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Getting coincident sub-parts into one single part.

bruno_verachtenbruno_verachten Member Posts: 17
Hi there,

I regularly have an issue with Onshape, but I'm sure it's all my fault.
I draw a sketch with different shapes, and some of them are coincident (a circle touches a rectangle for example).
I then extrude the different shapes with various heights, with the hope that they will blend into one single part.
Unfortunately, it does not, with the error "The parts either do not intersect or are totally contained."
And of course, if I want to join them afterwards with the Union tool, I can't with the error "Boolean operation failed to return a valid part".
The latest illustration of my issue is there: https://cad.onshape.com/documents/de92b111aa7f5849203ae715/w/e26b7d6164ce3681e73079b7/e/5e7bbf0432d21953e263aed1

So... Does anyone know what I am doing wrong?

Thanks in advance,



  • Options
    NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,436
    edited July 2020
    It's all related to the "New Add Remove Intersect" options in the extrude dialog - if the objects touch during creation, Onshape will automatically set the option to Add - you can override this and select New to create a new part that you can boolean after.

    EDIT: or in your case, change the order of the features so that "Reinforcements" comes before "Pillars"
    Senior Director, Technical Services, EMEAI
  • Options
    Evan_ReeseEvan_Reese Member Posts: 2,068 PRO
    edited July 2020
    You also have "zero thickness geometry", which is why your boolean is failing. The pillars just exactly touch the side wall at a single edge, and Onshape (or any CAD software using the Parasolid kernel) can't combine those areas. If you make the circle for your pillar with a teeny-tiny gap or teeny-tiny overlap with the walls of the main body, it should combine no problem.

    Evan Reese / Principal and Industrial Designer with Ovyl
    Website: ovyl.io
  • Options
    bruno_verachtenbruno_verachten Member Posts: 17
    I see... Thanks, folks, I will experiment.
  • Options
    bruno_verachtenbruno_verachten Member Posts: 17
    I have understood why it failed and will proceed in a different way from now on.
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