# Intersection of complex shapes failed

Hello.
Two object has one intersection - closed line (picture 1).
I wish to make a groove around intersection 3,5mm width and 1 mm deep.
All methods which I practiced from simple shapes (pict 2) to make a groove failed so far.
Issue is:

• two objects from picture 1 has one intersection
• created intersection has 14 intersection to outer shape
• and 7 intersections with plate
That is strange to me…
In order to get one intersection (non-segmented) with theses shapes I moved plate by -0,01mm but it didn’t worked out.
I can make a groove on plate alone by offsetting intersection (now two closed line do I have), create surface between them, extrude it and make a boolean difference with plate.
Point is, I can not later make a boolean union of such plate (with groove) to outer shape.

FORUM_SOLID_POLYSURFACES.3dm (3.0 MB)

Hi @Codi
Are you looking to cut the groove into the box and have them as one geometry? If yes: I’d start by extracting and deleting the back faces of the fuselage (or whatever it is) and use cap to generate a new, trimmed, single surface. Use dubborder to make a new outline and use offset to make a 3.5mm wider version. Extrude the dubborder and the offset 1mm and boolean difference from the box. You might need to manually close the offset, as the outline isn’t very clean. Or am I misunderstading the question?
HTH, Jakob
FORUM_SOLID_POLYSURFACES_JN.3dm (14.4 MB)

Dear Jakob.
FORUM_SOLID_POLYSURFACES_2.3dm (4.3 MB)
Thank you for feedback. I’ve tried as you advised and result is similar to previous tries.
I can make boolean union of fuselage and plate alone (no groove).
Result with groove is:

• fuseladge and plate can be merge with boolean union (no groove)
• groove can be “boolean differenced” with the plate
• fuselange can’t be “boolean unioned” with plate, if it has a groove
• groove can’t be placed if fuseladge and plate are already “bollean unioned”

I’ve tried your method, I have tried create base line for groove with intersection of the fuseladge and plate, I have tried duplicated edges on already unioned shape to get a groove and always “boolean difference failed”.

I belive there is a trick or a way how to do it, unfortunately I’m not aware of it

Hi @Codi
I can’t tell you why, but in the last file, the blue and green geomtries overlap a tiny bit - 0.01 mm or so. Zoom in really close on one of the corners to see (also see the attached pic). If you move either body or trim away the overlapping part off, it joins just fine.
HTH, Jakob

1 Like

Dear Jakob.
Yes you are right. There was 0.01mm displacement. I corrected it and repeated all steps, with no success…
On my PC “boolean union” fails
Finally I did work around - probably not perfect, but gave me result.
Duplicated border around shapes was firstly offseted by 0.001mm (like a small shell around fuselage).
From this “new” border finall offset 3.5mm was applied, later extrusion by 1mm and final “boolean difference”.
As final result, there is step 0.001mm around the fuseladge and it is below machine tolerance and it has no impact on mold milling, so … groove is done not elegant way but accepted
Still in a free time I will investigate why the groove can’t be done in a “typical” manner at least on my PC or in my mind set… (fuselage too complicated and needs “fiting surface” to some tolerance or…?)
Thank you very much for your concept and support - finally it works with a little 0.001 mod on my PC