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Boolean Boss Battle
erik_goossens_saga
Member Posts: 9 ✭
I'm trying to add a boss to thickened circular surface. I want to turn this…
into this…
except what I really get is this: (see missing faces)
I'd be most grateful for any insights or suggestions.
I got there by Boolean-subracting a Negative tool…
and then Boolean-uniting a Positive tool…
0
Answers
If possible, it would be better to modify the outside shape as a solid and use the shell tool.
Have your main object. Then create plane and sketch for boss. Extrude boss to main object. Apply fillet to boss joint. Shell tool to hollow it out.
That… worked… thank you!
Though I'm perplexed, because the INITIAL thing that I tried (before the above approach) was to create the outer surface and then thicken it, but it errored out / didn't want to thicken.
And yet, take the same outer surface, build a flat-bottomed-plug onto it's bottom, and it shells just fine.
I thought thickening and shelling were fundamentally the same thing, in terms of the math being applied to a surface (so if one doesn't work then the other shouldn't either) - is that not so? What's the nuance to appreciate there?
Hi Erik,
In general, try and avoid the fillets being there already when thickening. when the thicken becomes self intersecting, it will create errors.
Shell CAN also run into these issues, but a little less likely.
I think your approach of adding/subtracting could also have worked if you'd have applied the fillet afterwards.
In building the positive and negative tools including the fillets to unite later, tolerance errors may creep into the fillets that will create problems in the unite/subract operation.downstream. Onshape is more robust handling these things than legacy CAD, but it's still not the best approach.
When you see references to self intersecting… this is one example of how that happens. Depending on your geometry OS will not know how to resolve things and calls it self intersecting. In this case its just the inside radius that's an issue. Making the radius bigger resolves it or if it were square cut it wouldn't be an issue. sometimes you might have to apply two radii after an operation like shell or thicken to get your desired result.
It wasn't a filleting issue - the curved surfaces of the boss was a loft.
Hi Erik,
yes i figured, for a regular fillet, onshape can sometimes figure out that it can leave a sharp corner and continue offsetting. for lofts, this is not possible.
It wasn't a fillet actually, it was a loft 🤔