I need to place a split down the back of my object how is that done?


BooleanSplit fails here.
The item is welded down the back face and so to do this I need to split it here, then ExtractSrf, select the appropriate surfaces and unrollSrf to get the 2D plan form of the item…
Rhino has joined my split up when I joined all surfaces and went MergeAllFaces as was suggested before filleting etc.
What method to split it here ?
how to split one part of a closed object.3dm (600.3 KB)


Steve, could you have 2 cutting surfaces a minimal separation apart? Then do what you need to do. —Mark

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Could you use intersect? When you unroll, you can bring the curves resulting from the intersection with you and then split.

Hi Markintheozarks,
I was wondering if one could in any circumstances split an object as such, especially if any micro gap was disallowed. On this occasion I could perhaps do that, though it could lead to error when grabbing a start point back there for a mirror etc.
(where are the ozarks by the way ? :slight_smile: )

Ryan, not sure if it wasnt split it would unroll . before using intersect. In my unroll accomplished by missing out a bend, the back panel has an isocurve down middle to trim with.

I did two then trimmed and joined them, but now see asymmetry (see other post)


‘Explode’ whole object
‘Split’ with cutter surface
‘Hide’ half the split surfaces
‘EdgesSrf’ the purple
‘join’ the half end plate still showing
‘unhide’ the other half
‘Hide’ the newly joined
Repeat steps above.
Unhide and join all with window selection

‘ExtractSrf’ the plate in grey temporarily for proof of success and rejoin

Rhino probably doesn’t let you split that part at only one location like that because the result will still be still one piece. You either need to have a physical gap (tiny, but there) or split it into two pieces.

There are a bunch of workarounds to end up where you want, the easiest might be to extract the 4 flat end surfaces to be split, join them to each other (not to the main body, just to themselves), BooleanSplit the joined surfaces with the plane, then join all three polysurface parts. You end up with a piece that has an internal split with 0 gap.

It is a high plateau in four states in the USA. Oklahoma, Missouri,Arkansas and Kansas.—- Mark

How about this:

Split face at seam location (red plane)
Move one half of the face with _SolidPtsOn (an arbitrary distance, keep in-plane).
Move the half face back using _SolidPtsOn.

This will give you an unjoined edge with no gap.

Use Booleandifference with a box so that it makes an actual gap and then use moveface to move the cut ends back to the position you want?

Hi Guys, Thanks,
all are good to know, the simplicity of robinp is interesting, having not used Moveface command before,. 4 steps to that… all are simple and a step more or so.



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Hello - if you Split the surfaces, than Join again, you can use UnjoinEdge to release, so to speak, the edges you want to be the seam on UnrollSrf.


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Hi Pascal,
thanks, just used that and worked a treat :slight_smile: