Boolean Fail despite surfaces extruded to same line at same time

I hate Boolean Union !

I have rebuilt curves, created surfaces avoiding iso’s heading into one corner, bad practice for all nurbs.
they use a common line between them.
Used patch for the end ones.
join surfaces, then select the joined surface, run command solid extrude surface along line,
it asks me to select surfaces, yet they were selected, so select them one by one, choose red line,
get three solids, all made in exact same direction, their surfaces touching because the surfaces touched and were made to common lines, and joined at those edges, so it was happy then.

boolean union the resulting three separate solids on the black layer, fail…

BooleanUnionFail.3dm (220.9 KB)

why ?


Then don’t use it. Use the appropriate combination and sequence of Intersect, Trim, Split, ExtractSrf, Delete and Join.

Your example has coincident surfaces which frequently cause problems with the Boolean operations. Best to deal with then using the commands mentioned above.

Also, did you check the intersection between the objects? (BTW, I counted 4 objects that looked like should become one, not 3 - that makes it a bit harder for people that are trying to help to figure out what you are saying…).

The intersection between two of those should be a single closed polyline - instead there are 3 lines there. That is the reason why the boolean command fails in this example.

Just extract the concurrent surfaces with ExtractSrf and a window selection from the Front view, then Join… 5 second fix… --Mitch

Ignore the small item lower left.
I select the large solid with radiused edge, and the rectangular item, choose intersect, and see 4 lines ?
Its these two that fail, the centre item and smaller one with radiused edge booleaned ok.
Its why it failed , that puzzles me, I looked for intersect and with 4 lines resulting and knowing it was extruded along a straight line couldnt see that as the cause.
I wish Booleans were more tolerant of coincident surfaces, or had an option to move such together by the amount needed to succeed.

Hi Mitch so quickest fix ExtractSrf and join 5 secs.


For what it’s worth, boolean union works on this in V6. Boolean operations handle coincident surfaces much better there.

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Mitch, I run extractSrf then do a front view window selection then Join, yet the three objects still can be moved independently, yet it said joined.

Ah… I then do join again and now they are as one.

V6 comforting to know, life saver maybe.

When can we have V6 ?

If it fixes the layer bug I want it now :slight_smile:


You need to delete the extracted surfaces, then select the 3 objects then join.