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Large assembly modeling: what is the maximum reasonable size for an assembly

greg_appelgreg_appel Member Posts: 4
I am interested in knowing the assembly size limitations for Onshape.

Number of parts
Number of meg bytes
view-ability on screen

If anyone has a model of 5k or 10k parts, I would like to see it.

Thank you


  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 3,691
    Hi @greg_appel - are you evaluating Onshape for professional use? If so, please request a trial account and you can test your large assemblies for yourself. There is no limit on the number of parts or memory (on our servers at least, your browser may need more memory) , the usual limits depend on your graphics card which can be tested here: https://cad.onshape.com/check
    Director, Technical Services, EMEAI
  • lloyd_snelllloyd_snell Member Posts: 23 PRO
    I cannot show you my assembly, and Onshape is looking at the issue right now, but there seems to be a very hard limit. I must say, Onshape has progress significantly since my first try 3 years ago. I also would say there are many things that are very valuable. But, I may be experiencing the limitation of large assemblies. When that limit is reached, the component/assemblies imported no longer stay assembled during mating, and additionally are not constrained when place into the larger assembly. The modelling is no longer in control of mate relationship and parts are scattered all over the screen. At this point, I am unsure if there is a solution or a work around. This assembly is a very small one in my industry and represents only 1/50 of a very large assembly done in the past. So right now the failure occurs after approximately 5,019 parts, when the next 1673 parts are placed in the assembly the failure begins.  That would be close to 7,000 mates. Five days have been devoted to trying to get around the issue, with no luck. Onshape has access to this model and maybe, they could bring the detailed information from to better bound the limits I am experiencing. Maybe, there is a solution I don't know of yet. 
  • florianflorian Member, OS Professional Posts: 110 ✭✭✭
    @Józef_D that is a beautiful Assembly. What is the problem with it? It loads reasonably fast, uses 1.7 GB of ram and reloads even the smallest parts (Safety pins and that chain  <3 pretty well after zooming in.
  • alnis_smidchensalnis_smidchens Member Posts: 299 EDU
    edited August 2020
    I made a 3x3 pattern of a big project I worked on, here is a link (13,842 part instances total, 1,538 per subassembly): https://cad.onshape.com/documents/10ea50ebd6dccce088f0360d/w/b15e1c221028bed4bce5f10a/e/7e82e5bc434aba8473d58acd
    Admittedly, it is a lot of patterned parts (so the part count isn't truly representative of a big assembly memory-wise), but it is still an excellent example from a graphical test perspective for a complex project. It is usable (albeit slow) on my 7-year-old laptop with Intel HD 4000 integrated graphics, 8 GB DDR3-1600 MHz RAM, and 1.8 GHz dual-core i5-3337U. It's very smooth (25-30 FPS) on my brother's GTX 970 tower computer. Give it a spin (and make a copy if you'd like--then you can add fasteners and other things to see what assembly performance is like).

    (please ignore the past-EOL OS version B))
    Get in touch: [email protected] | My personal site: https://alnis.dev | My YouTube channel (I make tutorial videos for Onshape & Inventor): https://www.youtube.com/c/AlnisSmidchens
  • Józef_DJózef_D Member Posts: 10 ✭✭
    Thank you florian
    I have no problem with this model, I just wanted greg_appel to show a model consisting of over 5700 parts

  • john_mcclaryjohn_mcclary Member, Developers Posts: 3,191 PRO
    edited August 2020
    @greg_appel It really doesn't have as much to do with the qty of parts as it does the complexity of the shapes and the number of mates.

    pfftt get with the program Alnis!   ;)

  • alnis_smidchensalnis_smidchens Member Posts: 299 EDU
    @john_mcclary it's great to see another Pop!_OS user! I do have the latest version on my new laptop, I was just upstairs, and my old laptop was closer, so I used it to put together the pattern. It's amazing how lazy one can be with cloud-based CAD!
    Get in touch: [email protected] | My personal site: https://alnis.dev | My YouTube channel (I make tutorial videos for Onshape & Inventor): https://www.youtube.com/c/AlnisSmidchens
  • billy2billy2 Member, OS Professional, Mentor, Developers, User Group Leader Posts: 1,537 PRO
    How big can things get? I believe it's infinite. 

    -Be careful loading from step or parasolids into an assembly because these don't handle instancing properly which can kill an assembly. Please don't do what you did in an assembly. This isn't indicative of a real top level assembly.

    -I don't use a monster computer and run on a 12" macbook pro, not an impressive computer.

    The secret to infinite size is to manage your project and make things go away and come back. You don't have to work on the top level all the time. Break your design up into usable chunks, in my case, small chunks. On my little mac I rarely have more than 50 components on the screen at one time and I architect my projects to allow this.

    You can argue that when creating that wall poster image of the top level takes some time, I agree, it does. If your top assembly is this large, you should be creating simplified reps of the sub-assy's for displaying at the top level. Dropping details automatically has never been very good and I prefer building my simplified reps myself. You don't need a bolt inside a chassis in the top level assembly. You need strategies to make it go away and then come back. If your top level BOM is showing that bolt, you'll have problems.

    With the correct strategies I believe you could model the planet earth. It'd take a little ram, and you may get an email from Onshape asking "what the hell you doing?". I think it's possible, just not probable.

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