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Very Simple Boolean Fails

janis_holmanjanis_holman Member Posts: 4
Hello,

I was working on a model that involved using booleans to create tab-and-slot joints for cnc machining. I wanted to offset certain faces to allow a clearance for fitment, but I didn't want to individually select a gazillion faces, so I was looking for a way to do an offset boolean and then use a linear pattern to create multiple instances of that geometry.



This approach worked well to generate the parts that I needed, but then I tried to boolean my whole model together to create a simplified "block" that I could use as a derived part in other part studios. This doesn't work.



The geometry is very simple, there is plenty of contact between the faces, no weird shapes ... but it doesn't work. Please let me know what you think. This is a url for the file:

https://cad.onshape.com/documents/e9201d60734dc348f6561414/w/54569915ca7f991d84e26090/e/22be82161c16fff7da9b4f95

Thanks you !

Answers

  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,310
    To be honest, I'm not 100% sure why that fails, but you don't need to boolean to derive.
    Senior Director, Technical Services, EMEAI
  • SethFSethF Member Posts: 129 PRO
    edited July 2022
    You've got corners coming together in an unsupported way. You either need these corners to overlap a little, or have a little gap. Onshape (and any CAD systems that use the same parasolid[?] kernel) can't work with that kind of geometry.

    I used to get frustrated with that behavior. But now it seems to make sense that this would be very hard to handle. At that point, that corner is kinda undefined. Is there an infinitely small gap? Or is there an infinitely small overlap? Are you making two interior, concave corners or two exterior, convex corners? Or maybe all four? But it's all one line. Feels a lot like wanting to be able to put 1/∞ as a dimension. Is an infinitely small volume super useful for developing accurate mathematical models with calculus? Yes definitely! Can you display one in a 3D model? Not easily/accurately..

    You can also think about it from a manufacturing stand point. If you were gonna mill that out of a block of aluminum, you'd either have a little bit of material left there, or you wouldn't! I guess, if you did some super fancy nanoscale manufacturing, you could get one string of atoms along that corner, but that's still overlapping my an atom  :D



  • janis_holmanjanis_holman Member Posts: 4
    @SethF Thank you for that explanation.


    I guess that is in fact happening at these highlighted locations. I thought it would be able to boolean everywhere else, but it makes sense to me now why that isn't possible.

    @NeilCooke I tried using a composite part instead of a boolean to simplify part studios before referencing them elsewhere and that is a much better approach. Thank you
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