Boolean union fail yet no naked edges


why wont these two parts A and B union ?
no naked edges,
Intersect well.

sides are same, I can create a cube then clone and abutt forming one longer 6 sides shape and it will union.

likewise A into C

also why not the screw thread, it intersects the cylinder and if i select each thread and do them one at a time they all union, but select them all and they wont union with the cylinder

Why wont D and E F G union into one item ? no naked edges.
BooleanDifference fail2.3dm (1.4 MB)

if anyone can fix these as job urgent and no time left to fiddle any more, unions do my head in.

I managed the thread one by one but is it ok and why did ot work that way if so ?

(Pascal Golay) #2

Hi Steve -

  1. when Boolean operations fail, the best way to diagnose the problem is to Intersect the objects and inspect the intersection curves if any.

  2. Boolean operations where surfaces and edges are coincident are likely to fail. Planar coincident surfaces will often work but non-planar ones never.

Remove all the coincident surfaces and the use Join, there is no reason to get involved with Boolean operations in your example.



Do you mean that you can do it without booleans?

Of course that’s OK. Using booleans for stuff like this just makes you do stupid things. They don’t help at all when doing work like this.
Mostly all you have to do is extract and delete all the extra surfaces that you never needed in the first place. You just went to a lot of work creating stuff you didn’t need because you thought it was the road to making booleans work when in fact it was the road to failure.
NoBoolean.3dm (1.0 MB)


Hi, thanks,
I had originally designed this in my earlier days in individual parts with never a need to union or combine it, then I get asked to do something in a hurry and union if it works is quick, and for almost all the parts, and these are just a few, it worked.

thank you fore the supplied 3dm as that got me out of a time pickle but just !

when I get 5 mins I will analyze and do it the correct way, only a day behind schedule now having had to use this in a way originally not designed, plus the hour trying to union it etc., fixed some in that time.