assembly component, not to define the infrastructure for handling every contingency in every department in the organization. That would be like expecting a chef to write the receipt for your groceries into his recipe and then change the recipe if you go to a different store.
                            OK, so you don't automatically get find numbers in SolidWorks drawings that match the ERP find numbers, but is that really so important?  When you hear complaints about having to re-enter information, it's often prsented as if it's cheaper for an engineer to rework the design than it is for data-entry people to edit a list. I remember the config management administrator getting in a twist because the find numbers got shuffled on the drawing and he had to go through eight steps to correlate the ERP BOM to the drawing when really, all he should have had to do was read the ECO and not even look at the drawing.  It said replace partno X with partno Y, change the quantity on partno Z and add partno AA.  Was it really going to take longer for him to sort the table on the part number than it was for me to dissolve a circular pattern and remate all of the members so that the 3/8" screw could appear in the BOM above the 1/4" screws or add 4 dummy file instances with numberd configurations after every fastener to serve as placeholders for aletnerates to be specified by purchasing?  The fact is editing an assembly model carries a lot more overhead than an ERP system.

                            where the ERP system should drive the documentation is in the planning documents and routers because those originate in the ERP system.  You don't goto the assembly drawing to order SMC's for a PCB run.  When they make the assembly drawing, the engineer's not going to know whether to spec the capacitor in bulk, tape or reel quanities or switch to an alternate part number for a deviation or that cleaning optics takes 10 cotton balls and 1/2 an ounce of alchohol.  That's all information added outside of the engineer's control and while it is wise to track those consumables, it's not part of the product definition and doesn't belong in the engineering document.

                            I think what started this whole waste of energy over ERP driving the assembly drawing was the assumption that engineering = CAD and that using CAD data means controlling engineering and I think the answer is to give CAD data a life outside of engineering where it can leveraged and built upon by other departments without making design engineers into CAD butlers.

                            I'm strongly in favor of programs that allow CAD data to be transformed into the ERP item master and that make purchasing and other departmental information useable to engineering but this concept of a super-document built on the backs of designers proliferates ECO's and wastes engineering resources.

                            So I encourage people not to overburden that stupid little bubble.

                              • Re: Item numbers on Assembly Drawings
                                John Crist

                                John Burrill, am I right in concluding the following from your comments?


                                1.      If you write an ECO to replace partno X with partno Y, change the quantity on partno Z and add partno AA, you wouldn’t be required to make these changes in the CAD files?

                                2.      If manufacturing wants to change their assembling documents to have the 3/8" screw appear in the BOM above the 1/4" screws instead of below, you would not change the CAD files to show the change.

                                And, in the above scenarios, it would therefore be manufacturing’s responsibility/action to correctly update their documents using the ECO’s written description of change, as opposed to demanding updated CAD files from engineering, which they could basically use as-is.


                                  • Re: Item numbers on Assembly Drawings
                                    John Burrill

                                    That interpretation is correct with a couple of provisos.

                                    First this organization's manufacturing department used production redlines to get approval and track changes in manufacturing.  Basically, they would mark up the engineering document with the BOM changes or other modifications they wanted and get the program director to approve it.  The production redline would be incorporated into the engineering document as an ECO and I'd update the CAD data accordingly.  If on the other hand, they wanted to use use a different label for a specific customer, or use up inventory of a superseded component, those would be controlled with a deviation, and wouldn't have to be brought to my attention.

                                    Second, we tried to use general specifications for hardware and COTS items so as to give purchasing flexibility.  Additionally, purchasing and engineering created lists of approved alternates for some components that could be substituted without an ECO.

                                    Third-and this is really important-the engineering drawings were used by the manufacturing engineers to set up the lines, plan production and create their routers and work instructions.  Assemblers and techs didn't use engineering drawing to build production parts.  To that end, it was really important that the ERP system be able to cross-reference drawing information, but that it was otherwise self-contained. 

                                • Re: Item numbers on Assembly Drawings
                                  Pete Yodis

                                  Thanks Glenn,


                                     I have run into others as well...



                                    • Re: Item numbers on Assembly Drawings
                                      Pete Yodis

                                      Just to update ... We are now and have been for 6 months or so, creating assembly drawings without item numbers and listing the part numbers instead.  We are not showing the BOM table on the drawing, as that officially exists in ERP.  The shop floor sees the assembly drawing with the ballooned part numbers (five sided flag) along with the BOM printed from ERP and arranged in ascending part number order (no item numbers either).  The shop floor loves it and so do our designers controlling the documentation - no item number dances to keep them in sync.  So far its been a win-win.



                                        • Re: Item numbers on Assembly Drawings
                                          Brian McEwen

                                          Pete, Glad I ran across this, and it is cool you came back with an update. I had also questioned item number balloons as the ideal for some drawings.  When there is room on the paper I agree it seems like part numbers in balloons can be more clear and user friendly. In your earlier situation, syncing CAD and ERP item numbers sounded like a fragile and painful system.


                                          However, we won't be rushing to remove the BOM from our SolidWorks drawings.  It is not that hard to add (we just do Item, PN, Qty and Description) and it is a handy list.

                                          Even if the ERP BOM is the official BOM that you build to, having a CAD BOM to check your CAD model is helpful sometimes - it is good for documenting changes and checking that you are not missing a row. Until a change is implemented, I guess our drawing BOM is the official BOM for the next build.

                                          ... We also fill out a paper BOM change form when we do an EC, a bit redundant, it would be nice to automate that a bit more or partially link EPDM and our ERP.


                                          Our largest paper is 11x17.  So if usage for one bolt is split up over several pages, it is nice to have one location that gives the total.  By the way even with item numbers I usually sort the BOM by PN (and item numbers are simply sequential)  it is much easier to search through when you have more than 10 items.


                                          So anyway, I'd advocate using CAD BOMs when they are useful.


                                          Good luck with your impending EPDM launch. We are about 5 months in and it is getting better, migration fallout is still an occasional pain (data cards not populated, duplicates to fix, and stuff like that). Maybe you have already run files through your workflow - but if you still have the opportunity I recommend going more simple, reduce and add later. Overall I'd say EPDM has helped our productivity. It's been really nice for the new stuff created inside EPDM.